From 4538fa22ab54b8d699a0e7ffa97dfc86cef95624 Mon Sep 17 00:00:00 2001
From: Kevin Barabash <kevinb@khanacademy.org>
Date: Thu, 16 Feb 2023 11:54:10 -0500
Subject: [PATCH] FEI-4957.4: Run codemod to convert files to TypeScript (#526)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

## Summary:
This changeset was generated using the follow commands:
- cd ../flow-to-typescript-codemod
- yarn typescriptify convert -p ../wonder-stuff --write --delete
- // manually change 'export {* as jest} from "jest"' to be 'export * as jest from "jest"' in wonder-stuff
- yarn typescriptify fix --autoSuppressErrors --jiraSlug FEI-5011 -p ../wonder-stuff --config ../wonder-stuff/tsconfig.json
- // manually rename prettierrc.ts to prettierrc.js
- cd ../wonder-stuff
- yarn format

The next PR will fix all the TypeScript errors

Issue: FEI-4957

## Test plan:
- yarn tsc --noEmit, see a bunch of errors

```
Found 24 errors in 7 files.

Errors  Files
     2  packages/wonder-stuff-i18n/src/utils/emoji-for-locale.ts:46
    10  packages/wonder-stuff-sentry/src/normalize-sentry-data.ts:34
     2  packages/wonder-stuff-server-google/src/start-server.ts:26
     1  packages/wonder-stuff-server/src/middleware/default-error-logging.ts:18
     1  packages/wonder-stuff-server/src/middleware/default-request-logging.ts:18
     4  packages/wonder-stuff-server/src/start-server.ts:37
     4  packages/wonder-stuff-server/src/types.ts:1
```

Author: kevinbarabash

Reviewers: jeresig, somewhatabstract, kevinbarabash

Required Reviewers:

Approved By: jeresig, somewhatabstract

Checks: ✅ CodeQL, ⏭  Test, ❌ Lint, flow, and coverage check (ubuntu-latest, 16.x), ✅ Analyze (javascript), ✅ gerald, ✅ Prime node_modules cache for primary configuration (ubuntu-latest, 16.x), ⏭  dependabot

Pull Request URL: https://github.com/Khan/wonder-stuff/pull/526
---
 .changeset/fifty-grapes-guess.md              |  11 +
 flow-typed/@google-cloud/logging-winston.js   |  37 ---
 flow-typed/express-winston.js                 |  51 ---
 flow-typed/superagent.js                      | 308 ------------------
 packages/eslint-config-khan/.prettierrc.js    |   1 -
 ...p => build-caused-by-message.test.ts.snap} |   0
 ...js.snap => errors-from-error.test.ts.snap} |   0
 ...r.test.js.snap => kind-error.test.ts.snap} |   0
 ...est.js => build-caused-by-message.test.ts} |   7 +-
 ...etadata.test.js => clone-metadata.test.ts} |  22 +-
 .../{clone.test.js => clone.test.ts}          |  11 +-
 ...ntries.flowtest.js => entries.flowtest.ts} |  18 +-
 .../{entries.test.js => entries.test.ts}      |   6 +-
 ...{error-info.test.js => error-info.test.ts} |  17 +-
 ...rror.test.js => errors-from-error.test.ts} |  11 +-
 .../{errors.test.js => errors.test.ts}        |   5 +-
 ...or.test.js => get-kind-from-error.test.ts} |   3 +-
 ... => get-original-stack-from-error.test.ts} |   1 -
 .../{keys.flowtest.js => keys.flowtest.ts}    |  13 +-
 .../__tests__/{keys.test.js => keys.test.ts}  |   7 +-
 ...{kind-error.test.js => kind-error.test.ts} |  22 +-
 ...ringify.test.js => safe-stringify.test.ts} |  25 +-
 ...middle.test.js => truncate-middle.test.ts} |   3 +-
 ...{values.flowtest.js => values.flowtest.ts} |  20 +-
 .../{values.test.js => values.test.ts}        |   7 +-
 ...-message.js => build-caused-by-message.ts} |   7 +-
 .../{clone-metadata.js => clone-metadata.ts}  |   8 +-
 .../src/{clone.js => clone.ts}                |   7 +-
 packages/wonder-stuff-core/src/entries.js     |  16 -
 .../src/{error-info.js => error-info.ts}      |  11 +-
 ...ors-from-error.js => errors-from-error.ts} |   6 +-
 .../src/{errors.js => errors.ts}              |   2 -
 ...d-from-error.js => get-kind-from-error.ts} |   1 -
 ...or.js => get-original-stack-from-error.ts} |   2 +-
 .../src/{index.js => index.ts}                |   4 +-
 packages/wonder-stuff-core/src/keys.js        |  13 -
 .../src/{kind-error.js => kind-error.ts}      |  46 +--
 .../{safe-stringify.js => safe-stringify.ts}  |  10 +-
 ...{truncate-middle.js => truncate-middle.ts} |   1 -
 .../src/{types.js => types.ts}                |   5 +-
 packages/wonder-stuff-core/src/values.js      |  14 -
 ...ll-i18n-strings.js => all-i18n-strings.ts} |   1 -
 .../bin/{gen-potfile.js => gen-potfile.ts}    |   1 -
 .../src/{index.js => index.ts}                |   1 -
 ...18n-plugin.test.js => i18n-plugin.test.ts} |  70 ++--
 .../{i18n-plugin.js => i18n-plugin.ts}        |  95 +++---
 ...ocale.test.js => emoji-for-locale.test.ts} |   1 -
 ...ract-i18n.test.js => extract-i18n.test.ts} |   5 +-
 ...{i18n-utils.test.js => i18n-utils.test.ts} |   9 +-
 ...ize-file.test.js => localize-file.test.ts} |  29 +-
 ...ile-utils.test.js => pofile-utils.test.ts} |  38 ++-
 ...moji-for-locale.js => emoji-for-locale.ts} |   4 +-
 .../{extract-i18n.js => extract-i18n.ts}      |  25 +-
 .../utils/{i18n-utils.js => i18n-utils.ts}    |  15 +-
 .../{localize-file.js => localize-file.ts}    |  26 +-
 .../{pofile-utils.js => pofile-utils.ts}      |  19 +-
 ...t.js.snap => kind-error-data.test.ts.snap} |   0
 ...ta.test.js => collate-sentry-data.test.ts} |  13 +-
 ....js => get-sentry-data-from-error.test.ts} |   6 +-
 ...s => is-reserved-context-property.test.ts} |   3 +-
 ...ey.test.js => is-reserved-tag-key.test.ts} |   3 +-
 ...valid.test.js => is-tag-key-valid.test.ts} |   7 +-
 ...r-data.test.js => kind-error-data.test.ts} |  70 ++--
 ...rror.test.js => kind-sentry-error.test.ts} |   8 +-
 ....test.js => normalize-sentry-data.test.ts} |  28 +-
 ...er.test.js => sentry-data-reducer.test.ts} |   5 +-
 ...lue.test.js => truncate-tag-value.test.ts} |   3 +-
 ...-sentry-data.js => collate-sentry-data.ts} |  11 +-
 ....js => default-kind-error-data-options.ts} |   1 -
 ...ty-sentry-data.js => empty-sentry-data.ts} |   3 +-
 ...error.js => get-sentry-data-from-error.ts} |   3 +-
 .../src/{index.js => index.ts}                |   1 -
 ...rty.js => is-reserved-context-property.ts} |   1 -
 ...rved-tag-key.js => is-reserved-tag-key.ts} |   1 -
 ...s-tag-key-valid.js => is-tag-key-valid.ts} |   2 -
 ...{kind-error-data.js => kind-error-data.ts} |  18 +-
 ...d-sentry-error.js => kind-sentry-error.ts} |  30 +-
 ...entry-data.js => normalize-sentry-data.ts} |  23 +-
 ...data-reducer.js => sentry-data-reducer.ts} |   8 +-
 ...ate-tag-value.js => truncate-tag-value.ts} |   1 -
 .../src/{types.js => types.ts}                |  67 ++--
 ...l.test.js.snap => trace-impl.test.ts.snap} |   0
 ...t.js => add-app-engine-middleware.test.ts} |  65 ++--
 ...fo.test.js => get-app-engine-info.test.ts} |   3 +-
 ...st.js => get-appengine-request-id.test.ts} |  17 +-
 .../{get-delta.test.js => get-delta.test.ts}  |   6 +-
 ...ons.test.js => setup-integrations.test.ts} |  40 +--
 ...rt-server.test.js => start-server.test.ts} |  35 +-
 ...{trace-impl.test.js => trace-impl.test.ts} |  89 +++--
 .../{trace.test.js => trace.test.ts}          |  47 ++-
 ...leware.js => add-app-engine-middleware.ts} |  17 +-
 ...-engine-info.js => get-app-engine-info.ts} |   1 -
 ...est-id.js => get-app-engine-request-id.ts} |   7 +-
 ...etadata.js => get-default-log-metadata.ts} |   5 +-
 .../src/get-delta.js                          |  13 -
 .../src/get-delta.ts                          |  13 +
 .../src/{index.js => index.ts}                |   1 -
 ...-app-engine-request-id-middleware.test.ts} |  78 ++---
 ... make-app-engine-request-id-middleware.ts} |  10 +-
 ...-integrations.js => setup-integrations.ts} |   3 +-
 .../src/{start-server.js => start-server.ts}  |  12 +-
 .../src/{trace-impl.js => trace-impl.ts}      |  14 +-
 .../src/{trace.js => trace.ts}                |  11 +-
 .../src/{types.js => types.ts}                |  49 +--
 ...nap => get-logging-transport.test.ts.snap} |   0
 ...e-logger.test.js => create-logger.test.ts} |  24 +-
 ...-url.test.js => get-agent-for-url.test.ts} |   1 -
 ...{get-logger.test.js => get-logger.test.ts} |  16 +-
 ....test.js => get-logging-transport.test.ts} |  13 +-
 ...ger.test.js => get-request-logger.test.ts} |  17 +-
 ...-mode.test.js => get-runtime-mode.test.ts} |  24 +-
 ...oot-logger.test.js => root-logger.test.ts} |   7 +-
 ...rt-server.test.js => start-server.test.ts} | 296 ++++++++---------
 .../{create-logger.js => create-logger.ts}    |   6 +-
 .../src/{errors.js => errors.ts}              |   1 -
 ...-agent-for-url.js => get-agent-for-url.ts} |   3 +-
 .../src/{get-logger.js => get-logger.ts}      |   5 +-
 ...-transport.js => get-logging-transport.ts} |   9 +-
 ...equest-logger.js => get-request-logger.ts} |   7 +-
 ...et-runtime-mode.js => get-runtime-mode.ts} |   5 +-
 .../src/{index.js => index.ts}                |   1 -
 ....test.js => default-error-logging.test.ts} |   9 +-
 ...est.js => default-request-logging.test.ts} |   9 +-
 .../src/middleware/default-error-logging.js   |  19 --
 .../src/middleware/default-error-logging.ts   |  22 ++
 ...-logging.js => default-request-logging.ts} |  17 +-
 .../src/middleware/{index.js => index.ts}     |   1 -
 .../src/{root-logger.js => root-logger.ts}    |   5 +-
 .../src/{start-server.js => start-server.ts}  |  33 +-
 .../src/{types.js => types.ts}                |  56 ++--
 ...y-for.test.js => data-factory-for.test.ts} |  12 +-
 ...ata-factory-for.js => data-factory-for.ts} |   6 +-
 .../src/{index.js => index.ts}                |   1 -
 ...odules.test.js => isolate-modules.test.ts} |   1 -
 .../__tests__/{wait.test.js => wait.test.ts}  |   1 -
 .../src/jest/{index.js => index.ts}           |   1 -
 ...ssert-jest.test.js => assert-jest.test.ts} |   1 -
 ...d-wait.test.js => unverified-wait.test.ts} |  12 +-
 ...ers.test.js => verify-real-timers.test.ts} |   1 -
 .../{assert-jest.js => assert-jest.ts}        |   1 -
 ...nning-in-jest.js => is-running-in-jest.ts} |   1 -
 .../src/jest/internal/unverified-wait.js      |  12 -
 .../src/jest/internal/unverified-wait.ts      |  18 +
 ...y-real-timers.js => verify-real-timers.ts} |   3 -
 ...{isolate-modules.js => isolate-modules.ts} |   3 +-
 .../src/jest/{wait.js => wait.ts}             |  10 +-
 146 files changed, 1095 insertions(+), 1545 deletions(-)
 create mode 100644 .changeset/fifty-grapes-guess.md
 delete mode 100644 flow-typed/@google-cloud/logging-winston.js
 delete mode 100644 flow-typed/express-winston.js
 delete mode 100644 flow-typed/superagent.js
 rename packages/wonder-stuff-core/src/__tests__/__snapshots__/{build-caused-by-message.test.js.snap => build-caused-by-message.test.ts.snap} (100%)
 rename packages/wonder-stuff-core/src/__tests__/__snapshots__/{errors-from-error.test.js.snap => errors-from-error.test.ts.snap} (100%)
 rename packages/wonder-stuff-core/src/__tests__/__snapshots__/{kind-error.test.js.snap => kind-error.test.ts.snap} (100%)
 rename packages/wonder-stuff-core/src/__tests__/{build-caused-by-message.test.js => build-caused-by-message.test.ts} (95%)
 rename packages/wonder-stuff-core/src/__tests__/{clone-metadata.test.js => clone-metadata.test.ts} (67%)
 rename packages/wonder-stuff-core/src/__tests__/{clone.test.js => clone.test.ts} (95%)
 rename packages/wonder-stuff-core/src/__tests__/{entries.flowtest.js => entries.flowtest.ts} (70%)
 rename packages/wonder-stuff-core/src/__tests__/{entries.test.js => entries.test.ts} (85%)
 rename packages/wonder-stuff-core/src/__tests__/{error-info.test.js => error-info.test.ts} (92%)
 rename packages/wonder-stuff-core/src/__tests__/{errors-from-error.test.js => errors-from-error.test.ts} (83%)
 rename packages/wonder-stuff-core/src/__tests__/{errors.test.js => errors.test.ts} (61%)
 rename packages/wonder-stuff-core/src/__tests__/{get-kind-from-error.test.js => get-kind-from-error.test.ts} (96%)
 rename packages/wonder-stuff-core/src/__tests__/{get-original-stack-from-error.test.js => get-original-stack-from-error.test.ts} (99%)
 rename packages/wonder-stuff-core/src/__tests__/{keys.flowtest.js => keys.flowtest.ts} (71%)
 rename packages/wonder-stuff-core/src/__tests__/{keys.test.js => keys.test.ts} (72%)
 rename packages/wonder-stuff-core/src/__tests__/{kind-error.test.js => kind-error.test.ts} (94%)
 rename packages/wonder-stuff-core/src/__tests__/{safe-stringify.test.js => safe-stringify.test.ts} (87%)
 rename packages/wonder-stuff-core/src/__tests__/{truncate-middle.test.js => truncate-middle.test.ts} (96%)
 rename packages/wonder-stuff-core/src/__tests__/{values.flowtest.js => values.flowtest.ts} (73%)
 rename packages/wonder-stuff-core/src/__tests__/{values.test.js => values.test.ts} (73%)
 rename packages/wonder-stuff-core/src/{build-caused-by-message.js => build-caused-by-message.ts} (83%)
 rename packages/wonder-stuff-core/src/{clone-metadata.js => clone-metadata.ts} (78%)
 rename packages/wonder-stuff-core/src/{clone.js => clone.ts} (69%)
 delete mode 100644 packages/wonder-stuff-core/src/entries.js
 rename packages/wonder-stuff-core/src/{error-info.js => error-info.ts} (97%)
 rename packages/wonder-stuff-core/src/{errors-from-error.js => errors-from-error.ts} (82%)
 rename packages/wonder-stuff-core/src/{errors.js => errors.ts} (98%)
 rename packages/wonder-stuff-core/src/{get-kind-from-error.js => get-kind-from-error.ts} (96%)
 rename packages/wonder-stuff-core/src/{get-original-stack-from-error.js => get-original-stack-from-error.ts} (72%)
 rename packages/wonder-stuff-core/src/{index.js => index.ts} (61%)
 delete mode 100644 packages/wonder-stuff-core/src/keys.js
 rename packages/wonder-stuff-core/src/{kind-error.js => kind-error.ts} (88%)
 rename packages/wonder-stuff-core/src/{safe-stringify.js => safe-stringify.ts} (96%)
 rename packages/wonder-stuff-core/src/{truncate-middle.js => truncate-middle.ts} (99%)
 rename packages/wonder-stuff-core/src/{types.js => types.ts} (58%)
 delete mode 100644 packages/wonder-stuff-core/src/values.js
 rename packages/wonder-stuff-i18n/src/bin/{all-i18n-strings.js => all-i18n-strings.ts} (98%)
 mode change 100755 => 100644
 rename packages/wonder-stuff-i18n/src/bin/{gen-potfile.js => gen-potfile.ts} (99%)
 mode change 100755 => 100644
 rename packages/wonder-stuff-i18n/src/{index.js => index.ts} (98%)
 rename packages/wonder-stuff-i18n/src/plugins/__tests__/{i18n-plugin.test.js => i18n-plugin.test.ts} (90%)
 rename packages/wonder-stuff-i18n/src/plugins/{i18n-plugin.js => i18n-plugin.ts} (88%)
 rename packages/wonder-stuff-i18n/src/utils/__tests__/{emoji-for-locale.test.js => emoji-for-locale.test.ts} (98%)
 rename packages/wonder-stuff-i18n/src/utils/__tests__/{extract-i18n.test.js => extract-i18n.test.ts} (99%)
 rename packages/wonder-stuff-i18n/src/utils/__tests__/{i18n-utils.test.js => i18n-utils.test.ts} (97%)
 rename packages/wonder-stuff-i18n/src/utils/__tests__/{localize-file.test.js => localize-file.test.ts} (94%)
 rename packages/wonder-stuff-i18n/src/utils/__tests__/{pofile-utils.test.js => pofile-utils.test.ts} (76%)
 rename packages/wonder-stuff-i18n/src/utils/{emoji-for-locale.js => emoji-for-locale.ts} (79%)
 rename packages/wonder-stuff-i18n/src/utils/{extract-i18n.js => extract-i18n.ts} (96%)
 rename packages/wonder-stuff-i18n/src/utils/{i18n-utils.js => i18n-utils.ts} (88%)
 rename packages/wonder-stuff-i18n/src/utils/{localize-file.js => localize-file.ts} (92%)
 rename packages/wonder-stuff-i18n/src/utils/{pofile-utils.js => pofile-utils.ts} (92%)
 rename packages/wonder-stuff-sentry/src/__tests__/__snapshots__/{kind-error-data.test.js.snap => kind-error-data.test.ts.snap} (100%)
 rename packages/wonder-stuff-sentry/src/__tests__/{collate-sentry-data.test.js => collate-sentry-data.test.ts} (97%)
 rename packages/wonder-stuff-sentry/src/__tests__/{get-sentry-data-from-error.test.js => get-sentry-data-from-error.test.ts} (75%)
 rename packages/wonder-stuff-sentry/src/__tests__/{is-reserved-context-property.test.js => is-reserved-context-property.test.ts} (68%)
 rename packages/wonder-stuff-sentry/src/__tests__/{is-reserved-tag-key.test.js => is-reserved-tag-key.test.ts} (73%)
 rename packages/wonder-stuff-sentry/src/__tests__/{is-tag-key-valid.test.js => is-tag-key-valid.test.ts} (66%)
 rename packages/wonder-stuff-sentry/src/__tests__/{kind-error-data.test.js => kind-error-data.test.ts} (84%)
 rename packages/wonder-stuff-sentry/src/__tests__/{kind-sentry-error.test.js => kind-sentry-error.test.ts} (92%)
 rename packages/wonder-stuff-sentry/src/__tests__/{normalize-sentry-data.test.js => normalize-sentry-data.test.ts} (90%)
 rename packages/wonder-stuff-sentry/src/__tests__/{sentry-data-reducer.test.js => sentry-data-reducer.test.ts} (99%)
 rename packages/wonder-stuff-sentry/src/__tests__/{truncate-tag-value.test.js => truncate-tag-value.test.ts} (95%)
 rename packages/wonder-stuff-sentry/src/{collate-sentry-data.js => collate-sentry-data.ts} (90%)
 rename packages/wonder-stuff-sentry/src/{default-kind-error-data-options.js => default-kind-error-data-options.ts} (97%)
 rename packages/wonder-stuff-sentry/src/{empty-sentry-data.js => empty-sentry-data.ts} (63%)
 rename packages/wonder-stuff-sentry/src/{get-sentry-data-from-error.js => get-sentry-data-from-error.ts} (91%)
 rename packages/wonder-stuff-sentry/src/{index.js => index.ts} (96%)
 rename packages/wonder-stuff-sentry/src/{is-reserved-context-property.js => is-reserved-context-property.ts} (98%)
 rename packages/wonder-stuff-sentry/src/{is-reserved-tag-key.js => is-reserved-tag-key.ts} (98%)
 rename packages/wonder-stuff-sentry/src/{is-tag-key-valid.js => is-tag-key-valid.ts} (98%)
 rename packages/wonder-stuff-sentry/src/{kind-error-data.js => kind-error-data.ts} (90%)
 rename packages/wonder-stuff-sentry/src/{kind-sentry-error.js => kind-sentry-error.ts} (90%)
 rename packages/wonder-stuff-sentry/src/{normalize-sentry-data.js => normalize-sentry-data.ts} (89%)
 rename packages/wonder-stuff-sentry/src/{sentry-data-reducer.js => sentry-data-reducer.ts} (91%)
 rename packages/wonder-stuff-sentry/src/{truncate-tag-value.js => truncate-tag-value.ts} (98%)
 rename packages/wonder-stuff-sentry/src/{types.js => types.ts} (76%)
 rename packages/wonder-stuff-server-google/src/__tests__/__snapshots__/{trace-impl.test.js.snap => trace-impl.test.ts.snap} (100%)
 rename packages/wonder-stuff-server-google/src/__tests__/{add-app-engine-middleware.test.js => add-app-engine-middleware.test.ts} (74%)
 rename packages/wonder-stuff-server-google/src/__tests__/{get-app-engine-info.test.js => get-app-engine-info.test.ts} (96%)
 rename packages/wonder-stuff-server-google/src/__tests__/{get-appengine-request-id.test.js => get-appengine-request-id.test.ts} (83%)
 rename packages/wonder-stuff-server-google/src/__tests__/{get-delta.test.js => get-delta.test.ts} (66%)
 rename packages/wonder-stuff-server-google/src/__tests__/{setup-integrations.test.js => setup-integrations.test.ts} (72%)
 rename packages/wonder-stuff-server-google/src/__tests__/{start-server.test.js => start-server.test.ts} (86%)
 rename packages/wonder-stuff-server-google/src/__tests__/{trace-impl.test.js => trace-impl.test.ts} (73%)
 rename packages/wonder-stuff-server-google/src/__tests__/{trace.test.js => trace.test.ts} (76%)
 rename packages/wonder-stuff-server-google/src/{add-app-engine-middleware.js => add-app-engine-middleware.ts} (63%)
 rename packages/wonder-stuff-server-google/src/{get-app-engine-info.js => get-app-engine-info.ts} (98%)
 rename packages/wonder-stuff-server-google/src/{get-app-engine-request-id.js => get-app-engine-request-id.ts} (87%)
 rename packages/wonder-stuff-server-google/src/{get-default-log-metadata.js => get-default-log-metadata.ts} (79%)
 delete mode 100644 packages/wonder-stuff-server-google/src/get-delta.js
 create mode 100644 packages/wonder-stuff-server-google/src/get-delta.ts
 rename packages/wonder-stuff-server-google/src/{index.js => index.ts} (92%)
 rename packages/wonder-stuff-server-google/src/middleware/__tests__/{make-app-engine-request-id-middleware.test.js => make-app-engine-request-id-middleware.test.ts} (65%)
 rename packages/wonder-stuff-server-google/src/middleware/{make-app-engine-request-id-middleware.js => make-app-engine-request-id-middleware.ts} (80%)
 rename packages/wonder-stuff-server-google/src/{setup-integrations.js => setup-integrations.ts} (94%)
 rename packages/wonder-stuff-server-google/src/{start-server.js => start-server.ts} (86%)
 rename packages/wonder-stuff-server-google/src/{trace-impl.js => trace-impl.ts} (92%)
 rename packages/wonder-stuff-server-google/src/{trace.js => trace.ts} (89%)
 rename packages/wonder-stuff-server-google/src/{types.js => types.ts} (83%)
 rename packages/wonder-stuff-server/src/__tests__/__snapshots__/{get-logging-transport.test.js.snap => get-logging-transport.test.ts.snap} (100%)
 rename packages/wonder-stuff-server/src/__tests__/{create-logger.test.js => create-logger.test.ts} (72%)
 rename packages/wonder-stuff-server/src/__tests__/{get-agent-for-url.test.js => get-agent-for-url.test.ts} (99%)
 rename packages/wonder-stuff-server/src/__tests__/{get-logger.test.js => get-logger.test.ts} (67%)
 rename packages/wonder-stuff-server/src/__tests__/{get-logging-transport.test.js => get-logging-transport.test.ts} (74%)
 rename packages/wonder-stuff-server/src/__tests__/{get-request-logger.test.js => get-request-logger.test.ts} (77%)
 rename packages/wonder-stuff-server/src/__tests__/{get-runtime-mode.test.js => get-runtime-mode.test.ts} (76%)
 rename packages/wonder-stuff-server/src/__tests__/{root-logger.test.js => root-logger.test.ts} (84%)
 rename packages/wonder-stuff-server/src/__tests__/{start-server.test.js => start-server.test.ts} (87%)
 rename packages/wonder-stuff-server/src/{create-logger.js => create-logger.ts} (69%)
 rename packages/wonder-stuff-server/src/{errors.js => errors.ts} (99%)
 rename packages/wonder-stuff-server/src/{get-agent-for-url.js => get-agent-for-url.ts} (97%)
 rename packages/wonder-stuff-server/src/{get-logger.js => get-logger.ts} (88%)
 rename packages/wonder-stuff-server/src/{get-logging-transport.js => get-logging-transport.ts} (89%)
 rename packages/wonder-stuff-server/src/{get-request-logger.js => get-request-logger.ts} (82%)
 rename packages/wonder-stuff-server/src/{get-runtime-mode.js => get-runtime-mode.ts} (89%)
 rename packages/wonder-stuff-server/src/{index.js => index.ts} (98%)
 rename packages/wonder-stuff-server/src/middleware/__tests__/{default-error-logging.test.js => default-error-logging.test.ts} (81%)
 rename packages/wonder-stuff-server/src/middleware/__tests__/{default-request-logging.test.js => default-request-logging.test.ts} (81%)
 delete mode 100644 packages/wonder-stuff-server/src/middleware/default-error-logging.js
 create mode 100644 packages/wonder-stuff-server/src/middleware/default-error-logging.ts
 rename packages/wonder-stuff-server/src/middleware/{default-request-logging.js => default-request-logging.ts} (64%)
 rename packages/wonder-stuff-server/src/middleware/{index.js => index.ts} (93%)
 rename packages/wonder-stuff-server/src/{root-logger.js => root-logger.ts} (78%)
 rename packages/wonder-stuff-server/src/{start-server.js => start-server.ts} (90%)
 rename packages/wonder-stuff-server/src/{types.js => types.ts} (68%)
 rename packages/wonder-stuff-testing/src/__tests__/{data-factory-for.test.js => data-factory-for.test.ts} (65%)
 rename packages/wonder-stuff-testing/src/{data-factory-for.js => data-factory-for.ts} (89%)
 rename packages/wonder-stuff-testing/src/{index.js => index.ts} (90%)
 rename packages/wonder-stuff-testing/src/jest/__tests__/{isolate-modules.test.js => isolate-modules.test.ts} (99%)
 rename packages/wonder-stuff-testing/src/jest/__tests__/{wait.test.js => wait.test.ts} (99%)
 rename packages/wonder-stuff-testing/src/jest/{index.js => index.ts} (89%)
 rename packages/wonder-stuff-testing/src/jest/internal/__tests__/{assert-jest.test.js => assert-jest.test.ts} (98%)
 rename packages/wonder-stuff-testing/src/jest/internal/__tests__/{unverified-wait.test.js => unverified-wait.test.ts} (72%)
 rename packages/wonder-stuff-testing/src/jest/internal/__tests__/{verify-real-timers.test.js => verify-real-timers.test.ts} (99%)
 rename packages/wonder-stuff-testing/src/jest/internal/{assert-jest.js => assert-jest.ts} (97%)
 rename packages/wonder-stuff-testing/src/jest/internal/{is-running-in-jest.js => is-running-in-jest.ts} (97%)
 delete mode 100644 packages/wonder-stuff-testing/src/jest/internal/unverified-wait.js
 create mode 100644 packages/wonder-stuff-testing/src/jest/internal/unverified-wait.ts
 rename packages/wonder-stuff-testing/src/jest/internal/{verify-real-timers.js => verify-real-timers.ts} (94%)
 rename packages/wonder-stuff-testing/src/jest/{isolate-modules.js => isolate-modules.ts} (90%)
 rename packages/wonder-stuff-testing/src/jest/{wait.js => wait.ts} (93%)

diff --git a/.changeset/fifty-grapes-guess.md b/.changeset/fifty-grapes-guess.md
new file mode 100644
index 00000000..2256e8ed
--- /dev/null
+++ b/.changeset/fifty-grapes-guess.md
@@ -0,0 +1,11 @@
+---
+"@khanacademy/wonder-stuff-server-google": minor
+"@khanacademy/wonder-stuff-testing": minor
+"@khanacademy/wonder-stuff-sentry": minor
+"@khanacademy/wonder-stuff-server": minor
+"@khanacademy/eslint-config": minor
+"@khanacademy/wonder-stuff-core": minor
+"@khanacademy/wonder-stuff-i18n": minor
+---
+
+Migrate to TypeScript
diff --git a/flow-typed/@google-cloud/logging-winston.js b/flow-typed/@google-cloud/logging-winston.js
deleted file mode 100644
index a3729c76..00000000
--- a/flow-typed/@google-cloud/logging-winston.js
+++ /dev/null
@@ -1,37 +0,0 @@
-// @flow
-declare module "@google-cloud/logging-winston" {
-    declare type loggingwinston$Callback = (
-        err: Error,
-        apiResponse: {...},
-    ) => void;
-
-    declare interface loggingwinston$Options {
-        // TODO: Fill this out
-    }
-    declare class loggingwinston$LoggingWinston extends $winstonTransport {
-        constructor(options?: loggingwinston$Options): this;
-        log(info: any, callback: loggingwinston$Callback): void;
-    }
-
-    declare interface loggingwinston$express {
-        makeMiddleware<
-            Req: express$Request = express$Request,
-            Res: express$Response = express$Response,
-        >(
-            logger: $winstonLogger<$winstonNpmLogLevels>,
-            transport: loggingwinston$LoggingWinston,
-        ): Promise<express$Middleware<Req, Res>>;
-        makeMiddleware<
-            Req: express$Request = express$Request,
-            Res: express$Response = express$Response,
-        >(
-            logger: $winstonLogger<$winstonNpmLogLevels>,
-            options?: loggingwinston$Options,
-        ): Promise<express$Middleware<Req, Res>>;
-    }
-
-    declare module.exports: {
-        LoggingWinston: typeof loggingwinston$LoggingWinston,
-        express: loggingwinston$express,
-    };
-}
diff --git a/flow-typed/express-winston.js b/flow-typed/express-winston.js
deleted file mode 100644
index 782e06e6..00000000
--- a/flow-typed/express-winston.js
+++ /dev/null
@@ -1,51 +0,0 @@
-// @flow
-declare module "express-winston" {
-    declare type express$Handler = (
-        req: express$Request,
-        res: express$Response,
-        next: express$NextFunction,
-    ) => mixed;
-    declare type express$ErrorRequestHandler = (
-        error: Error,
-        req: express$Request,
-        res: express$Response,
-        next: express$NextFunction,
-    ) => mixed;
-
-    declare interface expresswinston$BaseLoggerOptions {
-        expressFormat?: boolean;
-        format?: $winstonFormat;
-        level?: string;
-        meta?: boolean;
-    }
-
-    declare type expresswinston$LoggerOptionsWithTransports = {
-        transports?: Array<$winstonTransport>,
-        ...
-    } & expresswinston$BaseLoggerOptions;
-
-    declare type expresswinston$LoggerOptions = expresswinston$LoggerOptionsWithTransports;
-
-    declare function expresswinston$logger(
-        options: expresswinston$LoggerOptions,
-    ): express$Handler;
-
-    declare interface expresswinston$BaseErrorLoggerOptions {
-        level?: string;
-    }
-
-    declare type expresswinston$ErrorLoggerOptionsWithTransports = {
-        transports?: Array<$winstonTransport>,
-        ...
-    } & expresswinston$BaseErrorLoggerOptions;
-
-    declare type expresswinston$ErrorLoggerOptions = expresswinston$ErrorLoggerOptionsWithTransports;
-    declare function expresswinston$errorLogger(
-        options: expresswinston$ErrorLoggerOptions,
-    ): express$ErrorRequestHandler;
-
-    declare module.exports: {
-        logger: typeof expresswinston$logger,
-        errorLogger: typeof expresswinston$errorLogger,
-    };
-}
diff --git a/flow-typed/superagent.js b/flow-typed/superagent.js
deleted file mode 100644
index fff0bc0d..00000000
--- a/flow-typed/superagent.js
+++ /dev/null
@@ -1,308 +0,0 @@
-// @flow
-declare type superagent$CallbackHandler = (
-    err: any,
-    res: ?superagent$Response,
-) => ?boolean;
-
-declare type superagent$Serializer = (obj: any) => string;
-
-declare type superagent$BrowserParser = (str: string) => any;
-
-declare type superagent$NodeParser = (
-    res: superagent$Response,
-    callback: (err: Error | null, body: any) => void,
-) => void;
-
-declare type superagent$Parser =
-    | superagent$BrowserParser
-    | superagent$NodeParser;
-
-declare type superagent$MultipartValueSingle =
-    | Blob
-    | Buffer
-    | stream$Readable
-    | string
-    | boolean
-    | number;
-
-declare type superagent$MultipartValue =
-    | superagent$MultipartValueSingle
-    | superagent$MultipartValueSingle[];
-
-declare interface superagent$SuperAgentRequest extends superagent$Request {
-    agent<+SocketT = net$Socket>(
-        agent?: http$Agent<SocketT>,
-    ): superagent$SuperAgentRequest;
-}
-
-declare type cookiejar$CookieJar = $FlowFixMe;
-
-declare interface superagent$SuperAgentStatic extends stream$Stream {
-    (url: string): superagent$SuperAgentRequest;
-    (method: string, url: string): superagent$SuperAgentRequest;
-
-    agent(): superagent$SuperAgentStatic & superagent$Request;
-    serialize: {[type: string]: superagent$Serializer};
-    parse: {[type: string]: superagent$Parser};
-
-    jar: cookiejar$CookieJar;
-    attachCookies(req: superagent$SuperAgentRequest): void;
-    checkout(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    connect(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    copy(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    del(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    delete(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    get(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    head(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    lock(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    merge(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    mkactivity(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    mkcol(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    move(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    notify(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    options(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    patch(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    post(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    propfind(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    proppatch(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    purge(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    put(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    report(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    saveCookies(res: superagent$Response): void;
-    search(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    subscribe(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    trace(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    unlock(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-    unsubscribe(
-        url: string,
-        callback?: superagent$CallbackHandler,
-    ): superagent$SuperAgentRequest;
-}
-
-declare interface superagent$HTTPError extends Error {
-    status: number;
-    text: string;
-    method: string;
-    path: string;
-}
-
-declare interface superagent$Response extends stream$Readable {
-    accepted: boolean;
-    badRequest: boolean;
-    body: any;
-    charset: string;
-    clientError: boolean;
-    error: false | superagent$HTTPError;
-    files: any;
-    forbidden: boolean;
-    get(header: string): string;
-    get(header: "Set-Cookie"): string[];
-    header: any;
-    info: boolean;
-    links: {...};
-    noContent: boolean;
-    notAcceptable: boolean;
-    notFound: boolean;
-    ok: boolean;
-    redirect: boolean;
-    serverError: boolean;
-    status: number;
-    statusType: number;
-    text: string;
-    type: string;
-    unauthorized: boolean;
-    xhr: XMLHttpRequest;
-    redirects: string[];
-}
-
-declare interface superagent$Request extends Promise<superagent$Response> {
-    cookies: string;
-    method: string;
-    url: string;
-    abort(): void;
-    accept(type: string): superagent$Request;
-    attach(
-        field: string,
-        file: superagent$MultipartValueSingle,
-        options?: string | {filename?: string, contentType?: string},
-    ): superagent$Request;
-    auth(
-        user: string,
-        pass: string,
-        options?: {type: "basic" | "auto"},
-    ): superagent$Request;
-    auth(token: string, options: {type: "bearer"}): superagent$Request;
-    buffer(val?: boolean): superagent$Request;
-    ca(cert: string | string[] | Buffer | Buffer[]): superagent$Request;
-    cert(cert: string | string[] | Buffer | Buffer[]): superagent$Request;
-    clearTimeout(): superagent$Request;
-    disableTLSCerts(): superagent$Request;
-    end(callback?: superagent$CallbackHandler): void;
-    field(name: string, val: superagent$MultipartValue): superagent$Request;
-    field(fields: {
-        [fieldName: string]: superagent$MultipartValue,
-    }): superagent$Request;
-    get(field: string): string;
-    key(cert: string | string[] | Buffer | Buffer[]): superagent$Request;
-    ok(callback: (res: superagent$Response) => boolean): superagent$Request;
-    on(name: "error", handler: (err: any) => void): superagent$Request;
-    on(
-        name: "progress",
-        handler: (event: superagent$ProgressEvent) => void,
-    ): superagent$Request;
-    on(
-        name: "response",
-        handler: (response: superagent$Response) => void,
-    ): superagent$Request;
-    on(name: string, handler: (event: any) => void): superagent$Request;
-    parse(parser: superagent$Parser): superagent$Request;
-    part(): superagent$Request;
-    pfx(
-        cert:
-            | string
-            | string[]
-            | Buffer
-            | Buffer[]
-            | {pfx: string | Buffer, passphrase: string},
-    ): superagent$Request;
-    pipe(stream: stream$Writable, options?: {...}): stream$Writable;
-    query(val: {...} | string): superagent$Request;
-    redirects(n: number): superagent$Request;
-    responseType(type: string): superagent$Request;
-    retry(
-        count?: number,
-        callback?: superagent$CallbackHandler,
-    ): superagent$Request;
-    send(data?: string | {...}): superagent$Request;
-    serialize(serializer: superagent$Serializer): superagent$Request;
-    set(field: {...}): superagent$Request;
-    set(field: string, val: string): superagent$Request;
-    set(field: "Cookie", val: string[]): superagent$Request;
-    timeout(
-        ms: number | {deadline?: number, response?: number},
-    ): superagent$Request;
-    trustLocalhost(enabled?: boolean): superagent$Request;
-    type(val: string): superagent$Request;
-    unset(field: string): superagent$Request;
-    use(fn: superagent$Plugin): superagent$Request;
-    withCredentials(): superagent$Request;
-    write(data: string | Buffer, encoding?: string): superagent$Request;
-    maxResponseSize(size: number): superagent$Request;
-
-    /**
-     * Added by superagent-cache-plugin
-     */
-    cacheWhenEmpty(cacheWhenEmpty: boolean): superagent$Response;
-    doQuery(doQuery: boolean): superagent$Request;
-    expiration(expiration: ?number): superagent$Request;
-    forceUpdate(forceUpdate: ?boolean): superagent$Request;
-    pruneQuery(pruneQuery: Array<string>): superagent$Request;
-    pruneHeader(pruneHeader: Array<string>): superagent$Request;
-    prune(
-        prune: (
-            response: superagent$Response,
-            gutResponse: (superagent$Response) => any,
-        ) => any,
-    ): superagent$Request;
-    responseProp(responseProp: string): superagent$Request;
-}
-
-declare type superagent$Plugin = (req: superagent$SuperAgentRequest) => void;
-
-declare type superagent$ProgressEvent = {
-    direction: "download" | "upload",
-    loaded: number,
-    percent?: number,
-    total?: number,
-};
-
-declare module "superagent" {
-    declare export type CallbackHandler = superagent$CallbackHandler;
-    declare export type Serializer = superagent$Serializer;
-    declare export type BrowserParser = superagent$BrowserParser;
-    declare export type NodeParser = superagent$NodeParser;
-    declare export type Parser = superagent$Parser;
-    declare export type MultipartValueSingle = superagent$MultipartValueSingle;
-    declare export type MultipartValue = superagent$MultipartValue;
-    declare export type Response = superagent$Response;
-    declare export type SuperAgentRequest = superagent$SuperAgentRequest;
-    declare export type Request = superagent$Request;
-    declare export type Plugin = superagent$Plugin;
-
-    declare module.exports: superagent$SuperAgentStatic;
-}
diff --git a/packages/eslint-config-khan/.prettierrc.js b/packages/eslint-config-khan/.prettierrc.js
index 453b9c46..5c735889 100644
--- a/packages/eslint-config-khan/.prettierrc.js
+++ b/packages/eslint-config-khan/.prettierrc.js
@@ -1,5 +1,4 @@
 /* eslint-disable import/no-commonjs */
-// @flow
 module.exports = {
     printWidth: 80,
     tabWidth: 4,
diff --git a/packages/wonder-stuff-core/src/__tests__/__snapshots__/build-caused-by-message.test.js.snap b/packages/wonder-stuff-core/src/__tests__/__snapshots__/build-caused-by-message.test.ts.snap
similarity index 100%
rename from packages/wonder-stuff-core/src/__tests__/__snapshots__/build-caused-by-message.test.js.snap
rename to packages/wonder-stuff-core/src/__tests__/__snapshots__/build-caused-by-message.test.ts.snap
diff --git a/packages/wonder-stuff-core/src/__tests__/__snapshots__/errors-from-error.test.js.snap b/packages/wonder-stuff-core/src/__tests__/__snapshots__/errors-from-error.test.ts.snap
similarity index 100%
rename from packages/wonder-stuff-core/src/__tests__/__snapshots__/errors-from-error.test.js.snap
rename to packages/wonder-stuff-core/src/__tests__/__snapshots__/errors-from-error.test.ts.snap
diff --git a/packages/wonder-stuff-core/src/__tests__/__snapshots__/kind-error.test.js.snap b/packages/wonder-stuff-core/src/__tests__/__snapshots__/kind-error.test.ts.snap
similarity index 100%
rename from packages/wonder-stuff-core/src/__tests__/__snapshots__/kind-error.test.js.snap
rename to packages/wonder-stuff-core/src/__tests__/__snapshots__/kind-error.test.ts.snap
diff --git a/packages/wonder-stuff-core/src/__tests__/build-caused-by-message.test.js b/packages/wonder-stuff-core/src/__tests__/build-caused-by-message.test.ts
similarity index 95%
rename from packages/wonder-stuff-core/src/__tests__/build-caused-by-message.test.js
rename to packages/wonder-stuff-core/src/__tests__/build-caused-by-message.test.ts
index 9a0c1730..ab19d3da 100644
--- a/packages/wonder-stuff-core/src/__tests__/build-caused-by-message.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/build-caused-by-message.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {buildCausedByMessage} from "../build-caused-by-message";
 
 describe("#buildCausedByMessage", () => {
@@ -20,7 +19,7 @@ describe("#buildCausedByMessage", () => {
 
     it.each([null, undefined])(
         "should only include cause if it is non-null",
-        (testCase) => {
+        (testCase: any) => {
             // Arrange
             const consequence = "No more Halloween candy";
             const cause = testCase;
@@ -35,7 +34,7 @@ describe("#buildCausedByMessage", () => {
 
     it.each([null, undefined])(
         "should default nullish consequences to (empty message)",
-        (testCase) => {
+        (testCase: any) => {
             // Arrange
             const consequence = testCase;
             const cause = null;
@@ -50,7 +49,7 @@ describe("#buildCausedByMessage", () => {
 
     it.each(["    ", "\n\t\t"])(
         "should default whitespace strings to (empty message)",
-        (testCase) => {
+        (testCase: any) => {
             // Arrange
             const consequence = testCase;
             const cause = testCase;
diff --git a/packages/wonder-stuff-core/src/__tests__/clone-metadata.test.js b/packages/wonder-stuff-core/src/__tests__/clone-metadata.test.ts
similarity index 67%
rename from packages/wonder-stuff-core/src/__tests__/clone-metadata.test.js
rename to packages/wonder-stuff-core/src/__tests__/clone-metadata.test.ts
index fea6cc20..0c21b0dc 100644
--- a/packages/wonder-stuff-core/src/__tests__/clone-metadata.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/clone-metadata.test.ts
@@ -1,10 +1,9 @@
-// @flow
 import {cloneMetadata} from "../clone-metadata";
 
 describe("#cloneMetadata", () => {
     it.each([undefined, null])(
         "should return the metadata when it is %s",
-        (value) => {
+        (value: any) => {
             // Arrange
 
             // Act
@@ -34,15 +33,19 @@ describe("#cloneMetadata", () => {
             boolean: "true",
             undefined: undefined,
             null: null,
-        };
+        } as const;
 
         // Act
         const result = cloneMetadata(metadata);
+        // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'string' because it is a read-only property.
         metadata.string = "baz";
+        // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'number' because it is a read-only property.
         metadata.number = "43";
+        // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'boolean' because it is a read-only property.
         metadata.boolean = "false";
+        // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'undefined' because it is a read-only property.
         metadata.undefined = "foo";
-        // $FlowIgnore[incompatible-type]
+        // @ts-expect-error [FEI-5011] - TS2704 - The operand of a 'delete' operator cannot be a read-only property. | TS2790 - The operand of a 'delete' operator must be optional.
         delete metadata.null;
 
         // Assert
@@ -60,10 +63,12 @@ describe("#cloneMetadata", () => {
         // Arrange
         const metadata = {
             array: [1, 2, 3],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly array: readonly [1, 2, 3]; }' is not assignable to parameter of type 'Readonly<Metadata>'.
         const result = cloneMetadata(metadata);
+        // @ts-expect-error [FEI-5011] - TS2339 - Property 'push' does not exist on type 'readonly [1, 2, 3]'.
         metadata.array.push(4);
 
         // Assert
@@ -80,10 +85,11 @@ describe("#cloneMetadata", () => {
                 a: 1,
                 b: 2,
             },
-        };
+        } as const;
 
         // Act
         const result = cloneMetadata(metadata);
+        // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'a' because it is a read-only property.
         metadata.object.a = 3;
 
         // Assert
@@ -113,10 +119,12 @@ describe("#cloneMetadata", () => {
                     ],
                 },
             },
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly object: { readonly a: 1; readonly b: 2; readonly c: { readonly d: 3; readonly e: readonly [4, 5, { readonly nested: "in here"; }]; }; }; }' is not assignable to parameter of type 'Readonly<Metadata>'.
         const result = cloneMetadata(metadata);
+        // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'nested' because it is a read-only property.
         metadata.object.c.e[2].nested = "in there";
 
         // Assert
diff --git a/packages/wonder-stuff-core/src/__tests__/clone.test.js b/packages/wonder-stuff-core/src/__tests__/clone.test.ts
similarity index 95%
rename from packages/wonder-stuff-core/src/__tests__/clone.test.js
rename to packages/wonder-stuff-core/src/__tests__/clone.test.ts
index d1c402fc..17e336a6 100644
--- a/packages/wonder-stuff-core/src/__tests__/clone.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/clone.test.ts
@@ -1,10 +1,9 @@
-// @flow
 import {clone} from "../clone";
 
 describe("#clone", () => {
     it.each([undefined, null])(
         "should return the value when it is %s",
-        (value) => {
+        (value: any) => {
             // Arrange
 
             // Act
@@ -23,7 +22,7 @@ describe("#clone", () => {
             boolean: "true",
             undefined: undefined,
             null: null,
-        };
+        } as const;
 
         // Act
         const result = clone(originalValue);
@@ -37,7 +36,7 @@ describe("#clone", () => {
         // Arrange
         const originalValue = {
             array: [1, 2, 3],
-        };
+        } as const;
 
         // Act
         const result = clone(originalValue);
@@ -54,7 +53,7 @@ describe("#clone", () => {
                 a: 1,
                 b: 2,
             },
-        };
+        } as const;
 
         // Act
         const result = clone(originalValue);
@@ -81,7 +80,7 @@ describe("#clone", () => {
                     ],
                 },
             },
-        };
+        } as const;
 
         // Act
         const result = clone(originalValue);
diff --git a/packages/wonder-stuff-core/src/__tests__/entries.flowtest.js b/packages/wonder-stuff-core/src/__tests__/entries.flowtest.ts
similarity index 70%
rename from packages/wonder-stuff-core/src/__tests__/entries.flowtest.js
rename to packages/wonder-stuff-core/src/__tests__/entries.flowtest.ts
index e47ebd75..6dfba467 100644
--- a/packages/wonder-stuff-core/src/__tests__/entries.flowtest.js
+++ b/packages/wonder-stuff-core/src/__tests__/entries.flowtest.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module '../entries' or its corresponding type declarations.
 import {entries} from "../entries";
 
 {
@@ -7,12 +7,12 @@ import {entries} from "../entries";
         a: 1,
         b: "2",
         c: [3, 4],
-    };
+    } as const;
 
     const entries1 = entries(obj1);
 
     // This works because the keys are all strings
-    const [_]: [string, mixed] = entries1[0];
+    const [_]: [string, unknown] = entries1[0];
 }
 
 {
@@ -21,16 +21,15 @@ import {entries} from "../entries";
         a: 1,
         b: "2",
         c: [3, 4],
-    };
+    } as const;
     const entries2 = entries(obj2);
 
     // This works because the returned tuple type is of a supertype of all key
     // names and the value type (which we don't care about for this flow check).
-    const [_]: ["a" | "b" | "c", mixed] = entries2[0];
+    const [_]: ["a" | "b" | "c", unknown] = entries2[0];
 
     // This errors because we try to get a key of only one type.
-    // $FlowExpectedError[incompatible-type]
-    const [__]: ["a", mixed] = entries2[0];
+    const [__]: ["a", unknown] = entries2[0];
 }
 
 {
@@ -39,7 +38,7 @@ import {entries} from "../entries";
         a: 1,
         b: "2",
         c: [3, 4],
-    };
+    } as const;
 
     const entries1 = entries(obj1);
 
@@ -48,14 +47,15 @@ import {entries} from "../entries";
     const [_, __]: [string, number | string | Array<number>] = entries1[0];
 
     // This errors because not all values are a number.
-    // $FlowExpectedError[incompatible-type]
     const [___, ____]: [string, number] = entries1[0];
 }
 
 {
     // should work with class instances
     class Foo {
+        // @ts-expect-error [FEI-5011] - TS2564 - Property 'a' has no initializer and is not definitely assigned in the constructor.
         a: string;
+        // @ts-expect-error [FEI-5011] - TS2564 - Property 'b' has no initializer and is not definitely assigned in the constructor.
         b: string;
     }
     const foo = new Foo();
diff --git a/packages/wonder-stuff-core/src/__tests__/entries.test.js b/packages/wonder-stuff-core/src/__tests__/entries.test.ts
similarity index 85%
rename from packages/wonder-stuff-core/src/__tests__/entries.test.js
rename to packages/wonder-stuff-core/src/__tests__/entries.test.ts
index 5503d947..51e56aa6 100644
--- a/packages/wonder-stuff-core/src/__tests__/entries.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/entries.test.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module '../entries' or its corresponding type declarations.
 import {entries} from "../entries";
 
 describe("#entries", () => {
@@ -9,7 +9,7 @@ describe("#entries", () => {
             a: 1,
             b: "2",
             c: [3, 4],
-        };
+        } as const;
 
         // Act
         entries(obj);
@@ -24,7 +24,7 @@ describe("#entries", () => {
             a: 1,
             b: "2",
             c: [3, 4],
-        };
+        } as const;
         jest.spyOn(Object, "entries").mockReturnValueOnce([
             ["e", 1],
             ["f", 2],
diff --git a/packages/wonder-stuff-core/src/__tests__/error-info.test.js b/packages/wonder-stuff-core/src/__tests__/error-info.test.ts
similarity index 92%
rename from packages/wonder-stuff-core/src/__tests__/error-info.test.js
rename to packages/wonder-stuff-core/src/__tests__/error-info.test.ts
index 0a570e86..52926169 100644
--- a/packages/wonder-stuff-core/src/__tests__/error-info.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/error-info.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as BuildCausedByMessage from "../build-caused-by-message";
 import {ErrorInfo} from "../error-info";
 
@@ -77,6 +76,7 @@ describe("ErrorInfo", () => {
                 // Act
                 const act = () =>
                     // $FlowIgnore[incompatible-call]
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'null' is not assignable to parameter of type 'ErrorInfo'.
                     ErrorInfo.fromConsequenceAndCause(null, cause);
 
                 // Assert
@@ -96,6 +96,7 @@ describe("ErrorInfo", () => {
                 // Act
                 const act = () =>
                     // $FlowIgnore[incompatible-call]
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'null' is not assignable to parameter of type 'ErrorInfo'.
                     ErrorInfo.fromConsequenceAndCause(consequence, null);
 
                 // Assert
@@ -134,6 +135,7 @@ describe("ErrorInfo", () => {
                 // Act
                 const act = () =>
                     // $FlowIgnore[incompatible-call]
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'null' is not assignable to parameter of type 'ErrorInfo'.
                     ErrorInfo.fromConsequenceAndCause(null, cause);
 
                 // Assert
@@ -153,6 +155,7 @@ describe("ErrorInfo", () => {
                 // Act
                 const act = () =>
                     // $FlowIgnore[incompatible-call]
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'null' is not assignable to parameter of type 'ErrorInfo'.
                     ErrorInfo.fromConsequenceAndCause(consequence, null);
 
                 // Assert
@@ -260,7 +263,7 @@ describe("ErrorInfo", () => {
         describe("when not built for production", () => {
             it("should throw if error is not an Error", () => {
                 // Arrange
-                // $FlowIgnore[incompatible-type]
+                // @ts-expect-error [FEI-5011] - TS2739 - Type '{}' is missing the following properties from type 'Error': name, message
                 const error: Error = {};
 
                 // Act
@@ -306,7 +309,7 @@ describe("ErrorInfo", () => {
 
             it("should not throw if error is not an Error", () => {
                 // Arrange
-                // $FlowIgnore[incompatible-type]
+                // @ts-expect-error [FEI-5011] - TS2739 - Type '{}' is missing the following properties from type 'Error': name, message
                 const error: Error = {};
 
                 // Act
@@ -395,6 +398,7 @@ describe("ErrorInfo", () => {
             // Arrange
             const error = new Error("test");
             const stackAndToString = "Error: test\nframe1\nframe2\nframe3";
+            // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call. | TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'.
             jest.spyOn(error, "toString").mockReturnValue(stackAndToString);
             error.stack = stackAndToString;
 
@@ -413,7 +417,6 @@ describe("ErrorInfo", () => {
         it("should create an empty stack array if there is no stack", () => {
             // Arrange
             const error = new Error("test");
-            // $FlowIgnore[incompatible-type]
             delete error.stack;
 
             // Act
@@ -428,7 +431,7 @@ describe("ErrorInfo", () => {
         describe("when not built for production", () => {
             it("should throw if error is not an Error", () => {
                 // Arrange
-                // $FlowIgnore[incompatible-type]
+                // @ts-expect-error [FEI-5011] - TS2739 - Type '{}' is missing the following properties from type 'Error': name, message
                 const error: Error = {};
 
                 // Act
@@ -448,7 +451,7 @@ describe("ErrorInfo", () => {
 
             it("should not throw if error is not an Error", () => {
                 // Arrange
-                // $FlowIgnore[incompatible-type]
+                // @ts-expect-error [FEI-5011] - TS2739 - Type '{}' is missing the following properties from type 'Error': name, message
                 const error: Error = {};
 
                 // Act
@@ -502,6 +505,7 @@ describe("ErrorInfo", () => {
             // Arrange
             const error = new Error("test");
             const stackAndToString = "Error: test\nframe1\nframe2\nframe3";
+            // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call. | TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'.
             jest.spyOn(error, "toString").mockReturnValue(stackAndToString);
             error.stack = stackAndToString;
 
@@ -520,7 +524,6 @@ describe("ErrorInfo", () => {
         it("should create an empty stack array if there is no stack", () => {
             // Arrange
             const error = new Error("test");
-            // $FlowIgnore[incompatible-type]
             delete error.stack;
 
             // Act
diff --git a/packages/wonder-stuff-core/src/__tests__/errors-from-error.test.js b/packages/wonder-stuff-core/src/__tests__/errors-from-error.test.ts
similarity index 83%
rename from packages/wonder-stuff-core/src/__tests__/errors-from-error.test.js
rename to packages/wonder-stuff-core/src/__tests__/errors-from-error.test.ts
index ef8c4ca5..9f7f333f 100644
--- a/packages/wonder-stuff-core/src/__tests__/errors-from-error.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/errors-from-error.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError} from "../kind-error";
 import {errorsFromError, Order} from "../errors-from-error";
 
@@ -7,11 +6,12 @@ import type {Options as KindErrorOptions} from "../kind-error";
 describe("#errorsFromError", () => {
     it.each([null, undefined, "NOT_A_GOOD_VALUE", 42])(
         "should throw if the order is invalid",
-        (testCase) => {
+        (testCase: any) => {
             // Arrange
             const error = new Error("test");
 
             // Act
+            // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call.
             const act = () => Array.from(errorsFromError(error, testCase));
 
             // Assert
@@ -21,15 +21,17 @@ describe("#errorsFromError", () => {
 
     it.each([null, undefined])(
         "should yield an empty sequence if the error is nullish",
-        (error) => {
+        (error: any) => {
             // Arrange
 
             // Act
             const result = Array.from(
+                // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call.
                 errorsFromError(error, Order.ConsequenceFirst),
             );
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeEmpty' does not exist on type 'JestMatchers<unknown[]>'.
             expect(result).toBeEmpty();
         },
     );
@@ -40,6 +42,7 @@ describe("#errorsFromError", () => {
 
         // Act
         const result = Array.from(
+            // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call.
             errorsFromError(error, Order.ConsequenceFirst),
         );
 
@@ -64,6 +67,7 @@ describe("#errorsFromError", () => {
 
             // Act
             const result = Array.from(
+                // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call.
                 errorsFromError(rootError, Order.ConsequenceFirst),
             );
 
@@ -89,6 +93,7 @@ describe("#errorsFromError", () => {
 
             // Act
             const result = Array.from(
+                // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call.
                 errorsFromError(rootError, Order.CauseFirst),
             );
 
diff --git a/packages/wonder-stuff-core/src/__tests__/errors.test.js b/packages/wonder-stuff-core/src/__tests__/errors.test.ts
similarity index 61%
rename from packages/wonder-stuff-core/src/__tests__/errors.test.js
rename to packages/wonder-stuff-core/src/__tests__/errors.test.ts
index f7150601..47e4e7fd 100644
--- a/packages/wonder-stuff-core/src/__tests__/errors.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/errors.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors} from "../errors";
 
 describe("Errors", () => {
@@ -9,6 +8,7 @@ describe("Errors", () => {
         const result = Object.isFrozen(Errors);
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeTrue' does not exist on type 'JestMatchers<boolean>'.
         expect(result).toBeTrue();
     });
 
@@ -17,10 +17,11 @@ describe("Errors", () => {
 
         // Act
         const result = Object.values(Errors).every(
-            (v) => typeof v === "string",
+            (v: any) => typeof v === "string",
         );
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeTrue' does not exist on type 'JestMatchers<boolean>'.
         expect(result).toBeTrue();
     });
 });
diff --git a/packages/wonder-stuff-core/src/__tests__/get-kind-from-error.test.js b/packages/wonder-stuff-core/src/__tests__/get-kind-from-error.test.ts
similarity index 96%
rename from packages/wonder-stuff-core/src/__tests__/get-kind-from-error.test.js
rename to packages/wonder-stuff-core/src/__tests__/get-kind-from-error.test.ts
index d4b48d6e..9844f677 100644
--- a/packages/wonder-stuff-core/src/__tests__/get-kind-from-error.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/get-kind-from-error.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors} from "../errors";
 import {getKindFromError} from "../get-kind-from-error";
 import {KindError} from "../kind-error";
@@ -6,7 +5,7 @@ import {KindError} from "../kind-error";
 describe("#getKindFromError", () => {
     it.each([null, undefined, new Error("test")])(
         "should return Errors.Unknown for a non-KindError value like %s",
-        (error) => {
+        (error: any) => {
             // Arrange
 
             // Act
diff --git a/packages/wonder-stuff-core/src/__tests__/get-original-stack-from-error.test.js b/packages/wonder-stuff-core/src/__tests__/get-original-stack-from-error.test.ts
similarity index 99%
rename from packages/wonder-stuff-core/src/__tests__/get-original-stack-from-error.test.js
rename to packages/wonder-stuff-core/src/__tests__/get-original-stack-from-error.test.ts
index 2e717a41..6b22275f 100644
--- a/packages/wonder-stuff-core/src/__tests__/get-original-stack-from-error.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/get-original-stack-from-error.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {getOriginalStackFromError} from "../get-original-stack-from-error";
 import {KindError} from "../kind-error";
 
diff --git a/packages/wonder-stuff-core/src/__tests__/keys.flowtest.js b/packages/wonder-stuff-core/src/__tests__/keys.flowtest.ts
similarity index 71%
rename from packages/wonder-stuff-core/src/__tests__/keys.flowtest.js
rename to packages/wonder-stuff-core/src/__tests__/keys.flowtest.ts
index b096648c..7ebfe77b 100644
--- a/packages/wonder-stuff-core/src/__tests__/keys.flowtest.js
+++ b/packages/wonder-stuff-core/src/__tests__/keys.flowtest.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module '../keys' or its corresponding type declarations.
 import {keys} from "../keys";
 
 {
@@ -6,7 +6,7 @@ import {keys} from "../keys";
     const obj1 = {
         a: 1,
         b: "2",
-    };
+    } as const;
 
     const keys1 = keys(obj1);
     const _: string = keys1[0];
@@ -18,7 +18,7 @@ import {keys} from "../keys";
         a: 1,
         b: "2",
         c: [3, 4],
-    };
+    } as const;
 
     // This works because the return type is an array of a supertype of all key
     // names, thanks to $Keys<>.
@@ -28,14 +28,15 @@ import {keys} from "../keys";
     // This errors because we try to get a key of only one type. Flow sees this
     // as a bad call rather than a bad assignment. Hence the expectation on
     // the callsite, not the assignment.
-    // $FlowExpectedError[incompatible-call]
     const keys2bad = keys(obj2);
     const __: "a" = keys2bad[0];
 }
 
 {
     // should work with more specific object types
-    const obj3: {|[string]: string|} = {
+    const obj3: {
+        [key: string]: string;
+    } = {
         a: "1",
         b: "2",
     };
@@ -47,7 +48,9 @@ import {keys} from "../keys";
 {
     // should work with class instances
     class Foo {
+        // @ts-expect-error [FEI-5011] - TS2564 - Property 'a' has no initializer and is not definitely assigned in the constructor.
         a: string;
+        // @ts-expect-error [FEI-5011] - TS2564 - Property 'b' has no initializer and is not definitely assigned in the constructor.
         b: string;
     }
     const foo = new Foo();
diff --git a/packages/wonder-stuff-core/src/__tests__/keys.test.js b/packages/wonder-stuff-core/src/__tests__/keys.test.ts
similarity index 72%
rename from packages/wonder-stuff-core/src/__tests__/keys.test.js
rename to packages/wonder-stuff-core/src/__tests__/keys.test.ts
index 25149893..844d2fd5 100644
--- a/packages/wonder-stuff-core/src/__tests__/keys.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/keys.test.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module '../keys' or its corresponding type declarations.
 import {keys} from "../keys";
 
 describe("#keys", () => {
@@ -9,7 +9,7 @@ describe("#keys", () => {
             a: 1,
             b: "2",
             c: [3, 4],
-        };
+        } as const;
 
         // Act
         keys(obj);
@@ -24,7 +24,8 @@ describe("#keys", () => {
             a: 1,
             b: "2",
             c: [3, 4],
-        };
+        } as const;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'string[]'.
         jest.spyOn(Object, "keys").mockReturnValueOnce("THE RESULT");
 
         // Act
diff --git a/packages/wonder-stuff-core/src/__tests__/kind-error.test.js b/packages/wonder-stuff-core/src/__tests__/kind-error.test.ts
similarity index 94%
rename from packages/wonder-stuff-core/src/__tests__/kind-error.test.js
rename to packages/wonder-stuff-core/src/__tests__/kind-error.test.ts
index 1818209d..95051747 100644
--- a/packages/wonder-stuff-core/src/__tests__/kind-error.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/kind-error.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as CloneMetadata from "../clone-metadata";
 import {ErrorInfo} from "../error-info";
 import {Errors} from "../errors";
@@ -64,6 +63,7 @@ describe("KindError", () => {
             const error = new KindError("MESSAGE");
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toEndWith' does not exist on type 'JestMatchers<string>'.
             expect(error.name).toEndWith("Error");
         });
 
@@ -76,13 +76,14 @@ describe("KindError", () => {
             });
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toEndWith' does not exist on type 'JestMatchers<string>'.
             expect(error.name).toEndWith("CUSTOM_NAMEError");
         });
 
         describe("when not built for production", () => {
             it.each(["N A M E", "NA\nME"])(
                 "should throw if the name has whitespace like %s",
-                (name) => {
+                (name: any) => {
                     // Arrange
 
                     // Act
@@ -96,7 +97,7 @@ describe("KindError", () => {
 
             it.each(["K I N D", "KI\nND"])(
                 "should throw if the kind has whitespace like %s",
-                (kind) => {
+                (kind: any) => {
                     // Arrange
 
                     // Act
@@ -109,7 +110,7 @@ describe("KindError", () => {
 
             it.each(["P R E F I X", "PRE\nFIX"])(
                 "should throw if the prefix has whitespace like %s",
-                (prefix) => {
+                (prefix: any) => {
                     // Arrange
 
                     // Act
@@ -159,7 +160,7 @@ describe("KindError", () => {
 
             it.each(["N A M E", "NA\nME"])(
                 "should not throw validation error if the name has whitespace like %s",
-                (name) => {
+                (name: any) => {
                     // Arrange
 
                     // Act
@@ -175,7 +176,7 @@ describe("KindError", () => {
 
             it.each(["K I N D", "KI\nND"])(
                 "should not throw validation error if the kind has whitespace like %s",
-                (kind) => {
+                (kind: any) => {
                     // Arrange
 
                     // Act
@@ -190,7 +191,7 @@ describe("KindError", () => {
 
             it.each(["P R E F I X", "PRE\nFIX"])(
                 "should not throw validation error if the prefix has whitespace like %s",
-                (prefix) => {
+                (prefix: any) => {
                     // Arrange
 
                     // Act
@@ -235,9 +236,10 @@ describe("KindError", () => {
             // Arrange
             const metadata = {
                 foo: "bar",
-            };
+            } as const;
             const cloneMetadataSpy = jest
                 .spyOn(CloneMetadata, "cloneMetadata")
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '"CLONED_METADATA"' is not assignable to parameter of type 'Readonly<Metadata> | null | undefined'.
                 .mockReturnValue("CLONED_METADATA");
 
             // Act
@@ -307,6 +309,7 @@ describe("KindError", () => {
                     const act = () =>
                         new KindError("MESSAGE", Errors.Unknown, {
                             // $FlowIgnore[incompatible-call]
+                            // @ts-expect-error [FEI-5011] - TS2322 - Type 'string' is not assignable to type 'Error | null | undefined'.
                             cause: "NOT_AN_ERROR",
                         });
 
@@ -329,6 +332,7 @@ describe("KindError", () => {
                     const act = () =>
                         new KindError("MESSAGE", Errors.Unknown, {
                             // $FlowIgnore[incompatible-call]
+                            // @ts-expect-error [FEI-5011] - TS2322 - Type 'string' is not assignable to type 'Error | null | undefined'.
                             cause: "NOT_AN_ERROR",
                         });
 
@@ -464,7 +468,7 @@ describe("KindError", () => {
 
             describe.each([undefined, null, false])(
                 "when composite stack is %s",
-                (compositeStackValue) => {
+                (compositeStackValue: any) => {
                     it("should set the stack to the normalized stack, not the combined stack", () => {
                         // Arrange
                         const normalizedErrorInfo = new ErrorInfo(
diff --git a/packages/wonder-stuff-core/src/__tests__/safe-stringify.test.js b/packages/wonder-stuff-core/src/__tests__/safe-stringify.test.ts
similarity index 87%
rename from packages/wonder-stuff-core/src/__tests__/safe-stringify.test.js
rename to packages/wonder-stuff-core/src/__tests__/safe-stringify.test.ts
index 71832c34..3c149b70 100644
--- a/packages/wonder-stuff-core/src/__tests__/safe-stringify.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/safe-stringify.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {safeStringify} from "../safe-stringify";
 
 describe("#safeStringify", () => {
@@ -8,7 +7,7 @@ describe("#safeStringify", () => {
             const value = {
                 a: 1,
                 b: 2,
-            };
+            } as const;
 
             // Act
             const result = safeStringify(value);
@@ -21,7 +20,7 @@ describe("#safeStringify", () => {
     describe("with default value argument", () => {
         it.each([null, undefined])(
             "should return the default for nullish values",
-            (value) => {
+            (value: any) => {
                 // Arrange
                 const defaultValue = "default";
 
@@ -50,6 +49,7 @@ describe("#safeStringify", () => {
         it("should return the default if JSON.stringify returns a nullish value", () => {
             // Arrange
             const defaultValue = "default";
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'undefined' is not assignable to parameter of type 'string'.
             jest.spyOn(JSON, "stringify").mockReturnValue(undefined);
 
             // Act
@@ -63,11 +63,11 @@ describe("#safeStringify", () => {
     describe("with options argument", () => {
         it.each([null, undefined])(
             "should return the default for nullish values",
-            (value) => {
+            (value: any) => {
                 // Arrange
                 const options = {
                     defaultValue: "default",
-                };
+                } as const;
 
                 // Act
                 const result = safeStringify(value, options);
@@ -81,7 +81,7 @@ describe("#safeStringify", () => {
             // Arrange
             const options = {
                 defaultValue: "default",
-            };
+            } as const;
             jest.spyOn(JSON, "stringify").mockImplementation(() => {
                 throw new Error("error");
             });
@@ -97,7 +97,8 @@ describe("#safeStringify", () => {
             // Arrange
             const options = {
                 defaultValue: "default",
-            };
+            } as const;
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'undefined' is not assignable to parameter of type 'string'.
             jest.spyOn(JSON, "stringify").mockReturnValue(undefined);
 
             // Act
@@ -109,7 +110,7 @@ describe("#safeStringify", () => {
 
         it("should not pretty format if the indent option is not given", () => {
             // Arrange
-            const options = {};
+            const options: Record<string, any> = {};
 
             // Act
             const result = safeStringify({field: 1}, options);
@@ -120,11 +121,11 @@ describe("#safeStringify", () => {
 
         it.each([null, undefined, 0])(
             "should not pretty format if the indent option is %s",
-            (value) => {
+            (value: any) => {
                 // Arrange
                 const options = {
                     indent: value,
-                };
+                } as const;
 
                 // Act
                 const result = safeStringify({field: 1}, options);
@@ -136,11 +137,11 @@ describe("#safeStringify", () => {
 
         it.each([2, 4])(
             "should pretty format if the indent option is %s",
-            (value) => {
+            (value: any) => {
                 // Arrange
                 const options = {
                     indent: value,
-                };
+                } as const;
                 const expectedIndex = Array(value).fill(" ").join("");
 
                 // Act
diff --git a/packages/wonder-stuff-core/src/__tests__/truncate-middle.test.js b/packages/wonder-stuff-core/src/__tests__/truncate-middle.test.ts
similarity index 96%
rename from packages/wonder-stuff-core/src/__tests__/truncate-middle.test.js
rename to packages/wonder-stuff-core/src/__tests__/truncate-middle.test.ts
index 1cf54926..0a0ca6a0 100644
--- a/packages/wonder-stuff-core/src/__tests__/truncate-middle.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/truncate-middle.test.ts
@@ -1,10 +1,9 @@
-// @flow
 import {truncateMiddle} from "../truncate-middle";
 
 describe("#truncateMiddle", () => {
     it.each(["", "ABCDE", "ABCDEFGH"])(
         "should return the given string if it is less than or equal to given max length",
-        (testPoint) => {
+        (testPoint: any) => {
             // Arrange
 
             // Act
diff --git a/packages/wonder-stuff-core/src/__tests__/values.flowtest.js b/packages/wonder-stuff-core/src/__tests__/values.flowtest.ts
similarity index 73%
rename from packages/wonder-stuff-core/src/__tests__/values.flowtest.js
rename to packages/wonder-stuff-core/src/__tests__/values.flowtest.ts
index dd668f5b..418ac005 100644
--- a/packages/wonder-stuff-core/src/__tests__/values.flowtest.js
+++ b/packages/wonder-stuff-core/src/__tests__/values.flowtest.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module '../values' or its corresponding type declarations.
 import {values} from "../values";
 
 {
@@ -7,7 +7,7 @@ import {values} from "../values";
         a: 1,
         b: "2",
         c: [3, 4],
-    };
+    } as const;
     const obj1Values = values(obj1);
 
     // This works because the variable is typed to all the possible value types.
@@ -15,13 +15,14 @@ import {values} from "../values";
 
     // This errors because the variable is only typed to string, but the value
     // could be a number, string, or array of numbers.
-    // $FlowExpectedError[incompatible-type]
     const __: string = obj1Values[1];
 }
 
 {
     // should work with explicit object-as-map types
-    const map1: {|[string]: number|} = {
+    const map1: {
+        [key: string]: number;
+    } = {
         a: 1,
         b: 2,
         c: 3,
@@ -33,14 +34,13 @@ import {values} from "../values";
 
     // This errors because the variable is typed to string, and that is not
     // a number.
-    // $FlowExpectedError[incompatible-type]
     const __: string = map1Values[1];
 }
 
 {
     // should return type Array<empty> for empty object
-    const emptyObj = {};
-    const _: Array<empty> = values(emptyObj);
+    const emptyObj: Record<string, any> = {};
+    const _: Array<never> = values(emptyObj);
 }
 
 {
@@ -48,21 +48,21 @@ import {values} from "../values";
     const obj2 = {
         a: 1,
         b: "2",
-    };
+    } as const;
 
     // This errors because the return type of values() is not Array<number>
-    // $FlowExpectedError[incompatible-type]
     const _: Array<number> = values(obj2);
 
     // This errors because the object does not have values that are all numbers.
-    // $FlowExpectedError[incompatible-call]
     const __ = values<number>(obj2);
 }
 
 {
     // should work with class instances
     class Foo {
+        // @ts-expect-error [FEI-5011] - TS2564 - Property 'a' has no initializer and is not definitely assigned in the constructor.
         a: string;
+        // @ts-expect-error [FEI-5011] - TS2564 - Property 'b' has no initializer and is not definitely assigned in the constructor.
         b: string;
     }
     const foo = new Foo();
diff --git a/packages/wonder-stuff-core/src/__tests__/values.test.js b/packages/wonder-stuff-core/src/__tests__/values.test.ts
similarity index 73%
rename from packages/wonder-stuff-core/src/__tests__/values.test.js
rename to packages/wonder-stuff-core/src/__tests__/values.test.ts
index e4eb524f..5647966f 100644
--- a/packages/wonder-stuff-core/src/__tests__/values.test.js
+++ b/packages/wonder-stuff-core/src/__tests__/values.test.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module '../values' or its corresponding type declarations.
 import {values} from "../values";
 
 describe("#values", () => {
@@ -9,7 +9,7 @@ describe("#values", () => {
             a: 1,
             b: "2",
             c: [3, 4],
-        };
+        } as const;
 
         // Act
         values(obj);
@@ -24,7 +24,8 @@ describe("#values", () => {
             a: 1,
             b: "2",
             c: [3, 4],
-        };
+        } as const;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'any[]'.
         jest.spyOn(Object, "values").mockReturnValue("THE RESULT");
 
         // Act
diff --git a/packages/wonder-stuff-core/src/build-caused-by-message.js b/packages/wonder-stuff-core/src/build-caused-by-message.ts
similarity index 83%
rename from packages/wonder-stuff-core/src/build-caused-by-message.js
rename to packages/wonder-stuff-core/src/build-caused-by-message.ts
index 06f4a643..a8922236 100644
--- a/packages/wonder-stuff-core/src/build-caused-by-message.js
+++ b/packages/wonder-stuff-core/src/build-caused-by-message.ts
@@ -1,4 +1,3 @@
-// @flow
 /**
  * Builds a string that describes the causal relationship between two messages.
  *
@@ -8,10 +7,10 @@
  * @returns {string} A string that indicates `consequence` is caused by `cause`.
  */
 export const buildCausedByMessage = (
-    consequence: ?string,
-    cause: ?string,
+    consequence?: string | null,
+    cause?: string | null,
 ): string => {
-    const messageOrDefault = (message: ?string): string =>
+    const messageOrDefault = (message?: string | null): string =>
         message?.trim() || "(empty message)";
 
     const consequenceMessage = messageOrDefault(consequence);
diff --git a/packages/wonder-stuff-core/src/clone-metadata.js b/packages/wonder-stuff-core/src/clone-metadata.ts
similarity index 78%
rename from packages/wonder-stuff-core/src/clone-metadata.js
rename to packages/wonder-stuff-core/src/clone-metadata.ts
index 37315cc4..5fbfae66 100644
--- a/packages/wonder-stuff-core/src/clone-metadata.js
+++ b/packages/wonder-stuff-core/src/clone-metadata.ts
@@ -1,4 +1,3 @@
-// @flow
 import {clone} from "./clone";
 import type {Metadata} from "./types";
 
@@ -8,9 +7,9 @@ import type {Metadata} from "./types";
  * This performs a deep clone of the given metadata and returns a read-only
  * clone.
  */
-export const cloneMetadata = <T: Metadata>(
-    metadata: ?$ReadOnly<T>,
-): ?$ReadOnly<T> => {
+export const cloneMetadata = <T extends Metadata>(
+    metadata?: Readonly<T> | null,
+): Readonly<T> | null | undefined => {
     // If it's null or undefined, just return it as-is.
     if (metadata == null) {
         return metadata;
@@ -21,6 +20,5 @@ export const cloneMetadata = <T: Metadata>(
 
     // We know that we have cloned the incoming data and so our clone is of
     // the correct type.
-    // $FlowIgnore[incompatible-return]
     return Object.freeze(clonedValue);
 };
diff --git a/packages/wonder-stuff-core/src/clone.js b/packages/wonder-stuff-core/src/clone.ts
similarity index 69%
rename from packages/wonder-stuff-core/src/clone.js
rename to packages/wonder-stuff-core/src/clone.ts
index 41a6b469..57bebd74 100644
--- a/packages/wonder-stuff-core/src/clone.js
+++ b/packages/wonder-stuff-core/src/clone.ts
@@ -1,5 +1,3 @@
-// @flow
-
 /**
  * Clone a value and all of its nested values.
  *
@@ -14,14 +12,15 @@ export const clone = <T>(value: T): T => {
     }
 
     if (Array.isArray(value)) {
+        // @ts-expect-error [FEI-5011] - TS2322 - Type 'any[]' is not assignable to type 'T'.
         return value.map(clone);
     }
 
     return Object.keys(value).reduce((acc, key) => {
+        // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'unknown'.
         acc[key] = clone(value[key]);
         return acc;
         // We need to cast to any here so that the value is a valid
         // match for T in the return type after the accumulator is done.
-        // $FlowIgnore[unclear-type]
-    }, ({}: any));
+    }, {} as any);
 };
diff --git a/packages/wonder-stuff-core/src/entries.js b/packages/wonder-stuff-core/src/entries.js
deleted file mode 100644
index f6f05a7c..00000000
--- a/packages/wonder-stuff-core/src/entries.js
+++ /dev/null
@@ -1,16 +0,0 @@
-// @flow
-/**
- * Return an array of key/value tuples for an object.
- *
- * @param {$ReadOnly<interface {[K]: V}>} obj The object for which the values are
- * to be returned.
- * @returns {Array<[K, V]>} An array of key/value tuples for the object.
- */
-export function entries<K, V>(
-    obj: $ReadOnly<interface {[K]: V}>,
-): Array<[K, V]> {
-    // This cast is deliberate as Object.entries is typed to return
-    // Array<[string, mixed]>, but we want to return Array<[K, V]>.
-    // $FlowIgnore[unclear-type]
-    return (Object.entries(obj): any);
-}
diff --git a/packages/wonder-stuff-core/src/error-info.js b/packages/wonder-stuff-core/src/error-info.ts
similarity index 97%
rename from packages/wonder-stuff-core/src/error-info.js
rename to packages/wonder-stuff-core/src/error-info.ts
index b88c38b4..8ffdccda 100644
--- a/packages/wonder-stuff-core/src/error-info.js
+++ b/packages/wonder-stuff-core/src/error-info.ts
@@ -1,4 +1,3 @@
-// @flow
 import {buildCausedByMessage} from "./build-caused-by-message";
 
 /**
@@ -8,14 +7,14 @@ import {buildCausedByMessage} from "./build-caused-by-message";
  * information.
  */
 export class ErrorInfo {
-    +_name: string;
-    +_message: string;
-    +_stackFrames: $ReadOnlyArray<string>;
+    readonly _name: string;
+    readonly _message: string;
+    readonly _stackFrames: ReadonlyArray<string>;
 
     constructor(
         name: string,
         message: string,
-        stackFrames: $ReadOnlyArray<string>,
+        stackFrames: ReadonlyArray<string>,
     ) {
         this._name = name;
         this._message = message;
@@ -50,7 +49,7 @@ export class ErrorInfo {
      *
      * Index 0 being the top of the stack.
      */
-    get stack(): $ReadOnlyArray<string> {
+    get stack(): ReadonlyArray<string> {
         // Copy the stack array just to be sure our internal state won't
         // mutate outside our control.
         return [...this._stackFrames];
diff --git a/packages/wonder-stuff-core/src/errors-from-error.js b/packages/wonder-stuff-core/src/errors-from-error.ts
similarity index 82%
rename from packages/wonder-stuff-core/src/errors-from-error.js
rename to packages/wonder-stuff-core/src/errors-from-error.ts
index ace72464..174f3a46 100644
--- a/packages/wonder-stuff-core/src/errors-from-error.js
+++ b/packages/wonder-stuff-core/src/errors-from-error.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError} from "./kind-error";
 import {Errors} from "./errors";
 
@@ -7,7 +6,7 @@ export const Order = Object.freeze({
     CauseFirst: "cause-first",
 });
 
-export type SequenceOrder = $Values<typeof Order>;
+export type SequenceOrder = (typeof Order)[keyof typeof Order];
 
 /**
  * Given an error, generates a sequence of `Error`s.
@@ -20,7 +19,7 @@ export type SequenceOrder = $Values<typeof Order>;
  * causal error and ends with the given error.
  */
 export function* errorsFromError(
-    error: ?Error,
+    error: Error | null | undefined,
     order: SequenceOrder,
 ): Iterator<Error> {
     if (order !== Order.CauseFirst && order !== Order.ConsequenceFirst) {
@@ -38,6 +37,7 @@ export function* errorsFromError(
         yield error;
     }
     if (error instanceof KindError) {
+        // @ts-expect-error [FEI-5011] - TS2488 - Type 'Iterator<Error, any, undefined>' must have a '[Symbol.iterator]()' method that returns an iterator.
         yield* errorsFromError(error.cause, order);
     }
     if (order === Order.CauseFirst) {
diff --git a/packages/wonder-stuff-core/src/errors.js b/packages/wonder-stuff-core/src/errors.ts
similarity index 98%
rename from packages/wonder-stuff-core/src/errors.js
rename to packages/wonder-stuff-core/src/errors.ts
index 984ef615..fae0ac0f 100644
--- a/packages/wonder-stuff-core/src/errors.js
+++ b/packages/wonder-stuff-core/src/errors.ts
@@ -1,5 +1,3 @@
-// @flow
-
 /**
  * @typedef {Object} Errors A base error taxonomy for consumers of this core
  * library to build off.
diff --git a/packages/wonder-stuff-core/src/get-kind-from-error.js b/packages/wonder-stuff-core/src/get-kind-from-error.ts
similarity index 96%
rename from packages/wonder-stuff-core/src/get-kind-from-error.js
rename to packages/wonder-stuff-core/src/get-kind-from-error.ts
index a74966f7..ad2c47c1 100644
--- a/packages/wonder-stuff-core/src/get-kind-from-error.js
+++ b/packages/wonder-stuff-core/src/get-kind-from-error.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError} from "./kind-error";
 import {Errors} from "./errors";
 
diff --git a/packages/wonder-stuff-core/src/get-original-stack-from-error.js b/packages/wonder-stuff-core/src/get-original-stack-from-error.ts
similarity index 72%
rename from packages/wonder-stuff-core/src/get-original-stack-from-error.js
rename to packages/wonder-stuff-core/src/get-original-stack-from-error.ts
index 893f82f1..3b263660 100644
--- a/packages/wonder-stuff-core/src/get-original-stack-from-error.js
+++ b/packages/wonder-stuff-core/src/get-original-stack-from-error.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError} from "./kind-error";
 
 /**
@@ -8,5 +7,6 @@ export const getOriginalStackFromError = (error: Error): string => {
     if (error instanceof KindError) {
         return error.originalStack;
     }
+    // @ts-expect-error [FEI-5011] - TS2322 - Type 'string | undefined' is not assignable to type 'string'.
     return error.stack;
 };
diff --git a/packages/wonder-stuff-core/src/index.js b/packages/wonder-stuff-core/src/index.ts
similarity index 61%
rename from packages/wonder-stuff-core/src/index.js
rename to packages/wonder-stuff-core/src/index.ts
index 15431d91..99da6593 100644
--- a/packages/wonder-stuff-core/src/index.js
+++ b/packages/wonder-stuff-core/src/index.ts
@@ -1,7 +1,9 @@
-// @flow
 export {clone} from "./clone";
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module './entries' or its corresponding type declarations.
 export {entries} from "./entries";
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module './keys' or its corresponding type declarations.
 export {keys} from "./keys";
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module './values' or its corresponding type declarations.
 export {values} from "./values";
 export {Errors} from "./errors";
 export {errorsFromError, Order} from "./errors-from-error";
diff --git a/packages/wonder-stuff-core/src/keys.js b/packages/wonder-stuff-core/src/keys.js
deleted file mode 100644
index 19a18423..00000000
--- a/packages/wonder-stuff-core/src/keys.js
+++ /dev/null
@@ -1,13 +0,0 @@
-// @flow
-/**
- * Return an array of the enumerable keys of an object.
- *
- * @param {$ReadOnly<interface {[string]: mixed}>} obj The object for which the values are
- * to be returned.
- * @returns {Array<$Keys<O>>} An array of the enumerable keys of an object.
- */
-export function keys<O: interface {[string]: mixed}>(
-    obj: $ReadOnly<O>,
-): Array<$Keys<O>> {
-    return Object.keys(obj);
-}
diff --git a/packages/wonder-stuff-core/src/kind-error.js b/packages/wonder-stuff-core/src/kind-error.ts
similarity index 88%
rename from packages/wonder-stuff-core/src/kind-error.js
rename to packages/wonder-stuff-core/src/kind-error.ts
index be7b0396..bb893f3f 100644
--- a/packages/wonder-stuff-core/src/kind-error.js
+++ b/packages/wonder-stuff-core/src/kind-error.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors} from "./errors";
 import {ErrorInfo} from "./error-info";
 import {cloneMetadata} from "./clone-metadata";
@@ -8,56 +7,50 @@ import type {Metadata} from "./types";
 /**
  * Options for constructing a `KindError`.
  */
-export type Options = {|
+export type Options = {
     /**
      * An error responsible for the error being created.
      *
      * @type {?Error}
      */
-    cause?: ?Error,
-
+    cause?: Error | null | undefined;
     /**
      * Data to be attached to the error.
      *
      * @type {?Metadata}
      */
-    metadata?: ?Metadata,
-
+    metadata?: Metadata | null | undefined;
     /**
      * A prefix for the error name.
      *
      * @type {?string}
      */
-    prefix?: ?string,
-
+    prefix?: string | null | undefined;
     /**
      * A name for the error.
      *
      * @type {?string}
      */
-    name?: ?string,
-
+    name?: string | null | undefined;
     /**
      * The number of stack frames to strip from the error.
      *
      * @type {?number}
      */
-    stripStackFrames?: ?number,
-
+    stripStackFrames?: number | null | undefined;
     /**
      * The minimum number of stack frames to try and retain.
      *
      * @type {?number}
      */
-    minimumFrameCount?: ?number,
-
+    minimumFrameCount?: number | null | undefined;
     /**
      * Should we create a composite stack from the causal error chain or not?
      *
      * @type {?boolean}
      */
-    compositeStack?: ?boolean,
-|};
+    compositeStack?: boolean | null | undefined;
+};
 
 /**
  * An error to describe detailed states and relationships.
@@ -68,11 +61,11 @@ export type Options = {|
  * logging setups like Sentry or winston.
  */
 export class KindError extends Error {
-    +kind: string;
-    +originalMessage: string;
-    +originalStack: string;
-    +metadata: ?$ReadOnly<Metadata>;
-    +cause: ?Error;
+    readonly kind: string;
+    readonly originalMessage: string;
+    readonly originalStack: string;
+    readonly metadata: Readonly<Metadata> | null | undefined;
+    readonly cause: Error | null | undefined;
 
     /**
      * Creates an instance of `KindError`.
@@ -152,6 +145,7 @@ export class KindError extends Error {
         this.kind = kind;
 
         // Capture the original stack trace, in case we change it.
+        // @ts-expect-error [FEI-5011] - TS2322 - Type 'string | undefined' is not assignable to type 'string'.
         this.originalStack = this.stack;
 
         // The cause of this error, if there is one.
@@ -165,16 +159,6 @@ export class KindError extends Error {
             minimumFrameCount ?? 1,
         );
 
-        /**
-         * $FlowIgnore[incompatible-type]
-         * Flow doesn't like us leaving KAError temporarily without a
-         * stack, but I don't want this crashing because we try to
-         * assign to a readonly thing, so being mildly cautious.
-         *
-         * We're going to replace the stack with our normalized one or
-         * one combined with our cause - so we need to make sure the old one is
-         * gone.
-         */
         delete this.stack;
 
         // The default is the normalized stack.
diff --git a/packages/wonder-stuff-core/src/safe-stringify.js b/packages/wonder-stuff-core/src/safe-stringify.ts
similarity index 96%
rename from packages/wonder-stuff-core/src/safe-stringify.js
rename to packages/wonder-stuff-core/src/safe-stringify.ts
index dde437ef..5468b8e3 100644
--- a/packages/wonder-stuff-core/src/safe-stringify.js
+++ b/packages/wonder-stuff-core/src/safe-stringify.ts
@@ -1,5 +1,3 @@
-// @flow
-
 /**
  * Options to modify how a safe stringifying operation works.
  */
@@ -10,8 +8,7 @@ type SafeStringifyOptions = {
      * @default '""' Empty string
      * @type {string}
      */
-    defaultValue?: string,
-
+    defaultValue?: string;
     /**
      * A number indicating how many spaces to indent nested structures.
      * When not given, there will be no indentation nor additional newlines.
@@ -19,7 +16,7 @@ type SafeStringifyOptions = {
      * @default undefined No indentation
      * @type {?number}
      */
-    indent?: ?number,
+    indent?: number | null | undefined;
 };
 
 interface safeStringifyFn {
@@ -37,7 +34,6 @@ interface safeStringifyFn {
      * @returns {string} The stringified value or the default value.
      */
     <T>(value: T, options?: SafeStringifyOptions): string;
-
     /**
      * Stringify an item, returning an empty string on error, null, or undefined.
      *
@@ -76,7 +72,7 @@ export const safeStringify: safeStringifyFn = <T>(
     }
     try {
         return JSON.stringify(value, null, indent ?? 0) ?? defaultValue;
-    } catch (_) {
+    } catch (_: any) {
         return defaultValue;
     }
 };
diff --git a/packages/wonder-stuff-core/src/truncate-middle.js b/packages/wonder-stuff-core/src/truncate-middle.ts
similarity index 99%
rename from packages/wonder-stuff-core/src/truncate-middle.js
rename to packages/wonder-stuff-core/src/truncate-middle.ts
index d6595341..29036334 100644
--- a/packages/wonder-stuff-core/src/truncate-middle.js
+++ b/packages/wonder-stuff-core/src/truncate-middle.ts
@@ -1,4 +1,3 @@
-// @flow
 const ELLIPSIS = "...";
 
 /**
diff --git a/packages/wonder-stuff-core/src/types.js b/packages/wonder-stuff-core/src/types.ts
similarity index 58%
rename from packages/wonder-stuff-core/src/types.js
rename to packages/wonder-stuff-core/src/types.ts
index 04e66f0c..926a073a 100644
--- a/packages/wonder-stuff-core/src/types.js
+++ b/packages/wonder-stuff-core/src/types.ts
@@ -1,5 +1,4 @@
-// @flow
-type MetadataPrimitive = string | number | boolean | null | void;
+type MetadataPrimitive = string | number | boolean | null | undefined;
 type MetadataArray<T> = Array<T | MetadataArray<T>>;
 
 /**
@@ -9,5 +8,5 @@ export type Metadata = {
     [name: string]:
         | Metadata
         | MetadataPrimitive
-        | MetadataArray<MetadataPrimitive | Metadata>,
+        | MetadataArray<MetadataPrimitive | Metadata>;
 };
diff --git a/packages/wonder-stuff-core/src/values.js b/packages/wonder-stuff-core/src/values.js
deleted file mode 100644
index 73401dad..00000000
--- a/packages/wonder-stuff-core/src/values.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// @flow
-/**
- * Return an array of the enumerable property values of an object.
- *
- * @param {$ReadOnly<interface {[mixed]: V}>} obj The object for which the values are
- * to be returned.
- * @returns {Array<V>} An array of the enumerable property values of the object.
- */
-export function values<V>(obj: $ReadOnly<interface {[mixed]: V}>): Array<V> {
-    // This is a deliberate cast through any.
-    // Object.values returns Array<mixed> and we want to return Array<V>.
-    // $FlowIgnore[unclear-type]
-    return (Object.values(obj): Array<any>);
-}
diff --git a/packages/wonder-stuff-i18n/src/bin/all-i18n-strings.js b/packages/wonder-stuff-i18n/src/bin/all-i18n-strings.ts
old mode 100755
new mode 100644
similarity index 98%
rename from packages/wonder-stuff-i18n/src/bin/all-i18n-strings.js
rename to packages/wonder-stuff-i18n/src/bin/all-i18n-strings.ts
index 6c01b269..d8536b92
--- a/packages/wonder-stuff-i18n/src/bin/all-i18n-strings.js
+++ b/packages/wonder-stuff-i18n/src/bin/all-i18n-strings.ts
@@ -1,5 +1,4 @@
 #!/usr/bin/env node
-// @flow
 /* istanbul ignore file */
 /* eslint-disable no-console */
 /**
diff --git a/packages/wonder-stuff-i18n/src/bin/gen-potfile.js b/packages/wonder-stuff-i18n/src/bin/gen-potfile.ts
old mode 100755
new mode 100644
similarity index 99%
rename from packages/wonder-stuff-i18n/src/bin/gen-potfile.js
rename to packages/wonder-stuff-i18n/src/bin/gen-potfile.ts
index ea23d98f..7a6aa561
--- a/packages/wonder-stuff-i18n/src/bin/gen-potfile.js
+++ b/packages/wonder-stuff-i18n/src/bin/gen-potfile.ts
@@ -1,5 +1,4 @@
 #!/usr/bin/env node
-// @flow
 /* istanbul ignore file */
 /**
  * Generates a POT file containing all strings marked for translation. The POT
diff --git a/packages/wonder-stuff-i18n/src/index.js b/packages/wonder-stuff-i18n/src/index.ts
similarity index 98%
rename from packages/wonder-stuff-i18n/src/index.js
rename to packages/wonder-stuff-i18n/src/index.ts
index 6eb09840..4657ca52 100644
--- a/packages/wonder-stuff-i18n/src/index.js
+++ b/packages/wonder-stuff-i18n/src/index.ts
@@ -1,4 +1,3 @@
-// @flow
 /* istanbul ignore file */
 export {default as I18nPlugin} from "./plugins/i18n-plugin";
 export {extractStrings} from "./utils/extract-i18n";
diff --git a/packages/wonder-stuff-i18n/src/plugins/__tests__/i18n-plugin.test.js b/packages/wonder-stuff-i18n/src/plugins/__tests__/i18n-plugin.test.ts
similarity index 90%
rename from packages/wonder-stuff-i18n/src/plugins/__tests__/i18n-plugin.test.js
rename to packages/wonder-stuff-i18n/src/plugins/__tests__/i18n-plugin.test.ts
index 27dc7d04..cdb02d26 100644
--- a/packages/wonder-stuff-i18n/src/plugins/__tests__/i18n-plugin.test.js
+++ b/packages/wonder-stuff-i18n/src/plugins/__tests__/i18n-plugin.test.ts
@@ -1,17 +1,16 @@
-// @flow
 import I18nPlugin from "../i18n-plugin";
 
 import type {TranslatedLocaleStrings} from "../../utils/i18n-utils";
 import type {TranslatedStrings, Assets} from "../i18n-plugin";
 
-type ResolvedAssets = {|
-    [string]: ResolvedAsset,
-|};
+type ResolvedAssets = {
+    [key: string]: ResolvedAsset;
+};
 
-type ResolvedAsset = {|
-    source: string,
-    size: number,
-|};
+type ResolvedAsset = {
+    source: string;
+    size: number;
+};
 
 describe("I18nPlugin", () => {
     describe("constructor", () => {
@@ -22,7 +21,7 @@ describe("I18nPlugin", () => {
 
             // Assert
             expect(() => {
-                // $FlowIgnore
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 new I18nPlugin(); // eslint-disable-line no-new
             }).toThrowErrorMatchingInlineSnapshot(
                 `"I18nPlugin requires options"`,
@@ -36,7 +35,7 @@ describe("I18nPlugin", () => {
 
             // Assert
             expect(() => {
-                // $FlowIgnore
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{}' is not assignable to parameter of type 'Options'.
                 new I18nPlugin({}); // eslint-disable-line no-new
             }).toThrowErrorMatchingInlineSnapshot(
                 `"Must provide locales to localize to"`,
@@ -50,7 +49,7 @@ describe("I18nPlugin", () => {
 
             // Assert
             expect(() => {
-                // $FlowIgnore
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ locales: never[]; }' is not assignable to parameter of type 'Options'.
                 new I18nPlugin({locales: []}); // eslint-disable-line no-new
             }).toThrowErrorMatchingInlineSnapshot(
                 `"Must provide a function to get the strings to localize"`,
@@ -174,7 +173,7 @@ describe("I18nPlugin", () => {
                         return 1;
                     },
                 },
-            };
+            } as const;
             const locales = ["es", "pt"];
             const plugin = new I18nPlugin({
                 locales,
@@ -208,7 +207,9 @@ describe("I18nPlugin", () => {
             const stringAssets: ResolvedAssets = {};
             for (const assetName of Object.keys(assets)) {
                 stringAssets[assetName] = {
+                    // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly "test.deadbeefc0ffeec0ffee.js": { readonly source: () => string; readonly size: () => number; }; readonly "test-pluralonly.deadbeefc0ffeec0ffe2.js": { readonly source: () => string; readonly size: () => number; }; }'.
                     source: assets[assetName].source(),
+                    // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly "test.deadbeefc0ffeec0ffee.js": { readonly source: () => string; readonly size: () => number; }; readonly "test-pluralonly.deadbeefc0ffeec0ffe2.js": { readonly source: () => string; readonly size: () => number; }; }'.
                     size: assets[assetName].size(),
                 };
             }
@@ -296,7 +297,7 @@ describe("I18nPlugin", () => {
                         return 1;
                     },
                 },
-            };
+            } as const;
             const locales = ["es", "pt"];
             const plugin = new I18nPlugin({
                 locales,
@@ -317,7 +318,9 @@ describe("I18nPlugin", () => {
             const stringAssets: ResolvedAssets = {};
             for (const assetName of Object.keys(assets)) {
                 stringAssets[assetName] = {
+                    // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly "test.css": { readonly source: () => string; readonly size: () => number; }; readonly "font.woff2": { readonly source: () => string; readonly size: () => number; }; }'.
                     source: assets[assetName].source(),
+                    // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly "test.css": { readonly source: () => string; readonly size: () => number; }; readonly "font.woff2": { readonly source: () => string; readonly size: () => number; }; }'.
                     size: assets[assetName].size(),
                 };
             }
@@ -401,7 +404,7 @@ describe("I18nPlugin", () => {
                 locales,
                 silent: true,
                 getI18nStrings: jest.fn().mockResolvedValue({}),
-                shouldLocalizeAsset: (assetName) =>
+                shouldLocalizeAsset: (assetName: any) =>
                     assetName.startsWith("runtime.") ||
                     assetName.startsWith("chunk-map."),
             });
@@ -591,7 +594,7 @@ describe("I18nPlugin", () => {
                     deadbeefc0ffeec0ffe2: "efba0b9130c816f63328",
                     deadbeefc0ffeec0ffee: "68b8d9a0a2ba472e983b",
                 },
-            };
+            } as const;
             const assets = {
                 "test.deadbeefc0ffeec0ffee.js": {
                     source() {
@@ -665,7 +668,7 @@ describe("I18nPlugin", () => {
                         return 1;
                     },
                 },
-            };
+            } as const;
             const getLocalePath = (locale: string) => `/prod/${locale}`;
             const locales = ["es", "pt"];
             const plugin = new I18nPlugin({
@@ -673,7 +676,7 @@ describe("I18nPlugin", () => {
                 silent: true,
                 getI18nStrings: jest.fn().mockResolvedValue({}),
                 getLocalePath,
-                shouldLocalizeManifest: (assetName, locale) =>
+                shouldLocalizeManifest: (assetName: any, locale: any) =>
                     assetName.includes(`/${locale}/`),
             });
 
@@ -686,7 +689,9 @@ describe("I18nPlugin", () => {
             const stringAssets: ResolvedAssets = {};
             for (const assetName of Object.keys(assets)) {
                 stringAssets[assetName] = {
+                    // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly "test.deadbeefc0ffeec0ffee.js": { readonly source: () => string; readonly size: () => number; }; readonly "runtime.deadbeefc0ffeec0ffe2.js": { readonly source: () => string; readonly size: () => number; }; ... 6 more ...; readonly "../pages/pt/page-1234.html": { ...; }; }'.
                     source: assets[assetName].source(),
+                    // @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly "test.deadbeefc0ffeec0ffee.js": { readonly source: () => string; readonly size: () => number; }; readonly "runtime.deadbeefc0ffeec0ffe2.js": { readonly source: () => string; readonly size: () => number; }; ... 6 more ...; readonly "../pages/pt/page-1234.html": { ...; }; }'.
                     size: assets[assetName].size(),
                 };
             }
@@ -748,7 +753,7 @@ describe("I18nPlugin", () => {
                     deadbeefc0ffeec0ffe2: "efba0b9130c816f63328",
                     deadbeefc0ffeec0ffee: "68b8d9a0a2ba472e983b",
                 },
-            };
+            } as const;
             const assets: Assets = {
                 "../manifests/es/webpack-manifest-1234.json": {
                     source() {
@@ -815,7 +820,7 @@ describe("I18nPlugin", () => {
                     deadbeefc0ffeec0ffe2: "efba0b9130c816f63328",
                     deadbeefc0ffeec0ffee: "68b8d9a0a2ba472e983b",
                 },
-            };
+            } as const;
             const assets: Assets = {
                 "../manifests/es/webpack-manifest-1234.json": {
                     source() {
@@ -876,22 +881,19 @@ describe("I18nPlugin", () => {
     describe("onEmit", () => {
         it("processes all the necessary steps", async () => {
             // Arrange
-            const assets = {};
-            const translatedStrings = {translatedStrings: true};
-            const hashMap = {hashMap: true};
+            const assets: Record<string, any> = {};
+            const translatedStrings = {translatedStrings: true} as const;
+            const hashMap = {hashMap: true} as const;
             const locales = ["es", "pt"];
             const plugin = new I18nPlugin({
                 locales,
                 silent: true,
                 getI18nStrings: jest.fn().mockResolvedValue({}),
             });
-            // $FlowIgnore This is a mock.
             plugin.getTranslatedStrings = jest
                 .fn()
                 .mockReturnValue(translatedStrings);
-            // $FlowIgnore This is a mock.
             plugin.translateAssets = jest.fn().mockReturnValue(hashMap);
-            // $FlowIgnore This is a mock.
             plugin.localizeManifests = jest.fn();
             const callback = jest.fn();
 
@@ -899,22 +901,18 @@ describe("I18nPlugin", () => {
             await plugin.onEmit({assets}, callback);
 
             // Assert
-            // $FlowIgnore This is a mock.
             expect(plugin.getTranslatedStrings).toHaveBeenCalledWith(locales);
-            // $FlowIgnore This is a mock.
             expect(plugin.translateAssets).toHaveBeenCalledWith({
                 assets,
                 translatedStrings,
                 localizeRuntimeFiles: false,
             });
-            // $FlowIgnore This is a mock.
             expect(plugin.translateAssets).toHaveBeenCalledWith({
                 assets,
                 translatedStrings,
                 hashMap,
                 localizeRuntimeFiles: true,
             });
-            // $FlowIgnore This is a mock.
             expect(plugin.localizeManifests).toHaveBeenCalledWith({
                 assets,
                 hashMap,
@@ -924,22 +922,19 @@ describe("I18nPlugin", () => {
 
         it("skips all the steps when there are no valid locales", async () => {
             // Arrange
-            const assets = {};
-            const translatedStrings = {translatedStrings: true};
-            const hashMap = {hashMap: true};
-            const locales = [];
+            const assets: Record<string, any> = {};
+            const translatedStrings = {translatedStrings: true} as const;
+            const hashMap = {hashMap: true} as const;
+            const locales: Array<any> = [];
             const plugin = new I18nPlugin({
                 locales,
                 silent: true,
                 getI18nStrings: jest.fn().mockResolvedValue({}),
             });
-            // $FlowIgnore This is a mock.
             plugin.getTranslatedStrings = jest
                 .fn()
                 .mockReturnValue(translatedStrings);
-            // $FlowIgnore This is a mock.
             plugin.translateAssets = jest.fn().mockReturnValue(hashMap);
-            // $FlowIgnore This is a mock.
             plugin.localizeManifests = jest.fn();
             const callback = jest.fn();
 
@@ -947,11 +942,8 @@ describe("I18nPlugin", () => {
             await plugin.onEmit({assets}, callback);
 
             // Assert
-            // $FlowIgnore This is a mock.
             expect(plugin.getTranslatedStrings).not.toHaveBeenCalled();
-            // $FlowIgnore This is a mock.
             expect(plugin.translateAssets).not.toHaveBeenCalled();
-            // $FlowIgnore This is a mock.
             expect(plugin.localizeManifests).not.toHaveBeenCalled();
             expect(callback).toHaveBeenCalled();
         });
diff --git a/packages/wonder-stuff-i18n/src/plugins/i18n-plugin.js b/packages/wonder-stuff-i18n/src/plugins/i18n-plugin.ts
similarity index 88%
rename from packages/wonder-stuff-i18n/src/plugins/i18n-plugin.js
rename to packages/wonder-stuff-i18n/src/plugins/i18n-plugin.ts
index e45905be..ac5977d2 100644
--- a/packages/wonder-stuff-i18n/src/plugins/i18n-plugin.js
+++ b/packages/wonder-stuff-i18n/src/plugins/i18n-plugin.ts
@@ -1,4 +1,3 @@
-// @flow
 /**
  * A plugin to create translated versions of Webpack builds. After Webpack compiles
  * all the JS bundles, this plugin goes through all the generated assets and
@@ -18,6 +17,7 @@
  *
  */
 import path from "path";
+// @ts-expect-error [FEI-5011] - TS7016 - Could not find a declaration file for module 'async'. '/Users/kevinbarabash/khan/wonder-stuff/node_modules/async/dist/async.js' implicitly has an 'any' type.
 import {eachLimit} from "async";
 
 import * as I18nUtils from "../utils/i18n-utils";
@@ -49,7 +49,7 @@ const addAsset = (assets: Assets, relFilePath: string, data: string) => {
 };
 
 export type TranslatedStrings = {
-    [locale: string]: TranslatedLocaleStrings,
+    [locale: string]: TranslatedLocaleStrings;
 };
 
 type Options = {
@@ -57,8 +57,7 @@ type Options = {
      * The locales to build. Should be a list of strings like "pt", "es", etc.
      * Be sure to not include "en" in this list, as that is the default locale.
      */
-    locales: Array<string>,
-
+    locales: Array<string>;
     /**
      * Get localized strings for a particular locale.
      *
@@ -77,75 +76,71 @@ type Options = {
      *     ...
      * }
      */
-    getI18nStrings: (locale: string) => Promise<TranslatedLocaleStrings>,
-
+    getI18nStrings: (locale: string) => Promise<TranslatedLocaleStrings>;
     /**
      * Provide a partial path to the Webpack output directory that includes
      * the locale. Defaults to: "/<locale>/".
      */
-    getLocalePath?: (locale: string) => string,
-
+    getLocalePath?: (locale: string) => string;
     /**
      * Indicate if an asset should have the hashes and URLs inside of it
      * updated to use the new locale. Defaults to handling any bundle named
      * "runtime" (you will want to do this for any bundle that contains
      * the runtime or has references to other JS files)
      */
-    shouldLocalizeAsset?: (assetName: string) => boolean,
-
+    shouldLocalizeAsset?: (assetName: string) => boolean;
     /**
      * Determine if a file should be processed, meaning if it should be copied
      * over to the new locale directory. Defaults to all files.
      */
-    shouldProcessAsset?: (assetName: string) => boolean,
-
+    shouldProcessAsset?: (assetName: string) => boolean;
     /**
      * Determine if a manifest file, for a given locale should be modified to
      * point to the new JS files or assets. Defaults to processing all '.html'
      * files.
      */
-    shouldLocalizeManifest?: (assetName: string, locale: string) => boolean,
-
+    shouldLocalizeManifest?: (assetName: string, locale: string) => boolean;
     /**
      * Should the plugin log any messages to the console? Defaults to true.
      */
-    silent?: boolean,
-
+    silent?: boolean;
     /**
      * Should the plugin log any timing information? None is logged by default.
      */
     timing?: {
-        start: (string) => void,
-        end: (string) => void,
-        ...
-    },
+        start: (arg1: string) => void;
+        end: (arg1: string) => void;
+    };
 };
 
 type InternalOptions = {
-    locales: Array<string>,
-    silent?: boolean,
+    locales: Array<string>;
+    silent?: boolean;
     timing?: {
-        start: (string) => void,
-        end: (string) => void,
-        ...
-    },
-    getI18nStrings: (locale: string) => Promise<TranslatedLocaleStrings>,
-    getLocalePath: (locale: string) => string,
-    shouldLocalizeAsset: (assetName: string) => boolean,
-    shouldProcessAsset: (assetName: string) => boolean,
-    shouldLocalizeManifest: (assetName: string, locale: string) => boolean,
+        start: (arg1: string) => void;
+        end: (arg1: string) => void;
+    };
+    getI18nStrings: (locale: string) => Promise<TranslatedLocaleStrings>;
+    getLocalePath: (locale: string) => string;
+    shouldLocalizeAsset: (assetName: string) => boolean;
+    shouldProcessAsset: (assetName: string) => boolean;
+    shouldLocalizeManifest: (assetName: string, locale: string) => boolean;
 };
 
-type LocaleHashMap = {[oldHash: string]: string};
-type HashMaps = {[locale: string]: LocaleHashMap};
+type LocaleHashMap = {
+    [oldHash: string]: string;
+};
+type HashMaps = {
+    [locale: string]: LocaleHashMap;
+};
 
-type Asset = {|
-    source: () => string,
-    size: () => number,
-|};
+type Asset = {
+    source: () => string;
+    size: () => number;
+};
 
 export type Assets = {
-    [assetName: string]: Asset,
+    [assetName: string]: Asset;
 };
 
 export default class I18nPlugin {
@@ -183,7 +178,8 @@ export default class I18nPlugin {
     }
 
     /* istanbul ignore next */
-    apply(compiler: $FlowFixMe) {
+    apply(compiler: any) {
+        // @ts-expect-error [FEI-5011] - TS7006 - Parameter 'options' implicitly has an 'any' type. | TS7006 - Parameter 'callback' implicitly has an 'any' type.
         compiler.hooks.emit.tapAsync("I18nPlugin", (options, callback) =>
             this.onEmit(options, callback),
         );
@@ -194,7 +190,7 @@ export default class I18nPlugin {
      *
      * @param  {...any} args the args to log out to the console
      */
-    log(...args: Array<$FlowFixMe>) {
+    log(...args: Array<any>) {
         const {silent} = this.options;
         if (silent === false || silent == null) {
             // eslint-disable-next-line no-console
@@ -223,6 +219,7 @@ export default class I18nPlugin {
         }
 
         // Download the strings for each locale in parallel
+        // @ts-expect-error [FEI-5011] - TS7006 - Parameter 'locale' implicitly has an 'any' type.
         await eachLimit(locales, 4, async (locale) => {
             this.log(
                 `Retreiving strings for ${locale} ${getEmojiForLocale(locale)}`,
@@ -251,10 +248,10 @@ export default class I18nPlugin {
         localizeRuntimeFiles,
         hashMap,
     }: {
-        assets: Assets,
-        translatedStrings: TranslatedStrings,
-        localizeRuntimeFiles: boolean,
-        hashMap?: HashMaps,
+        assets: Assets;
+        translatedStrings: TranslatedStrings;
+        localizeRuntimeFiles: boolean;
+        hashMap?: HashMaps;
     }): HashMaps {
         const {
             locales,
@@ -279,7 +276,7 @@ export default class I18nPlugin {
 
         // Initialize the map of old hashes to new hashes for each locale
         if (!hashMap) {
-            hashMap = ({}: HashMaps);
+            hashMap = {} as HashMaps;
 
             for (const locale of locales) {
                 hashMap[locale] = {};
@@ -380,7 +377,7 @@ export default class I18nPlugin {
      *
      * @param {assets: Object<string, Object>, hashMap: <string, string>} options
      */
-    localizeManifests({assets, hashMap}: {assets: Assets, hashMap: HashMaps}) {
+    localizeManifests({assets, hashMap}: {assets: Assets; hashMap: HashMaps}) {
         const {locales, timing, shouldLocalizeManifest, getLocalePath} =
             this.options;
 
@@ -427,7 +424,11 @@ export default class I18nPlugin {
      * @returns void
      */
     async onEmit(
-        {assets}: {assets: Assets},
+        {
+            assets,
+        }: {
+            assets: Assets;
+        },
         callback: () => void,
     ): Promise<void> {
         const {locales} = this.options;
diff --git a/packages/wonder-stuff-i18n/src/utils/__tests__/emoji-for-locale.test.js b/packages/wonder-stuff-i18n/src/utils/__tests__/emoji-for-locale.test.ts
similarity index 98%
rename from packages/wonder-stuff-i18n/src/utils/__tests__/emoji-for-locale.test.js
rename to packages/wonder-stuff-i18n/src/utils/__tests__/emoji-for-locale.test.ts
index 4f69c98b..c6dcc5c8 100644
--- a/packages/wonder-stuff-i18n/src/utils/__tests__/emoji-for-locale.test.js
+++ b/packages/wonder-stuff-i18n/src/utils/__tests__/emoji-for-locale.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {getEmojiForLocale} from "../emoji-for-locale";
 
 describe("getEmojiForLocale", () => {
diff --git a/packages/wonder-stuff-i18n/src/utils/__tests__/extract-i18n.test.js b/packages/wonder-stuff-i18n/src/utils/__tests__/extract-i18n.test.ts
similarity index 99%
rename from packages/wonder-stuff-i18n/src/utils/__tests__/extract-i18n.test.js
rename to packages/wonder-stuff-i18n/src/utils/__tests__/extract-i18n.test.ts
index 4bd98a82..dc5a13ca 100644
--- a/packages/wonder-stuff-i18n/src/utils/__tests__/extract-i18n.test.js
+++ b/packages/wonder-stuff-i18n/src/utils/__tests__/extract-i18n.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {extractStrings} from "../extract-i18n";
 
 const TEST_FILE = `
@@ -108,7 +107,7 @@ const zg = a(b("asdf"))._("Doesn't even use a variable.");
 describe("extractStrings", () => {
     it("extracts strings from a file", () => {
         // Arrange
-        const results = [];
+        const results: Array<any> = [];
 
         // Act
         for (const match of extractStrings(TEST_FILE)) {
@@ -397,7 +396,7 @@ describe("extractStrings", () => {
 
     it("extracted string exactly matches positions", () => {
         // Arrange
-        const results = [];
+        const results: Array<any> = [];
 
         // Act
         for (const match of extractStrings(TEST_FILE)) {
diff --git a/packages/wonder-stuff-i18n/src/utils/__tests__/i18n-utils.test.js b/packages/wonder-stuff-i18n/src/utils/__tests__/i18n-utils.test.ts
similarity index 97%
rename from packages/wonder-stuff-i18n/src/utils/__tests__/i18n-utils.test.js
rename to packages/wonder-stuff-i18n/src/utils/__tests__/i18n-utils.test.ts
index 7a67c3c5..d36a25e5 100644
--- a/packages/wonder-stuff-i18n/src/utils/__tests__/i18n-utils.test.js
+++ b/packages/wonder-stuff-i18n/src/utils/__tests__/i18n-utils.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import fs from "fs";
 
 import {
@@ -28,7 +27,7 @@ describe("getIgnoreGlobs", () => {
 
     it("returns nothing if no .i18nignore file is found", () => {
         // Arrange
-        const expectedGlobs = [];
+        const expectedGlobs: Array<any> = [];
         const ancesdir = require("ancesdir");
         ancesdir.mockImplementation(() => {
             throw new Error("No such file");
@@ -108,7 +107,7 @@ describe("translateString", () => {
         const translation = {
             Hello: "Hallo",
             World: "Welt",
-        };
+        } as const;
 
         // Act
         const translatedFileContents = translateString(
@@ -127,7 +126,7 @@ describe("translateString", () => {
         const fileContents = `i18n._("Hello");\ni18n._("World");`;
         const translation = {
             Hello: "Hallo",
-        };
+        } as const;
 
         // Act
         const translatedFileContents = translateString(
@@ -147,7 +146,7 @@ describe("translateString", () => {
         const translation = {
             Hello: "Hallo",
             World: "Welt",
-        };
+        } as const;
         const strings = getI18nStringsFromString(fileContents);
 
         // Act
diff --git a/packages/wonder-stuff-i18n/src/utils/__tests__/localize-file.test.js b/packages/wonder-stuff-i18n/src/utils/__tests__/localize-file.test.ts
similarity index 94%
rename from packages/wonder-stuff-i18n/src/utils/__tests__/localize-file.test.js
rename to packages/wonder-stuff-i18n/src/utils/__tests__/localize-file.test.ts
index e5c45793..a27e3088 100644
--- a/packages/wonder-stuff-i18n/src/utils/__tests__/localize-file.test.js
+++ b/packages/wonder-stuff-i18n/src/utils/__tests__/localize-file.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {
     extractHashFromFileName,
     localizeString,
@@ -70,7 +69,7 @@ describe("localizeString", () => {
         // Arrange
         const locale = "es";
         const content = "A simple path: /genwebpack/prod/en/foo.js";
-        const hashMap = {};
+        const hashMap: Record<string, any> = {};
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -89,7 +88,7 @@ describe("localizeString", () => {
         // Arrange
         const locale = "es";
         const content = "/genwebpack/prod/en/a.js /genwebpack/prod/en/b.js";
-        const hashMap = {};
+        const hashMap: Record<string, any> = {};
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -110,7 +109,7 @@ describe("localizeString", () => {
         // Arrange
         const locale = "es";
         const content = "/genwebpack/prod/pt/a.js /genwebpack/prod/hu/b.js";
-        const hashMap = {};
+        const hashMap: Record<string, any> = {};
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -133,7 +132,7 @@ describe("localizeString", () => {
         const content = "/genwebpack/prod/en/foo.3e083afe95f447481cad.js";
         const hashMap = {
             "3e083afe95f447481cad": "593cff1d8e1e383f2471",
-        };
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -158,7 +157,7 @@ describe("localizeString", () => {
         const hashMap = {
             "3e083afe95f447481cad": "593cff1d8e1e383f2471",
             "29d70669460257a74073": "9e0f5e0d0704dd61ee2f",
-        };
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -183,7 +182,7 @@ describe("localizeString", () => {
         const hashMap = {
             "3e083afe95f447481cad": "593cff1d8e1e383f2471",
             "29d70669460257a74073": "9e0f5e0d0704dd61ee2f",
-        };
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -208,7 +207,7 @@ describe("localizeString", () => {
         const hashMap = {
             "3e083afe95f447481cad": "593cff1d8e1e383f2471",
             "29d70669460257a74073": "9e0f5e0d0704dd61ee2f",
-        };
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -247,7 +246,9 @@ describe("localizeFile", () => {
         const content = "genwebpack/prod/en/file.2e083afe95f447481cad.js";
         const oldHash = "3e083afe95f447481cad";
         const locale = "es";
-        const hashMap = {"2e083afe95f447481cad": "4e083afe95f447481cad"};
+        const hashMap = {
+            "2e083afe95f447481cad": "4e083afe95f447481cad",
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -274,7 +275,9 @@ describe("localizeFile", () => {
         const content = "genwebpack/prod/en/file.2e083afe95f447481cad.js";
         const oldHash = "3e083afe95f447481cad";
         const locale = "es";
-        const hashMap = {"2e083afe95f447481cad": "4e083afe95f447481cad"};
+        const hashMap = {
+            "2e083afe95f447481cad": "4e083afe95f447481cad",
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -304,7 +307,7 @@ describe("localizeFile", () => {
         const hashMap = {
             "2e083afe95f447481cad": "4e083afe95f447481cad",
             c0ffee: "3e083afe95f447481cad",
-        };
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
@@ -332,7 +335,9 @@ describe("localizeFile", () => {
         const content = "genwebpack/prod/en/file.2e083afe95f447481cad.js";
         const oldHash = null;
         const locale = "es";
-        const hashMap = {"2e083afe95f447481cad": "4e083afe95f447481cad"};
+        const hashMap = {
+            "2e083afe95f447481cad": "4e083afe95f447481cad",
+        } as const;
         const getLocalePath = (locale: string) => `/prod/${locale}/`;
 
         // Act
diff --git a/packages/wonder-stuff-i18n/src/utils/__tests__/pofile-utils.test.js b/packages/wonder-stuff-i18n/src/utils/__tests__/pofile-utils.test.ts
similarity index 76%
rename from packages/wonder-stuff-i18n/src/utils/__tests__/pofile-utils.test.js
rename to packages/wonder-stuff-i18n/src/utils/__tests__/pofile-utils.test.ts
index 1f6dcaa7..d3bbba37 100644
--- a/packages/wonder-stuff-i18n/src/utils/__tests__/pofile-utils.test.js
+++ b/packages/wonder-stuff-i18n/src/utils/__tests__/pofile-utils.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import fs from "fs";
 import path from "path";
 
@@ -24,9 +23,10 @@ describe("buildPoItem", () => {
             type: "_",
             msgids: ["an extracted english string"],
             comments: [],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["an extracted english string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         const result = buildPoItem(fileName, extractedString);
 
         // Assert
@@ -58,9 +58,10 @@ describe("buildPoItem", () => {
             type: "ngettext",
             msgids: ["%(num)s english string", "%(num)s plural string"],
             comments: [],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "ngettext"; readonly msgids: readonly ["%(num)s english string", "%(num)s plural string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         const result = buildPoItem(fileName, extractedString);
 
         // Assert
@@ -94,9 +95,10 @@ describe("buildPoItem", () => {
             type: "_",
             msgids: ["an extracted english string %(name)s"],
             comments: [],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["an extracted english string %(name)s"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         const result = buildPoItem(fileName, extractedString);
 
         // Assert
@@ -130,9 +132,10 @@ describe("buildPoItem", () => {
             type: "_",
             msgids: ["an extracted english string"],
             comments: ["a simple comment"],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["an extracted english string"]; readonly comments: readonly ["a simple comment"]; }' is not assignable to parameter of type 'ExtractedString'.
         const result = buildPoItem(fileName, extractedString);
 
         // Assert
@@ -168,7 +171,8 @@ describe("mergePoItem", () => {
             type: "_",
             msgids: ["an extracted english string"],
             comments: [],
-        };
+        } as const;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["an extracted english string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         const item1 = buildPoItem(fileName1, extractedString1);
         const fileName2 = "test/some-file2.js";
         const extractedString2 = {
@@ -178,9 +182,10 @@ describe("mergePoItem", () => {
             type: "_",
             msgids: ["an extracted english string"],
             comments: [],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 12; readonly startOffset: 200; readonly endOffset: 229; readonly type: "_"; readonly msgids: readonly ["an extracted english string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         mergePoItem(item1, fileName2, extractedString2);
 
         // Assert
@@ -212,7 +217,8 @@ describe("mergePoItem", () => {
             type: "_",
             msgids: ["an extracted english string"],
             comments: ["comment 1"],
-        };
+        } as const;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["an extracted english string"]; readonly comments: readonly ["comment 1"]; }' is not assignable to parameter of type 'ExtractedString'.
         const item1 = buildPoItem(fileName1, extractedString1);
         const fileName2 = "test/some-file2.js";
         const extractedString2 = {
@@ -222,9 +228,10 @@ describe("mergePoItem", () => {
             type: "_",
             msgids: ["an extracted english string"],
             comments: ["comment 2"],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 12; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["an extracted english string"]; readonly comments: readonly ["comment 2"]; }' is not assignable to parameter of type 'ExtractedString'.
         mergePoItem(item1, fileName2, extractedString2);
 
         // Assert
@@ -259,7 +266,8 @@ describe("mergePoItem", () => {
             type: "ngettext",
             msgids: ["a singular string", "a plural string"],
             comments: [],
-        };
+        } as const;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "ngettext"; readonly msgids: readonly ["a singular string", "a plural string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         const item1 = buildPoItem(fileName1, extractedString1);
         const fileName2 = "test/some-file2.js";
         const extractedString2 = {
@@ -269,9 +277,10 @@ describe("mergePoItem", () => {
             type: "ngettext",
             msgids: ["a singular string", "a plural string"],
             comments: [],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 12; readonly startOffset: 200; readonly endOffset: 229; readonly type: "ngettext"; readonly msgids: readonly ["a singular string", "a plural string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         mergePoItem(item1, fileName2, extractedString2);
 
         // Assert
@@ -303,7 +312,8 @@ describe("mergePoItem", () => {
             type: "_",
             msgids: ["a singular string"],
             comments: [],
-        };
+        } as const;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 10; readonly startOffset: 100; readonly endOffset: 129; readonly type: "_"; readonly msgids: readonly ["a singular string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         const item1 = buildPoItem(fileName1, extractedString1);
         const fileName2 = "test/some-file2.js";
         const extractedString2 = {
@@ -313,15 +323,17 @@ describe("mergePoItem", () => {
             type: "ngettext",
             msgids: ["a singular string", "a plural string"],
             comments: [],
-        };
+        } as const;
         const errorSpy = jest
             .spyOn(console, "error")
             .mockImplementation(() => {});
         const exitSpy = jest
             .spyOn(process, "exit")
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '() => void' is not assignable to parameter of type '(code?: number | undefined) => never'.
             .mockImplementation(() => {});
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly linePos: 12; readonly startOffset: 200; readonly endOffset: 229; readonly type: "ngettext"; readonly msgids: readonly ["a singular string", "a plural string"]; readonly comments: readonly []; }' is not assignable to parameter of type 'ExtractedString'.
         mergePoItem(item1, fileName2, extractedString2);
 
         // Assert
diff --git a/packages/wonder-stuff-i18n/src/utils/emoji-for-locale.js b/packages/wonder-stuff-i18n/src/utils/emoji-for-locale.ts
similarity index 79%
rename from packages/wonder-stuff-i18n/src/utils/emoji-for-locale.js
rename to packages/wonder-stuff-i18n/src/utils/emoji-for-locale.ts
index fbdd0fd0..826697ee 100644
--- a/packages/wonder-stuff-i18n/src/utils/emoji-for-locale.js
+++ b/packages/wonder-stuff-i18n/src/utils/emoji-for-locale.ts
@@ -1,4 +1,3 @@
-// @flow
 /**
  * Provide an emoji to represent a locale.
  *
@@ -37,12 +36,13 @@ const LOCALE_TO_EMOJI_MAP = {
     ta: "🇱🇰", // Tamil -- Sri Lanka
     tr: "🇹🇷", // Turkish -- Turkey
     "zh-hans": "🇹🇼", // Mandarin -- Taiwan
-};
+} as const;
 
 /**
  * Given a locale, get an emoji representing that locale.
  *
  * @param {string} locale the locale string to get the emoji for
  */
+// @ts-expect-error [FEI-5011] - TS7053 - Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ readonly accents: "✨"; readonly bg: "🇧🇬"; readonly bn: "🇮🇳"; readonly boxes: "📦"; readonly cs: "🇨🇿"; readonly da: "🇩🇰"; readonly de: "🇩🇪"; readonly en: "🇬🇧"; readonly "en-pt": "☠️"; ... 22 more ...; readonly "zh-hans": "🇹🇼"; }'.
 export const getEmojiForLocale = (locale: string): string =>
     LOCALE_TO_EMOJI_MAP[locale] || "";
diff --git a/packages/wonder-stuff-i18n/src/utils/extract-i18n.js b/packages/wonder-stuff-i18n/src/utils/extract-i18n.ts
similarity index 96%
rename from packages/wonder-stuff-i18n/src/utils/extract-i18n.js
rename to packages/wonder-stuff-i18n/src/utils/extract-i18n.ts
index 1aeb5626..52e2e73c 100644
--- a/packages/wonder-stuff-i18n/src/utils/extract-i18n.js
+++ b/packages/wonder-stuff-i18n/src/utils/extract-i18n.ts
@@ -1,19 +1,17 @@
-// @flow
-
-export type ExtractedString = {|
+export type ExtractedString = {
     // The line number of the string in the original file.
-    linePos: number,
+    linePos: number;
     // The starting position of the string in the original file.
-    startOffset: number,
+    startOffset: number;
     // The ending position of the string in the original file.
-    endOffset: number,
+    endOffset: number;
     // The type of string, such as "_", "$_", or "ngettext".
-    type: string,
+    type: string;
     // The strings found (will be one for singular, two for plural)
-    msgids: Array<string>,
+    msgids: Array<string>;
     // The comments associated with the string.
-    comments: Array<string>,
-|};
+    comments: Array<string>;
+};
 
 // Used by the `re` function below, allowing for writing multi-line regexes
 // with comments.
@@ -31,7 +29,6 @@ const regexClean = (piece: string) =>
  * Builds a regex pattern (as a string) which can then be turned into a full
  * regex by calling: `new RegEx(...)`.
  */
-// $FlowIgnore Flow doesn't handled tagged template literals well.
 const re = ({raw}: any, ...interpolations: Array<string>) =>
     interpolations.reduce(
         (regex, insert, index) => regex + insert + regexClean(raw[index + 1]),
@@ -307,7 +304,7 @@ const STRIP_COMMENT_RE = new RegExp(
  * The second argument is an optional string which can be specified to leave a
  * comment intact (not remove it).
  */
-const stripJSComments = (jsCode: string, keep: ?string = null) =>
+const stripJSComments = (jsCode: string, keep: string | null = null) =>
     jsCode.replace(STRIP_COMMENT_RE, (match) =>
         keep != null && keep !== "" && match.includes(keep)
             ? match
@@ -337,7 +334,7 @@ const convertEscapes = (textString: string) =>
  */
 const extractAndCombineString = (textString: string): string => {
     // Look for the string segments (either double or single quote)
-    const parts = [];
+    const parts: Array<string> = [];
     for (const match of textString.matchAll(INNER_STRINGS_RE)) {
         parts.push(match[1] || match[2]);
     }
@@ -378,6 +375,7 @@ const extractAndCombineComment = (commentString: string): Array<string> => {
             comments.push(comment.replace(/I18N:\s*/, "").trim());
         } else if (comment.trim()) {
             // Or is this just appending to an existing comment?
+            // @ts-expect-error [FEI-5011] - TS7022 - 'oldComment' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
             const oldComment = comments[comments.length - 1];
             comments[comments.length - 1] =
                 (oldComment ? oldComment + " " : "") + comment.trim();
@@ -488,6 +486,7 @@ export function* extractStrings(
             const endOffset =
                 textString.indexOf(
                     groups.ngettext_plural,
+                    // @ts-expect-error [FEI-5011] - TS2532 - Object is possibly 'undefined'.
                     match.index + groups.ngettext_singular.length,
                 ) + groups.ngettext_plural.length;
             yield {
diff --git a/packages/wonder-stuff-i18n/src/utils/i18n-utils.js b/packages/wonder-stuff-i18n/src/utils/i18n-utils.ts
similarity index 88%
rename from packages/wonder-stuff-i18n/src/utils/i18n-utils.js
rename to packages/wonder-stuff-i18n/src/utils/i18n-utils.ts
index 09bb8eb1..2bc2672d 100644
--- a/packages/wonder-stuff-i18n/src/utils/i18n-utils.js
+++ b/packages/wonder-stuff-i18n/src/utils/i18n-utils.ts
@@ -1,7 +1,7 @@
-// @flow
 import fs from "fs";
 import path from "path";
 
+// @ts-expect-error [FEI-5011] - TS7016 - Could not find a declaration file for module 'ancesdir'. '/Users/kevinbarabash/khan/wonder-stuff/node_modules/ancesdir/dist/index.js' implicitly has an 'any' type.
 import ancesdir from "ancesdir";
 
 import {extractStrings} from "./extract-i18n";
@@ -9,7 +9,12 @@ import {extractStrings} from "./extract-i18n";
 import type {ExtractedString} from "./extract-i18n";
 
 export type TranslatedLocaleStrings = {
-    [msgid: string]: string | {|lang: string, messages: Array<string>|},
+    [msgid: string]:
+        | string
+        | {
+              lang: string;
+              messages: Array<string>;
+          };
 };
 
 /**
@@ -35,7 +40,7 @@ export const getIgnoreGlobs = (
                 // Remove empty strings
                 .filter((line) => !!line)
         );
-    } catch (e) {
+    } catch (e: any) {
         // If the file doesn't exist, then we're not ignoring any files.
         return [];
     }
@@ -51,7 +56,7 @@ export const getIgnoreGlobs = (
 export const getI18nStringsFromString = (
     textString: string,
 ): Array<ExtractedString> => {
-    const strings = [];
+    const strings: Array<ExtractedString> = [];
 
     // Get all the strings that need to be replaced, but in reverse
     // order, so that it's easier to insert them in the right place.
@@ -80,7 +85,7 @@ export const translateString = (
     // If no pre-parsed strings where provided, then we need to parse them
     // (providing pre-parsed strings can be a performance optimization,
     // especially if you're translating a file into multiple languages).
-    strings?: Array<ExtractedString> = getI18nStringsFromString(textString),
+    strings: Array<ExtractedString> = getI18nStringsFromString(textString),
 ): string => {
     let translatedSource = textString;
 
diff --git a/packages/wonder-stuff-i18n/src/utils/localize-file.js b/packages/wonder-stuff-i18n/src/utils/localize-file.ts
similarity index 92%
rename from packages/wonder-stuff-i18n/src/utils/localize-file.js
rename to packages/wonder-stuff-i18n/src/utils/localize-file.ts
index 9a57c894..7db3bafd 100644
--- a/packages/wonder-stuff-i18n/src/utils/localize-file.js
+++ b/packages/wonder-stuff-i18n/src/utils/localize-file.ts
@@ -1,4 +1,3 @@
-// @flow
 /**
  * Utility that localizes Webpack-generated files with the correct public
  * path to properly handle dynamic loading of bundles. Used by
@@ -58,10 +57,15 @@ export const localizeString = ({
     hashMap,
     getLocalePath,
 }: {
-    locale: string,
-    content: string,
-    hashMap?: ?{[string]: string},
-    getLocalePath: (string) => string,
+    locale: string;
+    content: string;
+    hashMap?:
+        | {
+              [key: string]: string;
+          }
+        | null
+        | undefined;
+    getLocalePath: (arg1: string) => string;
 }): string => {
     // Replace all English paths with the path to the locale
     const newContent = content.replace(
@@ -105,11 +109,13 @@ export const localizeFile = ({
     hashMap,
     getLocalePath,
 }: {
-    content: string,
-    locale: string,
-    oldHash: ?string,
-    hashMap: {[string]: string},
-    getLocalePath: (string) => string,
+    content: string;
+    locale: string;
+    oldHash: string | null | undefined;
+    hashMap: {
+        [key: string]: string;
+    };
+    getLocalePath: (arg1: string) => string;
 }): string => {
     const newContent = localizeString({
         locale,
diff --git a/packages/wonder-stuff-i18n/src/utils/pofile-utils.js b/packages/wonder-stuff-i18n/src/utils/pofile-utils.ts
similarity index 92%
rename from packages/wonder-stuff-i18n/src/utils/pofile-utils.js
rename to packages/wonder-stuff-i18n/src/utils/pofile-utils.ts
index 6bcab510..3f61555a 100644
--- a/packages/wonder-stuff-i18n/src/utils/pofile-utils.js
+++ b/packages/wonder-stuff-i18n/src/utils/pofile-utils.ts
@@ -1,4 +1,3 @@
-// @flow
 import fs from "fs";
 import path from "path";
 
@@ -10,13 +9,15 @@ import {getIgnoreGlobs} from "./i18n-utils";
 
 import type {ExtractedString} from "./extract-i18n";
 
-type POItem = {|
-    msgid: string,
-    msgid_plural: string,
-    flags: {[string]: boolean},
-    references: Array<string>,
-    extractedComments: Array<string>,
-|};
+type POItem = {
+    msgid: string;
+    msgid_plural: string;
+    flags: {
+        [key: string]: boolean;
+    };
+    references: Array<string>;
+    extractedComments: Array<string>;
+};
 
 /**
  * Construct a POItem from a filename and extracted string.
@@ -30,6 +31,7 @@ export const buildPoItem = (
     {linePos, type, msgids: [msgid, plural], comments}: ExtractedString,
 ): POItem => {
     // If we haven't seen this string before we build a PO Item.
+    // @ts-expect-error [FEI-5011] - TS2322 - Type 'Item' is not assignable to type 'POItem'.
     const poItem: POItem = new PO.Item();
 
     // Add the primary string
@@ -164,6 +166,7 @@ export const getPOTFileStringFromFiles = (files: Array<string>): string => {
 
     // Normally items would be an array, but we can get away with passing in
     // the map as internally pofile will just iterate through the items.
+    // @ts-expect-error [FEI-5011] - TS2740 - Type 'Map<string, POItem>' is missing the following properties from type 'Item[]': length, pop, push, concat, and 24 more.
     potfile.items = getPoItemMap(files);
 
     return potfile.toString();
diff --git a/packages/wonder-stuff-sentry/src/__tests__/__snapshots__/kind-error-data.test.js.snap b/packages/wonder-stuff-sentry/src/__tests__/__snapshots__/kind-error-data.test.ts.snap
similarity index 100%
rename from packages/wonder-stuff-sentry/src/__tests__/__snapshots__/kind-error-data.test.js.snap
rename to packages/wonder-stuff-sentry/src/__tests__/__snapshots__/kind-error-data.test.ts.snap
diff --git a/packages/wonder-stuff-sentry/src/__tests__/collate-sentry-data.test.js b/packages/wonder-stuff-sentry/src/__tests__/collate-sentry-data.test.ts
similarity index 97%
rename from packages/wonder-stuff-sentry/src/__tests__/collate-sentry-data.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/collate-sentry-data.test.ts
index 4d3609a8..4a175bbf 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/collate-sentry-data.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/collate-sentry-data.test.ts
@@ -1,11 +1,10 @@
-// @flow
 import {KindError} from "@khanacademy/wonder-stuff-core";
 import {KindSentryError} from "../kind-sentry-error";
 import {collateSentryData} from "../collate-sentry-data";
 import {DefaultKindErrorDataOptions} from "../default-kind-error-data-options";
 import * as NormalizeSentryData from "../normalize-sentry-data";
 
-jest.mock("../normalize-sentry-data.js", () =>
+jest.mock("../normalize-sentry-data", () =>
     jest.requireActual("../normalize-sentry-data"),
 );
 
@@ -80,7 +79,7 @@ describe("#collateSentryData", () => {
                 kindTagName: "KIND_TAG",
                 groupByTagName: "GROUP_BY_TAG",
                 concatenatedMessageTagName: "CONCATENATED_MESSAGE_TAG",
-            };
+            } as const;
 
             // Act
             const result = collateSentryData(options, error);
@@ -150,7 +149,7 @@ describe("#collateSentryData", () => {
             const options = {
                 ...DefaultKindErrorDataOptions,
                 causalErrorContextPrefix: "CAUSE",
-            };
+            } as const;
 
             // Act
             const result = collateSentryData(options, error);
@@ -227,6 +226,7 @@ describe("#collateSentryData", () => {
             );
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toIncludeSameMembers' does not exist on type 'JestMatchers<SentryFingerprint>'.
             expect(result.fingerprint).toIncludeSameMembers([
                 "CAUSE1FINGERPRINT",
                 "CAUSE2FINGERPRINT",
@@ -291,7 +291,7 @@ describe("#collateSentryData", () => {
                 kindTagName: "KIND_TAG",
                 groupByTagName: "GROUP_BY_TAG",
                 concatenatedMessageTagName: "CONCATENATED_MESSAGE_TAG",
-            };
+            } as const;
 
             // Act
             const result = collateSentryData(options, error);
@@ -383,7 +383,7 @@ describe("#collateSentryData", () => {
             const options = {
                 ...DefaultKindErrorDataOptions,
                 causalErrorContextPrefix: "CAUSE",
-            };
+            } as const;
 
             // Act
             const result = collateSentryData(options, error);
@@ -470,6 +470,7 @@ describe("#collateSentryData", () => {
             );
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toIncludeSameMembers' does not exist on type 'JestMatchers<SentryFingerprint>'.
             expect(result.fingerprint).toIncludeSameMembers([
                 "ROOTFINGERPRINT",
                 "CAUSE2FINGERPRINT",
diff --git a/packages/wonder-stuff-sentry/src/__tests__/get-sentry-data-from-error.test.js b/packages/wonder-stuff-sentry/src/__tests__/get-sentry-data-from-error.test.ts
similarity index 75%
rename from packages/wonder-stuff-sentry/src/__tests__/get-sentry-data-from-error.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/get-sentry-data-from-error.test.ts
index b24cdf0c..51f8ae35 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/get-sentry-data-from-error.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/get-sentry-data-from-error.test.ts
@@ -1,11 +1,10 @@
-// @flow
 import {KindSentryError} from "../kind-sentry-error";
 import {getSentryDataFromError} from "../get-sentry-data-from-error";
 
 describe("#getSentryDataFromError", () => {
     it.each([null, undefined, new Error("test")])(
         "should return null for a non-KindSentryError value like %s",
-        (error) => {
+        (error: any) => {
             // Arrange
 
             // Act
@@ -28,8 +27,9 @@ describe("#getSentryDataFromError", () => {
                 },
             },
             fingerprint: ["fingerprint1"],
-        };
+        } as const;
         const error = new KindSentryError("test", "CUSTOM_KIND", {
+            // @ts-expect-error [FEI-5011] - TS2322 - Type '{ readonly tags: { readonly tag1: "tagValue1"; }; readonly contexts: { readonly context1: { readonly context1Key1: "context1Value1"; }; }; readonly fingerprint: readonly ["fingerprint1"]; }' is not assignable to type 'Partial<SentryData>'.
             sentryData,
         });
 
diff --git a/packages/wonder-stuff-sentry/src/__tests__/is-reserved-context-property.test.js b/packages/wonder-stuff-sentry/src/__tests__/is-reserved-context-property.test.ts
similarity index 68%
rename from packages/wonder-stuff-sentry/src/__tests__/is-reserved-context-property.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/is-reserved-context-property.test.ts
index ed72f1c2..1be28e69 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/is-reserved-context-property.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/is-reserved-context-property.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {isReservedContextProperty} from "../is-reserved-context-property";
 
 describe("#isReservedContextProperty", () => {
@@ -9,6 +8,7 @@ describe("#isReservedContextProperty", () => {
         const result = isReservedContextProperty("foo");
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2551 - Property 'toBeFalse' does not exist on type 'JestMatchers<boolean>'. Did you mean 'toBeFalsy'?
         expect(result).toBeFalse();
     });
 
@@ -19,6 +19,7 @@ describe("#isReservedContextProperty", () => {
         const result = isReservedContextProperty("type");
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeTrue' does not exist on type 'JestMatchers<boolean>'.
         expect(result).toBeTrue();
     });
 });
diff --git a/packages/wonder-stuff-sentry/src/__tests__/is-reserved-tag-key.test.js b/packages/wonder-stuff-sentry/src/__tests__/is-reserved-tag-key.test.ts
similarity index 73%
rename from packages/wonder-stuff-sentry/src/__tests__/is-reserved-tag-key.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/is-reserved-tag-key.test.ts
index b4147ba3..37de7aaa 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/is-reserved-tag-key.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/is-reserved-tag-key.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {DefaultKindErrorDataOptions} from "../default-kind-error-data-options";
 import {isReservedTagKey} from "../is-reserved-tag-key";
 
@@ -10,6 +9,7 @@ describe("#isReservedTagKey", () => {
         const result = isReservedTagKey(DefaultKindErrorDataOptions, "foo");
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2551 - Property 'toBeFalse' does not exist on type 'JestMatchers<boolean>'. Did you mean 'toBeFalsy'?
         expect(result).toBeFalse();
     });
 
@@ -23,6 +23,7 @@ describe("#isReservedTagKey", () => {
         );
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeTrue' does not exist on type 'JestMatchers<boolean>'.
         expect(result).toBeTrue();
     });
 });
diff --git a/packages/wonder-stuff-sentry/src/__tests__/is-tag-key-valid.test.js b/packages/wonder-stuff-sentry/src/__tests__/is-tag-key-valid.test.ts
similarity index 66%
rename from packages/wonder-stuff-sentry/src/__tests__/is-tag-key-valid.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/is-tag-key-valid.test.ts
index d754f3d5..2e8a902e 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/is-tag-key-valid.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/is-tag-key-valid.test.ts
@@ -1,29 +1,30 @@
-// @flow
 import {isTagKeyValid} from "../is-tag-key-valid";
 
 describe("#isTagKeyValid", () => {
     it.each([undefined, "", Array(33).fill("a").join("")])(
         "should return false if a key is not valid (%s)",
-        (testPoint) => {
+        (testPoint: any) => {
             // Arrange
 
             // Act
             const result = isTagKeyValid(testPoint);
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2551 - Property 'toBeFalse' does not exist on type 'JestMatchers<boolean>'. Did you mean 'toBeFalsy'?
             expect(result).toBeFalse();
         },
     );
 
     it.each(["a", Array(32).fill("a").join("")])(
         "should return true if a key is valid (%s)",
-        (testPoint) => {
+        (testPoint: any) => {
             // Arrange
 
             // Act
             const result = isTagKeyValid(testPoint);
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeTrue' does not exist on type 'JestMatchers<boolean>'.
             expect(result).toBeTrue();
         },
     );
diff --git a/packages/wonder-stuff-sentry/src/__tests__/kind-error-data.test.js b/packages/wonder-stuff-sentry/src/__tests__/kind-error-data.test.ts
similarity index 84%
rename from packages/wonder-stuff-sentry/src/__tests__/kind-error-data.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/kind-error-data.test.ts
index fca3683d..4e0bc7cc 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/kind-error-data.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/kind-error-data.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as CollateSentryData from "../collate-sentry-data";
 import {DefaultKindErrorDataOptions} from "../default-kind-error-data-options";
 import {EmptySentryData} from "../empty-sentry-data";
@@ -28,15 +27,18 @@ describe("KindErrorData", () => {
                     groupByTagName: `${INVALID_TAG_NAME}-group-by`,
                     concatenatedMessageTagName: `${INVALID_TAG_NAME}-concatenated-message`,
                 },
-            ])("should throw if options are invalid (%s)", (badOptions) => {
-                // Arrange
+            ])(
+                "should throw if options are invalid (%s)",
+                (badOptions: any) => {
+                    // Arrange
 
-                // Act
-                const act = () => new KindErrorData(badOptions);
+                    // Act
+                    const act = () => new KindErrorData(badOptions);
 
-                // Assert
-                expect(act).toThrowErrorMatchingSnapshot();
-            });
+                    // Assert
+                    expect(act).toThrowErrorMatchingSnapshot();
+                },
+            );
         });
 
         describe("when built for production", () => {
@@ -53,15 +55,18 @@ describe("KindErrorData", () => {
                     groupByTagName: `${INVALID_TAG_NAME}-group-by`,
                     concatenatedMessageTagName: `${INVALID_TAG_NAME}-concatenated-message`,
                 },
-            ])("should not throw if options are invalid (%s)", (badOptions) => {
-                // Arrange
+            ])(
+                "should not throw if options are invalid (%s)",
+                (badOptions: any) => {
+                    // Arrange
 
-                // Act
-                const act = () => new KindErrorData(badOptions);
+                    // Act
+                    const act = () => new KindErrorData(badOptions);
 
-                // Assert
-                expect(act).not.toThrowError("Invalid options");
-            });
+                    // Assert
+                    expect(act).not.toThrowError("Invalid options");
+                },
+            );
         });
 
         it("should include information when throwing about invalid options", async () => {
@@ -70,14 +75,14 @@ describe("KindErrorData", () => {
                 kindTagName: `${INVALID_TAG_NAME}-kind`,
                 groupByTagName: `${INVALID_TAG_NAME}-group-by`,
                 concatenatedMessageTagName: `${INVALID_TAG_NAME}-concatenated-message`,
-            };
+            } as const;
 
             // Act
-            const act = new Promise((resolve, reject) => {
+            const act = new Promise((resolve: any, reject: any) => {
                 try {
                     // Should not resolve!
                     resolve(new KindErrorData(badOptions));
-                } catch (e) {
+                } catch (e: any) {
                     reject(e);
                 }
             });
@@ -127,7 +132,7 @@ describe("KindErrorData", () => {
                 const event = {
                     kind: "event",
                     event_id: "event-id",
-                };
+                } as const;
 
                 // Act
                 const result = registeredProcessor(event);
@@ -146,18 +151,18 @@ describe("KindErrorData", () => {
                 });
                 const enhanceSpy = jest
                     .spyOn(underTest, "enhanceEventWithErrorData")
+                    // @ts-expect-error [FEI-5011] - TS2559 - Type '"ENHANCED"' has no properties in common with type 'SentryEvent'.
                     .mockReturnValue("ENHANCED");
-                // $FlowIgnore[escaped-generic]
                 underTest.setupOnce(addGlobalEventProcessorMock, getHub);
                 const registeredProcessor =
                     addGlobalEventProcessorMock.mock.calls[0][0];
                 const event = {
                     kind: "event",
                     event_id: "event-id",
-                };
+                } as const;
                 const hint = {
                     event_id: "event-id",
-                };
+                } as const;
 
                 // Act
                 const result = registeredProcessor(event, hint);
@@ -178,17 +183,17 @@ describe("KindErrorData", () => {
             },
         ])(
             "should return the event if the original exception (%s) is not an Error",
-            (originalException) => {
+            (originalException: any) => {
                 // Arrange
                 const underTest = new KindErrorData();
                 const event = {
                     kind: "event",
                     event_id: "event-id",
-                };
+                } as const;
                 const hint = {
                     event_id: "event-id",
                     originalException,
-                };
+                } as const;
 
                 // Act
                 const result = underTest.enhanceEventWithErrorData(event, hint);
@@ -204,7 +209,7 @@ describe("KindErrorData", () => {
             const event = {
                 kind: "event",
                 event_id: "event-id",
-            };
+            } as const;
 
             // Act
             const result = underTest.enhanceEventWithErrorData(event);
@@ -219,16 +224,16 @@ describe("KindErrorData", () => {
                 ...DefaultKindErrorDataOptions,
                 groupByTagName: "GROUP",
                 kindTagName: "KIND",
-            };
+            } as const;
             const underTest = new KindErrorData(options);
             const event = {
                 kind: "event",
                 event_id: "event-id",
-            };
+            } as const;
             const hint = {
                 event_id: "event-id",
                 originalException: new Error("original-exception"),
-            };
+            } as const;
             const collateSentryDataSpy = jest
                 .spyOn(CollateSentryData, "collateSentryData")
                 .mockReturnValue(EmptySentryData);
@@ -249,7 +254,7 @@ describe("KindErrorData", () => {
                 ...DefaultKindErrorDataOptions,
                 groupByTagName: "GROUP",
                 kindTagName: "KIND",
-            };
+            } as const;
             const underTest = new KindErrorData(options);
             const event = {
                 kind: "event",
@@ -267,11 +272,11 @@ describe("KindErrorData", () => {
                     },
                 },
                 fingerprint: ["originalFingerprint"],
-            };
+            } as const;
             const hint = {
                 event_id: "event-id",
                 originalException: new Error("original-exception"),
-            };
+            } as const;
             jest.spyOn(CollateSentryData, "collateSentryData").mockReturnValue({
                 tags: {
                     tag1: "tag1-value",
@@ -285,6 +290,7 @@ describe("KindErrorData", () => {
             });
 
             // Act
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly kind: "event"; readonly event_id: "event-id"; readonly tags: { readonly tag1: "originalValue1"; readonly tag2: "originalValue2"; }; readonly contexts: { readonly context1: { readonly key1: "originalValue1"; }; readonly context2: { ...; }; }; readonly fingerprint: readonly [...]; }' is not assignable to parameter of type 'SentryEvent'.
             const result = underTest.enhanceEventWithErrorData(event, hint);
 
             // Assert
diff --git a/packages/wonder-stuff-sentry/src/__tests__/kind-sentry-error.test.js b/packages/wonder-stuff-sentry/src/__tests__/kind-sentry-error.test.ts
similarity index 92%
rename from packages/wonder-stuff-sentry/src/__tests__/kind-sentry-error.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/kind-sentry-error.test.ts
index ee54e187..d4895967 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/kind-sentry-error.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/kind-sentry-error.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors} from "@khanacademy/wonder-stuff-core";
 import type {Metadata} from "@khanacademy/wonder-stuff-core";
 import {KindSentryError} from "../kind-sentry-error";
@@ -13,6 +12,7 @@ describe("KindSentryError", () => {
             const {name: result} = new KindSentryError("MESSAGE", "KIND");
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toEndWith' does not exist on type 'JestMatchers<string>'.
             expect(result).toEndWith("SentryError");
         });
 
@@ -25,6 +25,7 @@ describe("KindSentryError", () => {
             });
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toEndWith' does not exist on type 'JestMatchers<string>'.
             expect(result).toEndWith("NAMEError");
         });
 
@@ -37,6 +38,7 @@ describe("KindSentryError", () => {
             });
 
             // Assert
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'toStartWith' does not exist on type 'JestMatchers<string>'.
             expect(result).toStartWith("PREFIX");
         });
 
@@ -75,7 +77,7 @@ describe("KindSentryError", () => {
             const metadata: Metadata = {
                 some: "metadata",
             };
-            const sentryData: $Partial<SentryData> = {
+            const sentryData: Partial<SentryData> = {
                 tags: {
                     tag1: "tagvalue1",
                 },
@@ -108,7 +110,7 @@ describe("KindSentryError", () => {
             const metadata: Metadata = {
                 some: "metadata",
             };
-            const sentryData: $Partial<SentryData> = {
+            const sentryData: Partial<SentryData> = {
                 tags: {
                     tag1: "tagvalue1",
                 },
diff --git a/packages/wonder-stuff-sentry/src/__tests__/normalize-sentry-data.test.js b/packages/wonder-stuff-sentry/src/__tests__/normalize-sentry-data.test.ts
similarity index 90%
rename from packages/wonder-stuff-sentry/src/__tests__/normalize-sentry-data.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/normalize-sentry-data.test.ts
index 2a2b4b3f..7a1cab0f 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/normalize-sentry-data.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/normalize-sentry-data.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {DefaultKindErrorDataOptions} from "../default-kind-error-data-options";
 import {normalizeSentryData} from "../normalize-sentry-data";
 import * as TruncateTagValue from "../truncate-tag-value";
@@ -22,7 +21,7 @@ describe("#normalizeSentryData", () => {
                 tags: {
                     "": "value1",
                 },
-            };
+            } as const;
 
             // Act
             const result = () =>
@@ -40,7 +39,7 @@ describe("#normalizeSentryData", () => {
                 tags: {
                     [DefaultKindErrorDataOptions.kindTagName]: "value1",
                 },
-            };
+            } as const;
 
             // Act
             const result = () =>
@@ -60,7 +59,7 @@ describe("#normalizeSentryData", () => {
                         type: "value1",
                     },
                 },
-            };
+            } as const;
 
             // Act
             const result = () =>
@@ -84,7 +83,7 @@ describe("#normalizeSentryData", () => {
                 tags: {
                     "": "value1",
                 },
-            };
+            } as const;
 
             // Act
             const result = () =>
@@ -100,7 +99,7 @@ describe("#normalizeSentryData", () => {
                 tags: {
                     [DefaultKindErrorDataOptions.kindTagName]: "value1",
                 },
-            };
+            } as const;
 
             // Act
             const result = () =>
@@ -118,7 +117,7 @@ describe("#normalizeSentryData", () => {
                         type: "value1",
                     },
                 },
-            };
+            } as const;
 
             // Act
             const result = () =>
@@ -151,15 +150,15 @@ describe("#normalizeSentryData", () => {
                     notReservedAtAll: "value7",
                 },
             },
-        };
+        } as const;
 
         // Act
-        const act = new Promise((resolve, reject) => {
+        const act = new Promise((resolve: any, reject: any) => {
             try {
                 normalizeSentryData(DefaultKindErrorDataOptions, data);
                 // Should never resolve!
                 resolve();
-            } catch (e) {
+            } catch (e: any) {
                 reject(e);
             }
         });
@@ -192,7 +191,7 @@ describe("#normalizeSentryData", () => {
             tags: {
                 tag1: "Untruncated",
             },
-        };
+        } as const;
 
         // Act
         const {tags: result} = normalizeSentryData(
@@ -209,7 +208,7 @@ describe("#normalizeSentryData", () => {
     it("should return the validated sentry data", () => {
         // Arrange
         jest.spyOn(TruncateTagValue, "truncateTagValue").mockImplementation(
-            (t) => t,
+            (t: any) => t,
         );
         const data = {
             tags: {
@@ -225,9 +224,10 @@ describe("#normalizeSentryData", () => {
                 },
             },
             fingerprint: ["fingerprint1", "fingerprint2"],
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly tags: { readonly tag1: "tag1Value"; readonly tag2: "tag2Value"; }; readonly contexts: { readonly contextOne: { readonly iAm: "a context"; }; readonly contextTwo: { readonly iAmAlso: "a context"; }; }; readonly fingerprint: readonly [...]; }' is not assignable to parameter of type 'Readonly<Partial<SentryData>>'.
         const result = normalizeSentryData(DefaultKindErrorDataOptions, data);
 
         // Assert
@@ -243,7 +243,7 @@ describe("#normalizeSentryData", () => {
         {contexts: {aMissingContext: undefined}},
     ])(
         "should set defaults for data not included in the data given to be validated (%s)",
-        (testPoint) => {
+        (testPoint: any) => {
             // Arrange
 
             // Act
diff --git a/packages/wonder-stuff-sentry/src/__tests__/sentry-data-reducer.test.js b/packages/wonder-stuff-sentry/src/__tests__/sentry-data-reducer.test.ts
similarity index 99%
rename from packages/wonder-stuff-sentry/src/__tests__/sentry-data-reducer.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/sentry-data-reducer.test.ts
index 49a47427..ea380a12 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/sentry-data-reducer.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/sentry-data-reducer.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {sentryDataReducer} from "../sentry-data-reducer";
 import {EmptySentryData} from "../empty-sentry-data";
 import {DefaultKindErrorDataOptions} from "../default-kind-error-data-options";
@@ -9,7 +8,7 @@ describe("#sentryDataReducer", () => {
     describe("index is zero", () => {
         it.each([null, EmptySentryData])(
             "should return the accumulator when error has no sentry data",
-            (sentryData) => {
+            (sentryData: any) => {
                 // Arrange
                 const accumulator: SentryData = {
                     tags: {
@@ -154,7 +153,7 @@ describe("#sentryDataReducer", () => {
             const options = {
                 ...DefaultKindErrorDataOptions,
                 causalErrorContextPrefix: "custom-context-name",
-            };
+            } as const;
             const accumulator: SentryData = {
                 tags: {
                     tag1: "value1",
diff --git a/packages/wonder-stuff-sentry/src/__tests__/truncate-tag-value.test.js b/packages/wonder-stuff-sentry/src/__tests__/truncate-tag-value.test.ts
similarity index 95%
rename from packages/wonder-stuff-sentry/src/__tests__/truncate-tag-value.test.js
rename to packages/wonder-stuff-sentry/src/__tests__/truncate-tag-value.test.ts
index 8611021a..7b1d9f3d 100644
--- a/packages/wonder-stuff-sentry/src/__tests__/truncate-tag-value.test.js
+++ b/packages/wonder-stuff-sentry/src/__tests__/truncate-tag-value.test.ts
@@ -1,10 +1,9 @@
-// @flow
 import {truncateTagValue} from "../truncate-tag-value";
 
 describe("#truncateTagValue", () => {
     it.each(["", "ABCDEFGHIJK", Array(200).fill("a").join("")])(
         "should not truncate tag values that do not need it (%s)",
-        (testPoint) => {
+        (testPoint: any) => {
             // Arrange
 
             // Act
diff --git a/packages/wonder-stuff-sentry/src/collate-sentry-data.js b/packages/wonder-stuff-sentry/src/collate-sentry-data.ts
similarity index 90%
rename from packages/wonder-stuff-sentry/src/collate-sentry-data.js
rename to packages/wonder-stuff-sentry/src/collate-sentry-data.ts
index 2464046f..80eb07c3 100644
--- a/packages/wonder-stuff-sentry/src/collate-sentry-data.js
+++ b/packages/wonder-stuff-sentry/src/collate-sentry-data.ts
@@ -1,4 +1,3 @@
-// @flow
 import {
     errorsFromError,
     Order,
@@ -34,10 +33,11 @@ import type {SentryData, KindErrorDataOptions} from "./types";
 export const collateSentryData = (
     options: KindErrorDataOptions,
     error: Error,
-): $ReadOnly<SentryData> => {
+): Readonly<SentryData> => {
     // First, get all the errors in the stack.
     const errors = errorsFromError(error, Order.ConsequenceFirst);
-    const consquenceAndCauses: $ReadOnlyArray<Error> = Array.from(errors);
+    // @ts-expect-error [FEI-5011] - TS2769 - No overload matches this call.
+    const consquenceAndCauses: ReadonlyArray<Error> = Array.from(errors);
 
     // Now, we need to collate this stack as follows:
     // 1. Any sentryData they hold has to be merged into the collatedData from
@@ -45,7 +45,7 @@ export const collateSentryData = (
     //    take precedent.
     // 2. Errors, regardless of whether they have sentryData, need to be
     //    given their own context in the data.
-    const rawCollatedData: $ReadOnly<SentryData> =
+    const rawCollatedData: Readonly<SentryData> =
         consquenceAndCauses.reduceRight(
             (acc, value, index) =>
                 sentryDataReducer(options, acc, value, index),
@@ -81,8 +81,9 @@ export const collateSentryData = (
         ...collatedData.tags,
         [kindTagName]: truncateTagValue(kindTag),
         [concatenatedMessageTagName]: truncateTagValue(concatenatedMessageTag),
-    };
+    } as const;
     if (groupByTag.length) {
+        // @ts-expect-error [FEI-5011] - TS2542 - Index signature in type '{ readonly [x: string]: string; }' only permits reading.
         tags[groupByTagName] = truncateTagValue(groupByTag);
     }
 
diff --git a/packages/wonder-stuff-sentry/src/default-kind-error-data-options.js b/packages/wonder-stuff-sentry/src/default-kind-error-data-options.ts
similarity index 97%
rename from packages/wonder-stuff-sentry/src/default-kind-error-data-options.js
rename to packages/wonder-stuff-sentry/src/default-kind-error-data-options.ts
index 057e43c5..2aa6b3fe 100644
--- a/packages/wonder-stuff-sentry/src/default-kind-error-data-options.js
+++ b/packages/wonder-stuff-sentry/src/default-kind-error-data-options.ts
@@ -1,4 +1,3 @@
-// @flow
 import type {KindErrorDataOptions} from "./types";
 
 /**
diff --git a/packages/wonder-stuff-sentry/src/empty-sentry-data.js b/packages/wonder-stuff-sentry/src/empty-sentry-data.ts
similarity index 63%
rename from packages/wonder-stuff-sentry/src/empty-sentry-data.js
rename to packages/wonder-stuff-sentry/src/empty-sentry-data.ts
index 479d69a1..7905456d 100644
--- a/packages/wonder-stuff-sentry/src/empty-sentry-data.js
+++ b/packages/wonder-stuff-sentry/src/empty-sentry-data.ts
@@ -1,10 +1,9 @@
-// @flow
 import type {SentryData} from "./types";
 
 /**
  * An empty sentry data object.
  */
-export const EmptySentryData: $ReadOnly<SentryData> = Object.freeze({
+export const EmptySentryData: Readonly<SentryData> = Object.freeze({
     tags: {},
     contexts: {},
     fingerprint: [],
diff --git a/packages/wonder-stuff-sentry/src/get-sentry-data-from-error.js b/packages/wonder-stuff-sentry/src/get-sentry-data-from-error.ts
similarity index 91%
rename from packages/wonder-stuff-sentry/src/get-sentry-data-from-error.js
rename to packages/wonder-stuff-sentry/src/get-sentry-data-from-error.ts
index ede44d7b..30bfbab8 100644
--- a/packages/wonder-stuff-sentry/src/get-sentry-data-from-error.js
+++ b/packages/wonder-stuff-sentry/src/get-sentry-data-from-error.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindSentryError} from "./kind-sentry-error";
 import type {SentryData} from "./types";
 
@@ -11,7 +10,7 @@ import type {SentryData} from "./types";
  */
 export const getSentryDataFromError = (
     error: Error,
-): ?$ReadOnly<SentryData> => {
+): Readonly<SentryData> | null | undefined => {
     if (error instanceof KindSentryError) {
         return error.sentryData;
     }
diff --git a/packages/wonder-stuff-sentry/src/index.js b/packages/wonder-stuff-sentry/src/index.ts
similarity index 96%
rename from packages/wonder-stuff-sentry/src/index.js
rename to packages/wonder-stuff-sentry/src/index.ts
index 500f150a..1a42e574 100644
--- a/packages/wonder-stuff-sentry/src/index.js
+++ b/packages/wonder-stuff-sentry/src/index.ts
@@ -1,4 +1,3 @@
-// @flow
 export {KindSentryError} from "./kind-sentry-error";
 export {KindErrorData} from "./kind-error-data";
 
diff --git a/packages/wonder-stuff-sentry/src/is-reserved-context-property.js b/packages/wonder-stuff-sentry/src/is-reserved-context-property.ts
similarity index 98%
rename from packages/wonder-stuff-sentry/src/is-reserved-context-property.js
rename to packages/wonder-stuff-sentry/src/is-reserved-context-property.ts
index 08c6a7be..0a5dc008 100644
--- a/packages/wonder-stuff-sentry/src/is-reserved-context-property.js
+++ b/packages/wonder-stuff-sentry/src/is-reserved-context-property.ts
@@ -1,4 +1,3 @@
-// @flow
 // From:
 // https://docs.sentry.io/platforms/python/guides/logging/enriching-events/context/
 const RESERVED_CONTEXT_PROPERTIES = new Set(["type"]);
diff --git a/packages/wonder-stuff-sentry/src/is-reserved-tag-key.js b/packages/wonder-stuff-sentry/src/is-reserved-tag-key.ts
similarity index 98%
rename from packages/wonder-stuff-sentry/src/is-reserved-tag-key.js
rename to packages/wonder-stuff-sentry/src/is-reserved-tag-key.ts
index 8da90424..b0636fbd 100644
--- a/packages/wonder-stuff-sentry/src/is-reserved-tag-key.js
+++ b/packages/wonder-stuff-sentry/src/is-reserved-tag-key.ts
@@ -1,4 +1,3 @@
-// @flow
 import type {KindErrorDataOptions} from "./types";
 
 /**
diff --git a/packages/wonder-stuff-sentry/src/is-tag-key-valid.js b/packages/wonder-stuff-sentry/src/is-tag-key-valid.ts
similarity index 98%
rename from packages/wonder-stuff-sentry/src/is-tag-key-valid.js
rename to packages/wonder-stuff-sentry/src/is-tag-key-valid.ts
index 1cf76118..68d541b4 100644
--- a/packages/wonder-stuff-sentry/src/is-tag-key-valid.js
+++ b/packages/wonder-stuff-sentry/src/is-tag-key-valid.ts
@@ -1,5 +1,3 @@
-// @flow
-
 // Tag keys must be no more than 32 characters long.
 const MAX_TAG_KEY_LENGTH = 32;
 
diff --git a/packages/wonder-stuff-sentry/src/kind-error-data.js b/packages/wonder-stuff-sentry/src/kind-error-data.ts
similarity index 90%
rename from packages/wonder-stuff-sentry/src/kind-error-data.js
rename to packages/wonder-stuff-sentry/src/kind-error-data.ts
index 2c0a4ffb..d3ae660e 100644
--- a/packages/wonder-stuff-sentry/src/kind-error-data.js
+++ b/packages/wonder-stuff-sentry/src/kind-error-data.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors} from "@khanacademy/wonder-stuff-core";
 import type {
     SentryEvent,
@@ -14,18 +13,18 @@ import {DefaultKindErrorDataOptions} from "./default-kind-error-data-options";
 import {isTagKeyValid} from "./is-tag-key-valid";
 import {KindSentryError} from "./kind-sentry-error";
 
-type InvalidTags = {|
-    invalidKindTag?: string,
-    invalidGroupByTag?: string,
-    invalidConcatenatedMessageTag?: string,
-|};
+type InvalidTags = {
+    invalidKindTag?: string;
+    invalidGroupByTag?: string;
+    invalidConcatenatedMessageTag?: string;
+};
 
 export class KindErrorData implements SentryIntegration {
     static id: string = "KindErrorData";
     name: string = KindErrorData.id;
-    +_options: KindErrorDataOptions;
+    readonly _options: KindErrorDataOptions;
 
-    constructor(options: $Partial<KindErrorDataOptions> = Object.freeze({})) {
+    constructor(options: Partial<KindErrorDataOptions> = Object.freeze({})) {
         this._options = {
             ...DefaultKindErrorDataOptions,
             ...options,
@@ -73,6 +72,7 @@ export class KindErrorData implements SentryIntegration {
                 if (!self) {
                     return event;
                 }
+                // @ts-expect-error [FEI-5011] - TS2339 - Property 'enhanceEventWithErrorData' does not exist on type 'SentryIntegration'.
                 return self.enhanceEventWithErrorData(event, hint);
             },
         );
@@ -115,7 +115,7 @@ export class KindErrorData implements SentryIntegration {
         const updatedContexts = {
             ...event.contexts,
             ...contexts,
-        };
+        } as const;
         /**
          * NOTE: If you don't see Sentry serializing the right depth in your
          * contexts, increase the `normalizeDepth` option of the Sentry
diff --git a/packages/wonder-stuff-sentry/src/kind-sentry-error.js b/packages/wonder-stuff-sentry/src/kind-sentry-error.ts
similarity index 90%
rename from packages/wonder-stuff-sentry/src/kind-sentry-error.js
rename to packages/wonder-stuff-sentry/src/kind-sentry-error.ts
index a66f9391..adced220 100644
--- a/packages/wonder-stuff-sentry/src/kind-sentry-error.js
+++ b/packages/wonder-stuff-sentry/src/kind-sentry-error.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError, Errors} from "@khanacademy/wonder-stuff-core";
 import type {Metadata} from "@khanacademy/wonder-stuff-core";
 import type {SentryData} from "./types";
@@ -13,8 +12,7 @@ type Options = {
      *
      * @type {?Error}
      */
-    cause?: ?Error,
-
+    cause?: Error | null | undefined;
     /**
      * Sentry tags, contexts, and fingerprint information to be attached.
      *
@@ -22,8 +20,7 @@ type Options = {
      *
      * @type {?$Partial<SentryData>}
      */
-    sentryData?: ?$Partial<SentryData>,
-
+    sentryData?: Partial<SentryData> | null | undefined;
     /**
      * Other data to be attached to the error.
      *
@@ -31,42 +28,37 @@ type Options = {
      *
      * @type {?Metadata}
      */
-    metadata?: ?Metadata,
-
+    metadata?: Metadata | null | undefined;
     /**
      * A prefix to be added to the error name.
      *
      * @type {?string}
      */
-    prefix?: ?string,
-
+    prefix?: string | null | undefined;
     /**
      * A name for the error.
      *
      * @type {?string}
      */
-    name?: ?string,
-
+    name?: string | null | undefined;
     /**
      * The number of stack frames to strip from the error.
      *
      * @type {?number}
      */
-    stripStackFrames?: ?number,
-
+    stripStackFrames?: number | null | undefined;
     /**
      * The minimum number of stack frames to try and retain.
      *
      * @type {?number}
      */
-    minimumFrameCount?: ?number,
-
+    minimumFrameCount?: number | null | undefined;
     /**
      * Should we create a composite stack from the causal error chain or not?
      *
      * @type {?boolean}
      */
-    compositeStack?: ?boolean,
+    compositeStack?: boolean | null | undefined;
 };
 
 /**
@@ -161,14 +153,12 @@ export class KindSentryError extends KindError {
         });
     }
 
-    get sentryData(): $ReadOnly<SentryData> {
+    get sentryData(): Readonly<SentryData> {
         // (1) We always ensure there is metadata
         // (2) We know that the sentry data has the fields we need.
         // (3) We know that the sentry data in the metadata only has the fields
         //     we need.
-        // $FlowIgnore[incompatible-use] (1)
-        // $FlowIgnore[incompatible-return] (2)
-        // $FlowIgnore[incompatible-indexer] (3)
+        // @ts-expect-error [FEI-5011] - TS2322 - Type 'MetadataPrimitive | Metadata | MetadataArray<MetadataPrimitive | Metadata>' is not assignable to type 'Readonly<SentryData>'. | TS2533 - Object is possibly 'null' or 'undefined'.
         return this.metadata.sentry;
     }
 }
diff --git a/packages/wonder-stuff-sentry/src/normalize-sentry-data.js b/packages/wonder-stuff-sentry/src/normalize-sentry-data.ts
similarity index 89%
rename from packages/wonder-stuff-sentry/src/normalize-sentry-data.js
rename to packages/wonder-stuff-sentry/src/normalize-sentry-data.ts
index 61ec43a0..a5fad340 100644
--- a/packages/wonder-stuff-sentry/src/normalize-sentry-data.js
+++ b/packages/wonder-stuff-sentry/src/normalize-sentry-data.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors} from "@khanacademy/wonder-stuff-core";
 import {EmptySentryData} from "./empty-sentry-data";
 import {KindSentryError} from "./kind-sentry-error";
@@ -25,14 +24,22 @@ import {isReservedContextProperty} from "./is-reserved-context-property";
  */
 export function normalizeSentryData(
     options: KindErrorDataOptions,
-    data: ?$ReadOnly<$Partial<SentryData>>,
+    data?: Readonly<Partial<SentryData>> | null,
 ): SentryData {
     // https://docs.sentry.io/platforms/python/guides/logging/enriching-events/tags/
     const tags: SentryTags = {
         ...data?.tags,
     };
-    const invalidKeys = [];
-    const usedReservedKeys = [];
+    const invalidKeys: Array<
+        | MetadataPrimitive
+        | Metadata
+        | MetadataArray<MetadataPrimitive | Metadata>
+    > = [];
+    const usedReservedKeys: Array<
+        | MetadataPrimitive
+        | Metadata
+        | MetadataArray<MetadataPrimitive | Metadata>
+    > = [];
     // We want to valid tag keys and normalize tag values.
     // However, we don't bother with the validation production.
     for (const key of Object.keys(tags)) {
@@ -59,9 +66,9 @@ export function normalizeSentryData(
     // If the contexts contain any reserved property names, report them, but
     // only in production.
     if (process.env.NODE_ENV !== "production") {
-        const reservedPropertyContexts: {|
-            [string]: Array<string>,
-        |} = {};
+        const reservedPropertyContexts: {
+            [key: string]: Array<string>;
+        } = {};
         const contexts = data?.contexts;
         if (contexts != null) {
             for (const contextName of Object.keys(contexts)) {
@@ -97,7 +104,7 @@ export function normalizeSentryData(
                                 invalid_tag_keys: invalidKeys,
                                 reserved_tag_keys: usedReservedKeys,
                                 contexts_with_reserved_properties:
-                                    (reservedPropertyContexts: $FlowFixMe),
+                                    reservedPropertyContexts as any,
                             },
                         },
                     },
diff --git a/packages/wonder-stuff-sentry/src/sentry-data-reducer.js b/packages/wonder-stuff-sentry/src/sentry-data-reducer.ts
similarity index 91%
rename from packages/wonder-stuff-sentry/src/sentry-data-reducer.js
rename to packages/wonder-stuff-sentry/src/sentry-data-reducer.ts
index 9d24aaee..3668b12c 100644
--- a/packages/wonder-stuff-sentry/src/sentry-data-reducer.js
+++ b/packages/wonder-stuff-sentry/src/sentry-data-reducer.ts
@@ -1,4 +1,3 @@
-// @flow
 import {
     safeStringify,
     getOriginalStackFromError,
@@ -26,7 +25,7 @@ import {EmptySentryData} from "./empty-sentry-data";
  */
 export const sentryDataReducer = (
     options: KindErrorDataOptions,
-    accumulator: $ReadOnly<SentryData>,
+    accumulator: Readonly<SentryData>,
     current: Error,
     index: number,
 ): SentryData => {
@@ -49,11 +48,11 @@ export const sentryDataReducer = (
     // contexts, tags?
 
     // Combine tags by spreading the current tags over the accumulator tags.
-    const tags = {...accumulatorTags, ...currentTags};
+    const tags = {...accumulatorTags, ...currentTags} as const;
 
     // Combine contexts by spreading the current contexts over the accumulator
     // contexts.
-    const contexts = {...accumulatorContexts, ...currentContexts};
+    const contexts = {...accumulatorContexts, ...currentContexts} as const;
 
     // Combine fingerprint information, making sure to deduplicate via a Set and
     // remove any empty strings with a Boolean filter.
@@ -65,6 +64,7 @@ export const sentryDataReducer = (
 
     // Next, unless the index is 0, we need to add a context for the error.
     if (index !== 0) {
+        // @ts-expect-error [FEI-5011] - TS2542 - Index signature in type '{ readonly [x: string]: Metadata; }' only permits reading.
         contexts[
             `${causalErrorContextPrefix}${index}` // e.g., "Source Error - 1"
         ] = {
diff --git a/packages/wonder-stuff-sentry/src/truncate-tag-value.js b/packages/wonder-stuff-sentry/src/truncate-tag-value.ts
similarity index 98%
rename from packages/wonder-stuff-sentry/src/truncate-tag-value.js
rename to packages/wonder-stuff-sentry/src/truncate-tag-value.ts
index 27b05440..26dc76c5 100644
--- a/packages/wonder-stuff-sentry/src/truncate-tag-value.js
+++ b/packages/wonder-stuff-sentry/src/truncate-tag-value.ts
@@ -1,4 +1,3 @@
-// @flow
 import {truncateMiddle} from "@khanacademy/wonder-stuff-core";
 
 // Tag values must be no more than 200 characters long.
diff --git a/packages/wonder-stuff-sentry/src/types.js b/packages/wonder-stuff-sentry/src/types.ts
similarity index 76%
rename from packages/wonder-stuff-sentry/src/types.js
rename to packages/wonder-stuff-sentry/src/types.ts
index 34dcb9b7..dad74ec0 100644
--- a/packages/wonder-stuff-sentry/src/types.js
+++ b/packages/wonder-stuff-sentry/src/types.ts
@@ -1,4 +1,5 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2307 - Cannot find module 'flow-to-typescript-codemod' or its corresponding type declarations.
+import {Flow} from "flow-to-typescript-codemod";
 import type {Metadata} from "@khanacademy/wonder-stuff-core";
 
 /**
@@ -7,7 +8,7 @@ import type {Metadata} from "@khanacademy/wonder-stuff-core";
  * The key of each item is the name of the tag.
  */
 export type SentryTags = {
-    [name: string]: string,
+    [name: string]: string;
 };
 
 /**
@@ -23,7 +24,7 @@ export type SentryContext = Metadata;
  * The key of each item is the name of the context.
  */
 export type SentryContexts = {
-    [name: string]: SentryContext,
+    [name: string]: SentryContext;
 };
 
 /**
@@ -48,50 +49,45 @@ export type SentryFingerprint = Array<string>;
  * associated sentry event.
  * This is equivalent to using the `setFingerprint` API.
  */
-export type SentryData = {|
+export type SentryData = {
     /**
      * This is passed to setTags on the sentry scope.
      * Tags help categorize things.
      */
-    tags: SentryTags,
-
+    tags: SentryTags;
     /**
      * These are each passed to setContext on the sentry scope.
      * Contexts create a new headed section in the sentry report.
      * Useful for grouping specific context together.
      */
-    contexts: SentryContexts,
-
+    contexts: SentryContexts;
     /**
      * This is passed to setFingerprint on the sentry scope.
      * The fingerprint helps group like messages that otherwise would not
      * get grouped.
      */
-    fingerprint: SentryFingerprint,
-|};
+    fingerprint: SentryFingerprint;
+};
 
 export type KindErrorDataOptions = {
     /**
      * The name to use for the Sentry tag that indicates the error kind.
      */
-    +kindTagName: string,
-
+    readonly kindTagName: string;
     /**
      * The name to use for the Sentry tag that indicates the grouping string.
      */
-    +groupByTagName: string,
-
+    readonly groupByTagName: string;
     /**
      * The name to use for the Sentry tag that contains the concatenated error.
      */
-    +concatenatedMessageTagName: string,
-
+    readonly concatenatedMessageTagName: string;
     /**
      * The prefix to use for Sentry contexts that contain information about
      * each error in the causal error chain.
      * A unique number is appended to the prefix to create the context name.
      */
-    +causalErrorContextPrefix: string,
+    readonly causalErrorContextPrefix: string;
 
     // TODO(somewhatabstract): Allow configuration of which fields we include
     // in causal error contexts.
@@ -122,46 +118,49 @@ export interface SentryEvent {
     release?: string;
     dist?: string;
     environment?: string;
-    sdk?: $FlowFixMe;
+    sdk?: any;
     request?: Request;
     transaction?: string;
-    modules?: {[key: string]: string};
+    modules?: {
+        [key: string]: string;
+    };
     fingerprint?: SentryFingerprint;
     exception?: {
-        values?: Array<$FlowFixMe>,
+        values?: Array<any>;
     };
-    stacktrace?: $FlowFixMe;
-    breadcrumbs?: Array<$FlowFixMe>;
+    stacktrace?: any;
+    breadcrumbs?: Array<any>;
     contexts?: SentryContexts;
     tags?: SentryTags;
     extra?: SentryContext;
-    user?: $FlowFixMe;
-    type?: $FlowFixMe;
-    spans?: Array<$FlowFixMe>;
-    measurements?: $FlowFixMe;
-    debug_meta?: $FlowFixMe;
+    user?: any;
+    type?: any;
+    spans?: Array<any>;
+    measurements?: any;
+    debug_meta?: any;
 }
 
 export interface SentryEventHint {
     event_id?: string;
-    captureContext?: $FlowFixMe;
-    syntheticException?: ?Error;
-    originalException?: ?(Error | string);
-    data?: $FlowFixMe;
+    captureContext?: any;
+    syntheticException?: Error | null | undefined;
+    originalException?: Error | string | null | undefined;
+    data?: any;
 }
 
 export type SentryEventProcessor = (
     event: SentryEvent,
     hint?: SentryEventHint,
-) => Promise<?SentryEvent> | ?SentryEvent;
+) => Promise<SentryEvent | null | undefined> | SentryEvent | null | undefined;
 
 export interface SentryHub {
-    getIntegration<T: SentryIntegration>(integration: Class<T>): ?T;
+    getIntegration<T extends SentryIntegration>(
+        integration: Flow.Class<T>,
+    ): T | null | undefined;
 }
 
 export interface SentryIntegration {
     name: string;
-
     /**
      * Sets the integration up only once.
      * This takes no options on purpose, options should be passed in the constructor
diff --git a/packages/wonder-stuff-server-google/src/__tests__/__snapshots__/trace-impl.test.js.snap b/packages/wonder-stuff-server-google/src/__tests__/__snapshots__/trace-impl.test.ts.snap
similarity index 100%
rename from packages/wonder-stuff-server-google/src/__tests__/__snapshots__/trace-impl.test.js.snap
rename to packages/wonder-stuff-server-google/src/__tests__/__snapshots__/trace-impl.test.ts.snap
diff --git a/packages/wonder-stuff-server-google/src/__tests__/add-app-engine-middleware.test.js b/packages/wonder-stuff-server-google/src/__tests__/add-app-engine-middleware.test.ts
similarity index 74%
rename from packages/wonder-stuff-server-google/src/__tests__/add-app-engine-middleware.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/add-app-engine-middleware.test.ts
index f7f103cc..6db0a16f 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/add-app-engine-middleware.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/add-app-engine-middleware.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as Express from "express";
 import {Runtime} from "@khanacademy/wonder-stuff-server";
 import * as LoggingWinston from "@google-cloud/logging-winston";
@@ -11,11 +10,11 @@ jest.mock("@google-cloud/logging-winston");
 describe("#addAppEngineMiddleware", () => {
     it("should use the passed application", async () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendApp = ({}: $FlowFixMe);
-        const newApp = ({
+        const pretendLogger = {} as any;
+        const pretendApp = {} as any;
+        const newApp = {
             use: jest.fn().mockReturnThis(),
-        }: $FlowFixMe);
+        } as any;
         jest.spyOn(Express, "default").mockReturnValue(newApp);
 
         // Act
@@ -28,15 +27,16 @@ describe("#addAppEngineMiddleware", () => {
     describe("in production", () => {
         it("should add the logging-winston middleware", async () => {
             // Arrange
-            const pretendLogger = ({}: $FlowFixMe);
-            const pretendApp = ({}: $FlowFixMe);
-            const newApp = ({
+            const pretendLogger = {} as any;
+            const pretendApp = {} as any;
+            const newApp = {
                 use: jest.fn().mockReturnThis(),
-            }: $FlowFixMe);
+            } as any;
             jest.spyOn(Express, "default").mockReturnValue(newApp);
             jest.spyOn(
                 LoggingWinston.express,
                 "makeMiddleware",
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'Promise<(req: ServerRequest, res: ServerResponse<IncomingMessage>, next: Function) => void>'.
             ).mockReturnValue("FAKE_LW_EXPRESS");
 
             // Act
@@ -52,14 +52,15 @@ describe("#addAppEngineMiddleware", () => {
 
         it("should pass the logger to logging-winston middleware", async () => {
             // Arrange
-            const pretendLogger = ("FAKE_LOGGER": $FlowFixMe);
-            const pretendApp = ({}: $FlowFixMe);
-            const newApp = ({
+            const pretendLogger = "FAKE_LOGGER" as any;
+            const pretendApp = {} as any;
+            const newApp = {
                 use: jest.fn().mockReturnThis(),
-            }: $FlowFixMe);
+            } as any;
             jest.spyOn(Express, "default").mockReturnValue(newApp);
             const lwSpy = jest
                 .spyOn(LoggingWinston.express, "makeMiddleware")
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'Promise<(req: ServerRequest, res: ServerResponse<IncomingMessage>, next: Function) => void>'.
                 .mockReturnValue("FAKE_LW_EXPRESS");
 
             // Act
@@ -74,14 +75,14 @@ describe("#addAppEngineMiddleware", () => {
         });
     });
 
-    describe.each([Runtime.Test, Runtime.Development])("in %s", (mode) => {
+    describe.each([Runtime.Test, Runtime.Development])("in %s", (mode: any) => {
         it("should not add the logging-winston middleware", async () => {
             // Arrange
-            const pretendLogger = ({}: $FlowFixMe);
-            const pretendApp = ({}: $FlowFixMe);
-            const newApp = ({
+            const pretendLogger = {} as any;
+            const pretendApp = {} as any;
+            const newApp = {
                 use: jest.fn().mockReturnThis(),
-            }: $FlowFixMe);
+            } as any;
             jest.spyOn(Express, "default").mockReturnValue(newApp);
             const lwSpy = jest.spyOn(LoggingWinston.express, "makeMiddleware");
 
@@ -95,12 +96,12 @@ describe("#addAppEngineMiddleware", () => {
 
     it("should add requestID middleware", async () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendApp = ({}: $FlowFixMe);
-        const pretendMiddleware = ({}: $FlowFixMe);
-        const newApp = ({
+        const pretendLogger = {} as any;
+        const pretendApp = {} as any;
+        const pretendMiddleware = {} as any;
+        const newApp = {
             use: jest.fn().mockReturnThis(),
-        }: $FlowFixMe);
+        } as any;
         jest.spyOn(Express, "default").mockReturnValue(newApp);
         jest.spyOn(
             MakeAppEngineRequestIDMiddleware,
@@ -116,12 +117,12 @@ describe("#addAppEngineMiddleware", () => {
 
     it("should pass logger to requestID middleware", async () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendApp = ({}: $FlowFixMe);
-        const pretendMiddleware = ({}: $FlowFixMe);
-        const newApp = ({
+        const pretendLogger = {} as any;
+        const pretendApp = {} as any;
+        const pretendMiddleware = {} as any;
+        const newApp = {
             use: jest.fn().mockReturnThis(),
-        }: $FlowFixMe);
+        } as any;
         jest.spyOn(Express, "default").mockReturnValue(newApp);
         const makeMiddlewareSpy = jest
             .spyOn(
@@ -139,11 +140,11 @@ describe("#addAppEngineMiddleware", () => {
 
     it("should return the updated application", async () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendApp = ({}: $FlowFixMe);
-        const newApp = ({
+        const pretendLogger = {} as any;
+        const pretendApp = {} as any;
+        const newApp = {
             use: jest.fn().mockReturnThis(),
-        }: $FlowFixMe);
+        } as any;
         jest.spyOn(Express, "default").mockReturnValue(newApp);
 
         // Act
diff --git a/packages/wonder-stuff-server-google/src/__tests__/get-app-engine-info.test.js b/packages/wonder-stuff-server-google/src/__tests__/get-app-engine-info.test.ts
similarity index 96%
rename from packages/wonder-stuff-server-google/src/__tests__/get-app-engine-info.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/get-app-engine-info.test.ts
index 701a45f9..23070956 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/get-app-engine-info.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/get-app-engine-info.test.ts
@@ -1,7 +1,6 @@
-// @flow
 import {getAppEngineInfo} from "../get-app-engine-info";
 
-const resetEnv = (name: string, value: ?string): void => {
+const resetEnv = (name: string, value?: string | null): void => {
     if (value == null) {
         delete process.env[name];
     } else {
diff --git a/packages/wonder-stuff-server-google/src/__tests__/get-appengine-request-id.test.js b/packages/wonder-stuff-server-google/src/__tests__/get-appengine-request-id.test.ts
similarity index 83%
rename from packages/wonder-stuff-server-google/src/__tests__/get-appengine-request-id.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/get-appengine-request-id.test.ts
index bf1cbc97..9d857fb5 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/get-appengine-request-id.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/get-appengine-request-id.test.ts
@@ -1,12 +1,11 @@
-// @flow
 import {getAppEngineRequestID} from "../get-app-engine-request-id";
 
 describe("#getAppEngineRequestID", () => {
     it("should return null when header is absent", () => {
         // Arrange
-        const request = ({
+        const request = {
             header: jest.fn(),
-        }: $FlowFixMe);
+        } as any;
 
         // Act
         const result = getAppEngineRequestID(request);
@@ -17,13 +16,13 @@ describe("#getAppEngineRequestID", () => {
 
     it("should return the requestID when it does not end with 000101xx", () => {
         // Arrange
-        const request = ({
-            header: jest.fn((key) =>
+        const request = {
+            header: jest.fn((key: any) =>
                 key === "X-Appengine-Request-Log-Id"
                     ? "this-is-a-good-request-id"
                     : null,
             ),
-        }: $FlowFixMe);
+        } as any;
 
         // Act
         const result = getAppEngineRequestID(request);
@@ -34,13 +33,13 @@ describe("#getAppEngineRequestID", () => {
 
     it("should return a fixed requestID when it does end with 000101xx", () => {
         // Arrange
-        const request = ({
-            header: jest.fn((key) =>
+        const request = {
+            header: jest.fn((key: any) =>
                 key === "X-Appengine-Request-Log-Id"
                     ? "this-is-a-bad-request-id-000101BD"
                     : null,
             ),
-        }: $FlowFixMe);
+        } as any;
 
         // Act
         const result = getAppEngineRequestID(request);
diff --git a/packages/wonder-stuff-server-google/src/__tests__/get-delta.test.js b/packages/wonder-stuff-server-google/src/__tests__/get-delta.test.ts
similarity index 66%
rename from packages/wonder-stuff-server-google/src/__tests__/get-delta.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/get-delta.test.ts
index b6507246..c24f7e41 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/get-delta.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/get-delta.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {getDelta} from "../get-delta";
 
 describe("#getDelta", () => {
@@ -8,14 +7,15 @@ describe("#getDelta", () => {
             a: 30,
             b: 0,
             c: 40000,
-        };
+        } as const;
         const second = {
             a: 60,
             b: 30,
             c: 10000,
-        };
+        } as const;
 
         // Act
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly a: 60; readonly b: 30; readonly c: 10000; }' is not assignable to parameter of type '{ readonly a: 30; readonly b: 0; readonly c: 40000; }'.
         const result = getDelta(first, second);
 
         // Assert
diff --git a/packages/wonder-stuff-server-google/src/__tests__/setup-integrations.test.js b/packages/wonder-stuff-server-google/src/__tests__/setup-integrations.test.ts
similarity index 72%
rename from packages/wonder-stuff-server-google/src/__tests__/setup-integrations.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/setup-integrations.test.ts
index 2f66aafe..eae63860 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/setup-integrations.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/setup-integrations.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as DebugAgent from "@google-cloud/debug-agent";
 import * as Profiler from "@google-cloud/profiler";
 import {Runtime} from "@khanacademy/wonder-stuff-server";
@@ -59,27 +58,30 @@ describe("#setupIntegrations", () => {
         });
     });
 
-    describe.each([Runtime.Test, Runtime.Development])("in %s", (runtime) => {
-        it("should not setup @google-cloud/debug-agent", async () => {
-            // Arrange
-            const agentSpy = jest.spyOn(DebugAgent, "start");
+    describe.each([Runtime.Test, Runtime.Development])(
+        "in %s",
+        (runtime: any) => {
+            it("should not setup @google-cloud/debug-agent", async () => {
+                // Arrange
+                const agentSpy = jest.spyOn(DebugAgent, "start");
 
-            // Act
-            await setupIntegrations(runtime);
+                // Act
+                await setupIntegrations(runtime);
 
-            // Assert
-            expect(agentSpy).not.toHaveBeenCalled();
-        });
+                // Assert
+                expect(agentSpy).not.toHaveBeenCalled();
+            });
 
-        it("should not setup @google-cloud/profiler", async () => {
-            // Arrange
-            const agentSpy = jest.spyOn(Profiler, "start");
+            it("should not setup @google-cloud/profiler", async () => {
+                // Arrange
+                const agentSpy = jest.spyOn(Profiler, "start");
 
-            // Act
-            await setupIntegrations(runtime);
+                // Act
+                await setupIntegrations(runtime);
 
-            // Assert
-            expect(agentSpy).not.toHaveBeenCalled();
-        });
-    });
+                // Assert
+                expect(agentSpy).not.toHaveBeenCalled();
+            });
+        },
+    );
 });
diff --git a/packages/wonder-stuff-server-google/src/__tests__/start-server.test.js b/packages/wonder-stuff-server-google/src/__tests__/start-server.test.ts
similarity index 86%
rename from packages/wonder-stuff-server-google/src/__tests__/start-server.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/start-server.test.ts
index a69cebff..0e31f274 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/start-server.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/start-server.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as Server from "@khanacademy/wonder-stuff-server";
 import * as LoggingWinston from "@google-cloud/logging-winston";
 import * as AddAppEngineMiddleware from "../add-app-engine-middleware";
@@ -13,6 +12,7 @@ jest.mock("@google-cloud/logging-winston");
 
 describe("#start-server", () => {
     beforeEach(() => {
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '() => void' is not assignable to parameter of type '(event: string | symbol, listener: (...args: any[]) => void) => Process'.
         jest.spyOn(process, "on").mockImplementation(() => {});
     });
 
@@ -35,8 +35,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             mode: Server.Runtime.Test,
             logLevel: "debug",
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         jest.spyOn(
             AddAppEngineMiddleware,
             "addAppEngineMiddleware",
@@ -59,8 +59,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logLevel: "debug",
             mode: Server.Runtime.Test,
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         jest.spyOn(
             AddAppEngineMiddleware,
             "addAppEngineMiddleware",
@@ -86,8 +86,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logLevel: "debug",
             mode: Server.Runtime.Test,
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         jest.spyOn(
             AddAppEngineMiddleware,
             "addAppEngineMiddleware",
@@ -118,8 +118,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logLevel: "debug",
             mode: Server.Runtime.Test,
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         jest.spyOn(
             AddAppEngineMiddleware,
             "addAppEngineMiddleware",
@@ -128,6 +128,7 @@ describe("#start-server", () => {
             GetDefaultLogMetadata,
             "getDefaultLogMetadata",
         ).mockReturnValue({
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ here: string; }' is not assignable to parameter of type '{ instanceID: string; processID: number; }'.
             here: "is default metadata",
         });
 
@@ -157,8 +158,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logLevel: "debug",
             mode: Server.Runtime.Production,
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         jest.spyOn(
             AddAppEngineMiddleware,
             "addAppEngineMiddleware",
@@ -167,10 +168,12 @@ describe("#start-server", () => {
             GetDefaultLogMetadata,
             "getDefaultLogMetadata",
         ).mockReturnValue({
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ here: string; }' is not assignable to parameter of type '{ instanceID: string; processID: number; }'.
             here: "is default metadata",
         });
         jest.spyOn(LoggingWinston, "LoggingWinston").mockImplementation(
-            ({level}) => ({
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '({ level, }: any) => { wut: string; }' is not assignable to parameter of type '(options?: Options | undefined) => LoggingWinston'.
+            ({level}: any) => ({
                 wut: `FAKE_${level}_LW_TRANSPORT`,
             }),
         );
@@ -201,8 +204,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logLevel: "debug",
             mode: Server.Runtime.Test,
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         const addAppEngineMiddlewareSpy = jest
             .spyOn(AddAppEngineMiddleware, "addAppEngineMiddleware")
             .mockResolvedValue(pretendApp);
@@ -230,8 +233,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logLevel: "debug",
             mode: Server.Runtime.Test,
-        };
-        const pretendApp = ({}: $FlowFixMe);
+        } as const;
+        const pretendApp = {} as any;
         jest.spyOn(
             AddAppEngineMiddleware,
             "addAppEngineMiddleware",
diff --git a/packages/wonder-stuff-server-google/src/__tests__/trace-impl.test.js b/packages/wonder-stuff-server-google/src/__tests__/trace-impl.test.ts
similarity index 73%
rename from packages/wonder-stuff-server-google/src/__tests__/trace-impl.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/trace-impl.test.ts
index cc8900ee..32d12c35 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/trace-impl.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/trace-impl.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as GetAppEngineInfo from "../get-app-engine-info";
 import {traceImpl} from "../trace-impl";
 
@@ -7,9 +6,10 @@ jest.mock("../get-app-engine-info");
 describe("#trace", () => {
     it.each([[""], [null], [undefined]])(
         "should throw if the action is empty/falsy",
-        (testPoint) => {
+        (testPoint: any) => {
             // Arrange
-            const fakeLogger = ({}: $FlowFixMe);
+            const fakeLogger = {} as any;
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
             jest.spyOn(GetAppEngineInfo, "getAppEngineInfo").mockReturnValue({
                 name: "GATEWAY_NAME",
                 version: "GATEWAY_VERSION",
@@ -25,10 +25,11 @@ describe("#trace", () => {
 
     it("should log the start of the session", () => {
         // Arrange
-        const fakeLogger = ({
+        const fakeLogger = {
             silly: jest.fn(),
             startTimer: jest.fn(),
-        }: $FlowFixMe);
+        } as any;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
         jest.spyOn(GetAppEngineInfo, "getAppEngineInfo").mockReturnValue({
             name: "GATEWAY_NAME",
             version: "GATEWAY_VERSION",
@@ -43,10 +44,11 @@ describe("#trace", () => {
 
     it("should start a timer", () => {
         // Arrange
-        const fakeLogger = ({
+        const fakeLogger = {
             silly: jest.fn(),
             startTimer: jest.fn(),
-        }: $FlowFixMe);
+        } as any;
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
         jest.spyOn(GetAppEngineInfo, "getAppEngineInfo").mockReturnValue({
             name: "GATEWAY_NAME",
             version: "GATEWAY_VERSION",
@@ -61,13 +63,14 @@ describe("#trace", () => {
 
     it("should create a tracer span", () => {
         // Arrange
-        const fakeLogger: $FlowFixMe = {
+        const fakeLogger: any = {
             silly: jest.fn(),
             startTimer: jest.fn(),
         };
-        const fakeTracer: $FlowFixMe = {
+        const fakeTracer: any = {
             createChildSpan: jest.fn(),
         };
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
         jest.spyOn(GetAppEngineInfo, "getAppEngineInfo").mockReturnValue({
             name: "GATEWAY_NAME",
             version: "GATEWAY_VERSION",
@@ -84,10 +87,11 @@ describe("#trace", () => {
 
     it("should return a trace session", () => {
         // Arrange
-        const fakeLogger: $FlowFixMe = {
+        const fakeLogger: any = {
             silly: jest.fn(),
             startTimer: jest.fn(),
         };
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
         jest.spyOn(GetAppEngineInfo, "getAppEngineInfo").mockReturnValue({
             name: "GATEWAY_NAME",
             version: "GATEWAY_VERSION",
@@ -104,13 +108,14 @@ describe("#trace", () => {
         describe("#action", () => {
             it("should give action of the trace", () => {
                 // Arrange
-                const fakeLogger: $FlowFixMe = {
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn(),
                 };
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -126,13 +131,14 @@ describe("#trace", () => {
 
             it("should be read-only", () => {
                 // Arrange
-                const fakeLogger: $FlowFixMe = {
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn(),
                 };
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -140,13 +146,7 @@ describe("#trace", () => {
                 const session = traceImpl(fakeLogger, "ACTION", "MESSAGE");
 
                 // Act
-                /**
-                 * $FlowExpectedError[cannot-write] Flow is going to complain
-                 * because name is readonly.
-                 * We will suppress this because we want to test that runtime
-                 * code is enforcing this. The idea of this test is to ensure
-                 * that folks don't edit out this specific behavior.
-                 */
+                // @ts-expect-error [FEI-5011] - TS2322 - Type 'string' is not assignable to type '() => string'.
                 const underTest = () => (session.action = "NEW_ACTION!");
 
                 // Assert
@@ -165,21 +165,24 @@ describe("#trace", () => {
                 // Arrange
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(process, "memoryUsage")
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 10000,
                     })
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 50000,
                     });
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -206,21 +209,24 @@ describe("#trace", () => {
                 // Arrange
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(process, "memoryUsage")
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 10000,
                     })
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 50000,
                     });
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -247,21 +253,24 @@ describe("#trace", () => {
                 // Arrange
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(process, "memoryUsage")
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 10000,
                     })
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 50000,
                     });
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -292,21 +301,24 @@ describe("#trace", () => {
                 // Arrange
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(process, "memoryUsage")
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 50000,
                     })
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 10000,
                     });
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -340,21 +352,24 @@ describe("#trace", () => {
                 // Arrange
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(process, "memoryUsage")
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 10000,
                     })
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 50000,
                     });
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -391,21 +406,24 @@ describe("#trace", () => {
                 // Arrange
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(process, "memoryUsage")
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 10000,
                     })
                     .mockReturnValueOnce({
+                        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ someMemoryStuff: number; }' is not assignable to parameter of type 'MemoryUsage'.
                         someMemoryStuff: 50000,
                     });
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
@@ -435,20 +453,21 @@ describe("#trace", () => {
                 const fakeTraceSpan = {
                     addLabel: jest.fn(),
                     endSpan: jest.fn(),
-                };
-                const fakeTracer: $FlowFixMe = {
+                } as const;
+                const fakeTracer: any = {
                     createChildSpan: jest.fn().mockReturnValue(fakeTraceSpan),
                 };
                 const fakeTimer = {
                     done: jest.fn(),
-                };
-                const fakeLogger: $FlowFixMe = {
+                } as const;
+                const fakeLogger: any = {
                     silly: jest.fn(),
                     startTimer: jest.fn().mockReturnValue(fakeTimer),
                 };
                 jest.spyOn(
                     GetAppEngineInfo,
                     "getAppEngineInfo",
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ name: string; version: string; }' is not assignable to parameter of type 'AppEngineInfo'.
                 ).mockReturnValue({
                     name: "GATEWAY_NAME",
                     version: "GATEWAY_VERSION",
diff --git a/packages/wonder-stuff-server-google/src/__tests__/trace.test.js b/packages/wonder-stuff-server-google/src/__tests__/trace.test.ts
similarity index 76%
rename from packages/wonder-stuff-server-google/src/__tests__/trace.test.js
rename to packages/wonder-stuff-server-google/src/__tests__/trace.test.ts
index b2947560..fe105a5a 100644
--- a/packages/wonder-stuff-server-google/src/__tests__/trace.test.js
+++ b/packages/wonder-stuff-server-google/src/__tests__/trace.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as TraceAgent from "@google-cloud/trace-agent";
 import * as Server from "@khanacademy/wonder-stuff-server";
 import * as TraceImpl from "../trace-impl";
@@ -12,11 +11,11 @@ describe("#trace", () => {
     describe("with request", () => {
         it("should pass request to getLogger", () => {
             // Arrange
-            const fakeRequest: $FlowFixMe = ({
+            const fakeRequest: any = {
                 url: "",
-            }: $FlowFixMe);
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            } as any;
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             const getLoggerSpy = jest
                 .spyOn(Server, "getLogger")
@@ -31,11 +30,11 @@ describe("#trace", () => {
 
         it("should invoke the shared trace implementation with the logger and tracer", () => {
             // Arrange
-            const fakeRequest: $FlowFixMe = ({
+            const fakeRequest: any = {
                 url: "",
-            }: $FlowFixMe);
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            } as any;
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             jest.spyOn(Server, "getLogger").mockReturnValue(fakeLogger);
             const traceImplSpy = jest.spyOn(TraceImpl, "traceImpl");
@@ -54,12 +53,12 @@ describe("#trace", () => {
 
         it("should return the trace session", () => {
             // Arrange
-            const fakeTraceSession: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeRequest: $FlowFixMe = ({
+            const fakeTraceSession: any = {} as any;
+            const fakeRequest: any = {
                 url: "",
-            }: $FlowFixMe);
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            } as any;
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             jest.spyOn(Server, "getLogger").mockReturnValue(fakeLogger);
             jest.spyOn(TraceImpl, "traceImpl").mockReturnValue(
@@ -77,8 +76,8 @@ describe("#trace", () => {
     describe("without logger nor request", () => {
         it("should invoke the shared trace implementation with the logger and tracer", () => {
             // Arrange
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             jest.spyOn(Server, "getLogger").mockReturnValue(fakeLogger);
             const traceImplSpy = jest.spyOn(TraceImpl, "traceImpl");
@@ -97,9 +96,9 @@ describe("#trace", () => {
 
         it("should return the trace session", () => {
             // Arrange
-            const fakeTraceSession: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            const fakeTraceSession: any = {} as any;
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             jest.spyOn(Server, "getLogger").mockReturnValue(fakeLogger);
             jest.spyOn(TraceImpl, "traceImpl").mockReturnValue(
@@ -117,8 +116,8 @@ describe("#trace", () => {
     describe("with logger", () => {
         it("should invoke the shared trace implementation with the logger and tracer", () => {
             // Arrange
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             const traceImplSpy = jest.spyOn(TraceImpl, "traceImpl");
 
@@ -136,9 +135,9 @@ describe("#trace", () => {
 
         it("should return the trace session", () => {
             // Arrange
-            const fakeTraceSession: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeLogger: $FlowFixMe = ({}: $FlowFixMe);
-            const fakeTracer: $FlowFixMe = ({}: $FlowFixMe);
+            const fakeTraceSession: any = {} as any;
+            const fakeLogger: any = {} as any;
+            const fakeTracer: any = {} as any;
             jest.spyOn(TraceAgent, "get").mockReturnValue(fakeTracer);
             jest.spyOn(TraceImpl, "traceImpl").mockReturnValue(
                 fakeTraceSession,
diff --git a/packages/wonder-stuff-server-google/src/add-app-engine-middleware.js b/packages/wonder-stuff-server-google/src/add-app-engine-middleware.ts
similarity index 63%
rename from packages/wonder-stuff-server-google/src/add-app-engine-middleware.js
rename to packages/wonder-stuff-server-google/src/add-app-engine-middleware.ts
index 83047b68..1103d842 100644
--- a/packages/wonder-stuff-server-google/src/add-app-engine-middleware.js
+++ b/packages/wonder-stuff-server-google/src/add-app-engine-middleware.ts
@@ -1,6 +1,5 @@
-// @flow
 import express from "express";
-import type {$Application, $Request, $Response} from "express";
+import type {Application, Request, Response} from "express";
 import {Runtime} from "@khanacademy/wonder-stuff-server";
 import type {Logger} from "@khanacademy/wonder-stuff-server";
 import * as lw from "@google-cloud/logging-winston";
@@ -9,11 +8,17 @@ import {makeAppEngineRequestIDMiddleware} from "./middleware/make-app-engine-req
 /**
  * Apply the middleware that we want to use with Google App Engine (GAE).
  */
-export async function addAppEngineMiddleware<TReq: $Request, TRes: $Response>(
-    app: $Application<TReq, TRes>,
-    mode: $Values<typeof Runtime>,
+export async function addAppEngineMiddleware<
+    TReq extends Request,
+    TRes extends Response,
+>(
+    // @ts-expect-error [FEI-5011] - TS2315 - Type 'Application' is not generic.
+    app: Application<TReq, TRes>,
+    mode: (typeof Runtime)[keyof typeof Runtime],
     logger: Logger,
-): Promise<$Application<TReq, TRes>> {
+    // @ts-expect-error [FEI-5011] - TS2315 - Type 'Application' is not generic.
+): Promise<Application<TReq, TRes>> {
+    // @ts-expect-error [FEI-5011] - TS2558 - Expected 0 type arguments, but got 2.
     const middlewareApp = express<TReq, TRes>();
 
     /**
diff --git a/packages/wonder-stuff-server-google/src/get-app-engine-info.js b/packages/wonder-stuff-server-google/src/get-app-engine-info.ts
similarity index 98%
rename from packages/wonder-stuff-server-google/src/get-app-engine-info.js
rename to packages/wonder-stuff-server-google/src/get-app-engine-info.ts
index 23a63ed9..44975798 100644
--- a/packages/wonder-stuff-server-google/src/get-app-engine-info.js
+++ b/packages/wonder-stuff-server-google/src/get-app-engine-info.ts
@@ -1,4 +1,3 @@
-// @flow
 import type {AppEngineInfo} from "./types";
 
 /**
diff --git a/packages/wonder-stuff-server-google/src/get-app-engine-request-id.js b/packages/wonder-stuff-server-google/src/get-app-engine-request-id.ts
similarity index 87%
rename from packages/wonder-stuff-server-google/src/get-app-engine-request-id.js
rename to packages/wonder-stuff-server-google/src/get-app-engine-request-id.ts
index b71b860b..64fbae6d 100644
--- a/packages/wonder-stuff-server-google/src/get-app-engine-request-id.js
+++ b/packages/wonder-stuff-server-google/src/get-app-engine-request-id.ts
@@ -1,10 +1,11 @@
-// @flow
-import type {$Request} from "express";
+import type {Request} from "express";
 
 /**
  * Get the GAE request ID for a given request if it exists.
  */
-export const getAppEngineRequestID = (req: $Request): ?string => {
+export const getAppEngineRequestID = (
+    req: Request,
+): string | null | undefined => {
     const requestID = req.header("X-Appengine-Request-Log-Id");
     if (requestID == null) {
         return null;
diff --git a/packages/wonder-stuff-server-google/src/get-default-log-metadata.js b/packages/wonder-stuff-server-google/src/get-default-log-metadata.ts
similarity index 79%
rename from packages/wonder-stuff-server-google/src/get-default-log-metadata.js
rename to packages/wonder-stuff-server-google/src/get-default-log-metadata.ts
index 86b3887d..37195b10 100644
--- a/packages/wonder-stuff-server-google/src/get-default-log-metadata.js
+++ b/packages/wonder-stuff-server-google/src/get-default-log-metadata.ts
@@ -1,4 +1,3 @@
-// @flow
 import type {AppEngineInfo} from "./types";
 import {getAppEngineInfo} from "./get-app-engine-info";
 
@@ -6,8 +5,8 @@ import {getAppEngineInfo} from "./get-app-engine-info";
  * Get the default log metadata for a Google Cloud app engine server.
  */
 export const getDefaultLogMetadata = (): {
-    instanceID: AppEngineInfo["instance"],
-    processID: AppEngineInfo["pid"],
+    instanceID: AppEngineInfo["instance"];
+    processID: AppEngineInfo["pid"];
 } => {
     const {instance, pid} = getAppEngineInfo();
     return {
diff --git a/packages/wonder-stuff-server-google/src/get-delta.js b/packages/wonder-stuff-server-google/src/get-delta.js
deleted file mode 100644
index 218d3aa3..00000000
--- a/packages/wonder-stuff-server-google/src/get-delta.js
+++ /dev/null
@@ -1,13 +0,0 @@
-// @flow
-type NumberObj = {
-    [key: string]: number,
-    ...
-};
-
-export const getDelta = <T: NumberObj>(first: T, second: T): T => {
-    const result: $Shape<T> = {};
-    for (const key of Object.keys(first)) {
-        result[key] = second[key] - first[key];
-    }
-    return result;
-};
diff --git a/packages/wonder-stuff-server-google/src/get-delta.ts b/packages/wonder-stuff-server-google/src/get-delta.ts
new file mode 100644
index 00000000..3dea2613
--- /dev/null
+++ b/packages/wonder-stuff-server-google/src/get-delta.ts
@@ -0,0 +1,13 @@
+type NumberObj = {
+    [key: string]: number;
+};
+
+export const getDelta = <T extends NumberObj>(first: T, second: T): T => {
+    const result: Partial<T> = {};
+    for (const key of Object.keys(first)) {
+        // @ts-expect-error [FEI-5011] - TS2536 - Type 'string' cannot be used to index type 'Partial<T>'.
+        result[key] = second[key] - first[key];
+    }
+    // @ts-expect-error [FEI-5011] - TS2322 - Type 'Partial<T>' is not assignable to type 'T'.
+    return result;
+};
diff --git a/packages/wonder-stuff-server-google/src/index.js b/packages/wonder-stuff-server-google/src/index.ts
similarity index 92%
rename from packages/wonder-stuff-server-google/src/index.js
rename to packages/wonder-stuff-server-google/src/index.ts
index b535101d..ab5227f5 100644
--- a/packages/wonder-stuff-server-google/src/index.js
+++ b/packages/wonder-stuff-server-google/src/index.ts
@@ -1,3 +1,2 @@
-// @flow
 export {startServer} from "./start-server";
 export type {ServerOptions, GoogleCloudIntegrations} from "./types";
diff --git a/packages/wonder-stuff-server-google/src/middleware/__tests__/make-app-engine-request-id-middleware.test.js b/packages/wonder-stuff-server-google/src/middleware/__tests__/make-app-engine-request-id-middleware.test.ts
similarity index 65%
rename from packages/wonder-stuff-server-google/src/middleware/__tests__/make-app-engine-request-id-middleware.test.js
rename to packages/wonder-stuff-server-google/src/middleware/__tests__/make-app-engine-request-id-middleware.test.ts
index e469a01c..4601b130 100644
--- a/packages/wonder-stuff-server-google/src/middleware/__tests__/make-app-engine-request-id-middleware.test.js
+++ b/packages/wonder-stuff-server-google/src/middleware/__tests__/make-app-engine-request-id-middleware.test.ts
@@ -1,4 +1,3 @@
-//@flow
 import * as Server from "@khanacademy/wonder-stuff-server";
 import {makeAppEngineRequestIDMiddleware} from "../make-app-engine-request-id-middleware";
 import * as GetAppEngineRequestID from "../../get-app-engine-request-id";
@@ -8,12 +7,13 @@ jest.mock("../../get-app-engine-request-id");
 describe("#makeAppEngineRequestIDMiddleware", () => {
     it("should return middleware function", () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
+        const pretendLogger = {} as any;
 
         // Act
         const result = makeAppEngineRequestIDMiddleware(pretendLogger);
 
         // Assert
+        // @ts-expect-error [FEI-5011] - TS2339 - Property 'toBeFunction' does not exist on type 'JestMatchers<Middleware<TReq, TRes>>'.
         expect(result).toBeFunction();
     });
 
@@ -28,9 +28,9 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should not call getRequestLogger", () => {
                 // Arrange
-                const pretendDefaultLogger = ({}: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                const pretendDefaultLogger = {} as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
@@ -40,10 +40,6 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
                 );
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
@@ -52,9 +48,9 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should not create child logger from logger", () => {
                 // Arrange
-                const pretendDefaultLogger = ({child: jest.fn()}: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                const pretendDefaultLogger = {child: jest.fn()} as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
@@ -63,10 +59,6 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
                 );
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
@@ -75,18 +67,14 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should invoke next", () => {
                 // Arrange
-                const pretendDefaultLogger = ({}: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                const pretendDefaultLogger = {} as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
@@ -104,9 +92,9 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should use default logger and request with getRequestLogger to get logger", () => {
                 // Arrange
-                const pretendDefaultLogger = ({child: jest.fn()}: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                const pretendDefaultLogger = {child: jest.fn()} as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
@@ -115,10 +103,6 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
                     .mockReturnValue(pretendDefaultLogger);
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
@@ -130,9 +114,9 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should create child logger from logger with requestID", () => {
                 // Arrange
-                const pretendDefaultLogger = ({child: jest.fn()}: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                const pretendDefaultLogger = {child: jest.fn()} as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
@@ -141,10 +125,6 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
                 );
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
@@ -155,12 +135,12 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should attach child logger to request.log", () => {
                 // Arrange
-                const pretendChildLogger = ({}: $FlowFixMe);
-                const pretendDefaultLogger = ({
+                const pretendChildLogger = {} as any;
+                const pretendDefaultLogger = {
                     child: () => pretendChildLogger,
-                }: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                } as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
@@ -169,10 +149,6 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
                 );
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
@@ -181,9 +157,9 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
 
             it("should invoke next", () => {
                 // Arrange
-                const pretendDefaultLogger = ({child: jest.fn()}: $FlowFixMe);
-                const pretendRequest = ({}: $FlowFixMe);
-                const pretendResponse = ({}: $FlowFixMe);
+                const pretendDefaultLogger = {child: jest.fn()} as any;
+                const pretendRequest = {} as any;
+                const pretendResponse = {} as any;
                 const mockNext = jest.fn();
                 const middleware =
                     makeAppEngineRequestIDMiddleware(pretendDefaultLogger);
@@ -192,10 +168,6 @@ describe("#makeAppEngineRequestIDMiddleware", () => {
                 );
 
                 // Act
-                /**
-                 * $FlowIgnore[incompatible-call] The return type of Middleware
-                 * can be error or non-error middleware and this confuses flow.
-                 */
                 middleware(pretendRequest, pretendResponse, mockNext);
 
                 // Assert
diff --git a/packages/wonder-stuff-server-google/src/middleware/make-app-engine-request-id-middleware.js b/packages/wonder-stuff-server-google/src/middleware/make-app-engine-request-id-middleware.ts
similarity index 80%
rename from packages/wonder-stuff-server-google/src/middleware/make-app-engine-request-id-middleware.js
rename to packages/wonder-stuff-server-google/src/middleware/make-app-engine-request-id-middleware.ts
index a755036d..2362dbb9 100644
--- a/packages/wonder-stuff-server-google/src/middleware/make-app-engine-request-id-middleware.js
+++ b/packages/wonder-stuff-server-google/src/middleware/make-app-engine-request-id-middleware.ts
@@ -1,5 +1,5 @@
-// @flow
-import type {$Response, $Request, Middleware, NextFunction} from "express";
+// @ts-expect-error [FEI-5011] - TS2305 - Module '"express"' has no exported member 'Middleware'.
+import type {Response, Request, Middleware, NextFunction} from "express";
 import {getRequestLogger} from "@khanacademy/wonder-stuff-server";
 import type {Logger, RequestWithLog} from "@khanacademy/wonder-stuff-server";
 import {getAppEngineRequestID} from "../get-app-engine-request-id";
@@ -9,10 +9,10 @@ import {getAppEngineRequestID} from "../get-app-engine-request-id";
  * that will attach the GAE requestID to the log metadata.
  */
 export function makeAppEngineRequestIDMiddleware<
-    TReq: RequestWithLog<$Request>,
-    TRes: $Response,
+    TReq extends RequestWithLog<Request>,
+    TRes extends Response,
 >(defaultLogger: Logger): Middleware<TReq, TRes> {
-    return <TReq: RequestWithLog<$Request>, TRes: $Response>(
+    return <TReq extends RequestWithLog<Request>, TRes extends Response>(
         req: TReq,
         res: TRes,
         next: NextFunction,
diff --git a/packages/wonder-stuff-server-google/src/setup-integrations.js b/packages/wonder-stuff-server-google/src/setup-integrations.ts
similarity index 94%
rename from packages/wonder-stuff-server-google/src/setup-integrations.js
rename to packages/wonder-stuff-server-google/src/setup-integrations.ts
index 470b19d9..1889d69d 100644
--- a/packages/wonder-stuff-server-google/src/setup-integrations.js
+++ b/packages/wonder-stuff-server-google/src/setup-integrations.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Runtime} from "@khanacademy/wonder-stuff-server";
 import type {GoogleCloudIntegrations} from "./types";
 
@@ -8,7 +7,7 @@ import type {GoogleCloudIntegrations} from "./types";
  * These integrations help debug production services.
  */
 export const setupIntegrations = async (
-    mode: $Values<typeof Runtime>,
+    mode: (typeof Runtime)[keyof typeof Runtime],
     {debugAgent, profiler}: GoogleCloudIntegrations = {
         debugAgent: false,
         profiler: false,
diff --git a/packages/wonder-stuff-server-google/src/start-server.js b/packages/wonder-stuff-server-google/src/start-server.ts
similarity index 86%
rename from packages/wonder-stuff-server-google/src/start-server.js
rename to packages/wonder-stuff-server-google/src/start-server.ts
index afd8dfe0..0f555ca9 100644
--- a/packages/wonder-stuff-server-google/src/start-server.js
+++ b/packages/wonder-stuff-server-google/src/start-server.ts
@@ -1,5 +1,4 @@
-// @flow
-import type {$Application, $Request, $Response} from "express";
+import type {Application, Request, Response} from "express";
 import {
     startServer as startServerCore,
     Runtime,
@@ -20,12 +19,12 @@ import {getDefaultLogMetadata} from "./get-default-log-metadata";
  * middleware before listening on the appropriate port per the passed options.
  */
 export async function startServer<
-    TReq: RequestWithLog<$Request>,
-    TRes: $Response,
+    TReq extends RequestWithLog<Request>,
+    TRes extends Response,
 >(
     options: ServerOptions,
-    app: $Application<TReq, TRes>,
-): Promise<?http$Server> {
+    app: Application<TReq, TRes>,
+): Promise<http.Server | null | undefined> {
     const {integrations, logLevel, ...restOptions} = options;
 
     /**
@@ -47,6 +46,7 @@ export async function startServer<
             // In production, we use the Google Cloud logging winston transport.
             restOptions.mode === Runtime.Production
                 ? new lw.LoggingWinston({
+                      // @ts-expect-error [FEI-5011] - TS2322 - Type 'string | number | symbol' is not assignable to type 'string | undefined'.
                       level: logLevel,
                   })
                 : null,
diff --git a/packages/wonder-stuff-server-google/src/trace-impl.js b/packages/wonder-stuff-server-google/src/trace-impl.ts
similarity index 92%
rename from packages/wonder-stuff-server-google/src/trace-impl.js
rename to packages/wonder-stuff-server-google/src/trace-impl.ts
index 15234b41..8fbbc024 100644
--- a/packages/wonder-stuff-server-google/src/trace-impl.js
+++ b/packages/wonder-stuff-server-google/src/trace-impl.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2305 - Module '"@google-cloud/trace-agent"' has no exported member 'Tracer'.
 import type {Tracer} from "@google-cloud/trace-agent";
 import {Errors, KindError} from "@khanacademy/wonder-stuff-core";
 import type {Logger} from "@khanacademy/wonder-stuff-server";
@@ -75,9 +75,9 @@ export const traceImpl = (
      */
     const span = tracer?.createChildSpan({name: `${gatewayName}.${action}`});
 
-    const profileLabels: {|
-        [string]: mixed,
-    |} = {};
+    const profileLabels: {
+        [key: string]: unknown;
+    } = {};
     const addLabel = <T>(name: string, value: T): void => {
         /**
          * Track this so we can also include it in our logging info.
@@ -107,7 +107,7 @@ export const traceImpl = (
          * and so `getDelta` isn't typed to handle that. Have to rethink
          * how to make that work.
          */
-        // $FlowFixMe[incompatible-call]
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'MemoryUsage' is not assignable to parameter of type 'NumberObj'.
         addLabel("/memory/delta", getDelta(beforeMemory, afterMemory));
         addLabel("/memory/final", afterMemory);
 
@@ -119,7 +119,6 @@ export const traceImpl = (
          * We suppress flow because we want the TraceSessionInfo to overwrite
          * things and it's OK if we don't know what things it overwrites.
          */
-        // $FlowIgnore[cannot-spread-indexer]
         const metadata = {
             /**
              * We have to add the default metadata because winston does not
@@ -130,7 +129,7 @@ export const traceImpl = (
             ...profileLabels,
             ...info,
             message: `TRACED ${logMessage}`,
-        };
+        } as const;
 
         /**
          * Let's mark our profile as done.
@@ -150,6 +149,7 @@ export const traceImpl = (
     };
 
     return {
+        // @ts-expect-error [FEI-5011] - TS2322 - Type 'string' is not assignable to type '() => string'.
         get action() {
             return action;
         },
diff --git a/packages/wonder-stuff-server-google/src/trace.js b/packages/wonder-stuff-server-google/src/trace.ts
similarity index 89%
rename from packages/wonder-stuff-server-google/src/trace.js
rename to packages/wonder-stuff-server-google/src/trace.ts
index 7b6689ba..d37fec52 100644
--- a/packages/wonder-stuff-server-google/src/trace.js
+++ b/packages/wonder-stuff-server-google/src/trace.ts
@@ -1,7 +1,6 @@
-// @flow
 import * as traceAgent from "@google-cloud/trace-agent";
 import {getLogger} from "@khanacademy/wonder-stuff-server";
-import type {$Request} from "express";
+import type {Request} from "express";
 import type {Logger, RequestWithLog} from "@khanacademy/wonder-stuff-server";
 import {traceImpl} from "./trace-impl";
 import type {ITraceSession} from "./types";
@@ -25,12 +24,11 @@ interface ITrace {
      * @returns {ITraceSession} The new trace session that was created and is to be
      * used to end the session.
      */
-    <TReq: RequestWithLog<$Request>>(
+    <TReq extends RequestWithLog<Request>>(
         action: string,
         message: string,
         request?: TReq,
     ): ITraceSession;
-
     /**
      * Start tracing an event.
      *
@@ -57,7 +55,7 @@ interface ITrace {
 export const trace: ITrace = (
     action: string,
     message: string,
-    requestOrLogger: mixed,
+    requestOrLogger: unknown,
 ): ITraceSession => {
     const tracer = traceAgent.get();
     if (
@@ -67,12 +65,11 @@ export const trace: ITrace = (
     ) {
         // We have done a little check to make sure this is either null
         // or a request, so just tell Flow it's OK.
-        // $FlowIgnore[incompatible-call]
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'unknown' is not assignable to parameter of type 'RequestWithLog<Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>> | undefined'.
         const logger = getLogger(requestOrLogger);
         return traceImpl(logger, action, message, tracer);
     }
 
     // At this point, we can assume it's a logger.
-    // $FlowIgnore[incompatible-call]
     return traceImpl(requestOrLogger, action, message, tracer);
 };
diff --git a/packages/wonder-stuff-server-google/src/types.js b/packages/wonder-stuff-server-google/src/types.ts
similarity index 83%
rename from packages/wonder-stuff-server-google/src/types.js
rename to packages/wonder-stuff-server-google/src/types.ts
index 49bd9a48..632518ab 100644
--- a/packages/wonder-stuff-server-google/src/types.js
+++ b/packages/wonder-stuff-server-google/src/types.ts
@@ -1,4 +1,3 @@
-// @flow
 import type {
     LogLevel,
     ServerOptions as BaseServerOptions,
@@ -12,13 +11,12 @@ export type GoogleCloudIntegrations = {
      * Enable the debug agent.
      * Defaults to false.
      */
-    +debugAgent?: boolean,
-
+    readonly debugAgent?: boolean;
     /**
      * Enable the profiler.
      * Defaults to false.
      */
-    +profiler?: boolean,
+    readonly profiler?: boolean;
 };
 
 /**
@@ -28,22 +26,19 @@ export type AppEngineInfo = {
     /**
      * Usually the value of GAE_SERVICE, if set. Otherwise, "unknown".
      */
-    +name: string,
-
+    readonly name: string;
     /**
      * Usually the value of GAE_VERSION, if set. Otherwise, "unknown".
      */
-    +version: string,
-
+    readonly version: string;
     /**
      * Usually the value of GAE_INSTANCE, if set. Otherwise, "unknown".
      */
-    +instance: string,
-
+    readonly instance: string;
     /**
      * The process identifier.
      */
-    +pid: number,
+    readonly pid: number;
 };
 
 /**
@@ -53,34 +48,28 @@ export type ServerOptions = {
     /**
      * Configuration for various Google Cloud agents that can aid debugging.
      */
-    +integrations?: GoogleCloudIntegrations,
-
+    readonly integrations?: GoogleCloudIntegrations;
     /**
      * The name of the server.
      */
-    +name: BaseServerOptions["name"],
-
+    readonly name: BaseServerOptions["name"];
     /**
      * The port on which the server should listen.
      */
-    +port: BaseServerOptions["port"],
-
+    readonly port: BaseServerOptions["port"];
     /**
      * The hostname to which the server should bind.
      */
-    +host: BaseServerOptions["host"],
-
+    readonly host: BaseServerOptions["host"];
     /**
      * What runtime mode the server is running under.
      */
-    +mode: BaseServerOptions["mode"],
-
+    readonly mode: BaseServerOptions["mode"];
     /**
      * The log level at which to log things. Anything at or more serious than
      * this level will be logged.
      */
-    +logLevel: LogLevel,
-
+    readonly logLevel: LogLevel;
     /**
      * Optional value in milliseconds for keepalive timeout of the server.
      * For running in Google Cloud, this should be higher than the load
@@ -91,8 +80,7 @@ export type ServerOptions = {
      *
      * Defaults to 90000.
      */
-    +keepAliveTimeout?: BaseServerOptions["keepAliveTimeout"],
-
+    readonly keepAliveTimeout?: BaseServerOptions["keepAliveTimeout"];
     /**
      * When `true`, the "heapdump" package will be loaded, allowing for
      * heap dumps to be generated on demand using `kill -USR2 <pid>` where
@@ -101,7 +89,7 @@ export type ServerOptions = {
      * Defaults to `false` in production mode, and `true` in all other modes.
      * Set explicitly to `false` to disable heap dumps in all modes.
      */
-    +allowHeapDumps?: BaseServerOptions["allowHeapDumps"],
+    readonly allowHeapDumps?: BaseServerOptions["allowHeapDumps"];
 };
 
 /**
@@ -111,13 +99,12 @@ export type TraceSessionInfo = {
     /**
      * The level at which to log the session.
      */
-    +level?: LogLevel,
-
+    readonly level?: LogLevel;
     /**
      * Additional metadata about the session. Unlike using `addLabel` on the
      * trace session, this will only go to logging and not the trace as well.
      */
-    +[datum: string]: mixed,
+    readonly [datum: string]: unknown;
 };
 
 /**
@@ -127,8 +114,7 @@ export interface ITraceSession {
     /**
      * The name of the action being traced as provided when it was started.
      */
-    get action(): string;
-
+    action(): string;
     /**
      * Add a label to the trace session.
      *
@@ -138,7 +124,6 @@ export interface ITraceSession {
      * string in tracing if it isn't one already.
      */
     addLabel<T>(name: string, value: T): void;
-
     /**
      * End the trace session.
      *
diff --git a/packages/wonder-stuff-server/src/__tests__/__snapshots__/get-logging-transport.test.js.snap b/packages/wonder-stuff-server/src/__tests__/__snapshots__/get-logging-transport.test.ts.snap
similarity index 100%
rename from packages/wonder-stuff-server/src/__tests__/__snapshots__/get-logging-transport.test.js.snap
rename to packages/wonder-stuff-server/src/__tests__/__snapshots__/get-logging-transport.test.ts.snap
diff --git a/packages/wonder-stuff-server/src/__tests__/create-logger.test.js b/packages/wonder-stuff-server/src/__tests__/create-logger.test.ts
similarity index 72%
rename from packages/wonder-stuff-server/src/__tests__/create-logger.test.js
rename to packages/wonder-stuff-server/src/__tests__/create-logger.test.ts
index bcd229b3..94c11dc7 100644
--- a/packages/wonder-stuff-server/src/__tests__/create-logger.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/create-logger.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import winston from "winston";
 import {Errors} from "@khanacademy/wonder-stuff-core";
 import * as GetLoggingTransport from "../get-logging-transport";
@@ -12,6 +11,7 @@ import {Runtime} from "../types";
 describe("#createLogger", () => {
     beforeEach(() => {
         // We silence winston's console output.
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ debug: jest.Mock<any, any, any>; }' is not assignable to parameter of type 'Logger'.
         jest.spyOn(winston, "createLogger").mockReturnValue({
             debug: jest.fn(),
         });
@@ -28,7 +28,7 @@ describe("#createLogger", () => {
 
         // Assert
         expect(getLoggingTransportMock).toHaveBeenCalledWith(
-            (Runtime.Test: string),
+            Runtime.Test as string,
             "debug",
         );
     });
@@ -54,6 +54,7 @@ describe("#createLogger", () => {
     it("should log creation parameters to created logger", () => {
         // Arrange
         const debugSpy = jest.fn();
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ debug: jest.Mock<any, any, any>; }' is not assignable to parameter of type 'Logger'.
         jest.spyOn(winston, "createLogger").mockReturnValue({
             debug: debugSpy,
         });
@@ -78,6 +79,7 @@ describe("#createLogger", () => {
 
         // Act
         createLogger({mode: Runtime.Test, level: "info"});
+        // @ts-expect-error [FEI-5011] - TS2532 - Object is possibly 'undefined'.
         const result = createLoggerMock.mock.calls[0][0].format;
 
         // Assert
@@ -88,11 +90,11 @@ describe("#createLogger", () => {
         it("should set the error kind when logging an error that has no kind", () => {
             // Arrange
             const winstonFormatSpy = jest.spyOn(winston, "format");
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'splat' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.splat = jest.fn();
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'printf' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.printf = jest.fn();
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'combine' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.combine = jest.fn();
             createLogger({mode: Runtime.Test, level: "info"});
             const formatFn = winstonFormatSpy.mock.calls[0][0];
@@ -110,11 +112,11 @@ describe("#createLogger", () => {
         it("should not set the error kind when logging an error that has a kind already set", () => {
             // Arrange
             const winstonFormatSpy = jest.spyOn(winston, "format");
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'splat' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.splat = jest.fn();
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'printf' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.printf = jest.fn();
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'combine' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.combine = jest.fn();
             createLogger({mode: Runtime.Test, level: "info"});
             const formatFn = winstonFormatSpy.mock.calls[0][0];
@@ -133,11 +135,11 @@ describe("#createLogger", () => {
         it("should not set the kind when the level of the message is not error", () => {
             // Arrange
             const winstonFormatSpy = jest.spyOn(winston, "format");
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'splat' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.splat = jest.fn();
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'printf' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.printf = jest.fn();
-            // $FlowIgnore[prop-missing]
+            // @ts-expect-error [FEI-5011] - TS2339 - Property 'combine' does not exist on type 'SpyInstance<FormatWrap, [transform: TransformFunction], any>'.
             winstonFormatSpy.combine = jest.fn();
             createLogger({mode: Runtime.Test, level: "info"});
             const formatFn = winstonFormatSpy.mock.calls[0][0];
diff --git a/packages/wonder-stuff-server/src/__tests__/get-agent-for-url.test.js b/packages/wonder-stuff-server/src/__tests__/get-agent-for-url.test.ts
similarity index 99%
rename from packages/wonder-stuff-server/src/__tests__/get-agent-for-url.test.js
rename to packages/wonder-stuff-server/src/__tests__/get-agent-for-url.test.ts
index f302c906..fa59ab10 100644
--- a/packages/wonder-stuff-server/src/__tests__/get-agent-for-url.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/get-agent-for-url.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {URL} from "url";
 
 describe("#getAgentForURL", () => {
diff --git a/packages/wonder-stuff-server/src/__tests__/get-logger.test.js b/packages/wonder-stuff-server/src/__tests__/get-logger.test.ts
similarity index 67%
rename from packages/wonder-stuff-server/src/__tests__/get-logger.test.js
rename to packages/wonder-stuff-server/src/__tests__/get-logger.test.ts
index f84ff21b..a5f2cfd7 100644
--- a/packages/wonder-stuff-server/src/__tests__/get-logger.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/get-logger.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as RootLogger from "../root-logger";
 import {getLogger} from "../get-logger";
 
@@ -13,7 +12,7 @@ describe("get-logger.js", () => {
     describe("#getLogger", () => {
         it("should return the root logger when there is no request", async () => {
             // Arrange
-            const fakeLogger = {};
+            const fakeLogger: Record<string, any> = {};
             jest.spyOn(RootLogger, "getRootLogger").mockReturnValue(fakeLogger);
 
             // Act
@@ -25,11 +24,11 @@ describe("get-logger.js", () => {
 
         it("should return the root logger when the request has no log", async () => {
             // Arrange
-            const fakeLogger = {};
+            const fakeLogger: Record<string, any> = {};
             jest.spyOn(RootLogger, "getRootLogger").mockReturnValue(fakeLogger);
 
             // Act
-            // $FlowIgnore[incompatible-call]
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{}' is not assignable to parameter of type 'RequestWithLog<Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>>'.
             const result = getLogger({});
 
             // Assert
@@ -38,16 +37,15 @@ describe("get-logger.js", () => {
 
         it("should return the request logger when the request has a log", async () => {
             // Arrange
-            const fakeLogger = {};
+            const fakeLogger: Record<string, any> = {};
             jest.spyOn(RootLogger, "getRootLogger").mockReturnValue(fakeLogger);
-            const pretendRequestLogger = {};
+            const pretendRequestLogger: Record<string, any> = {};
             const pretendRequest = {
                 log: pretendRequestLogger,
-            };
+            } as const;
 
             // Act
-            // $FlowIgnore[prop-missing]
-            // $FlowIgnore[incompatible-call]
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '{ readonly log: Record<string, any>; }' is not assignable to parameter of type 'RequestWithLog<Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>>'.
             const result = getLogger(pretendRequest);
 
             // Assert
diff --git a/packages/wonder-stuff-server/src/__tests__/get-logging-transport.test.js b/packages/wonder-stuff-server/src/__tests__/get-logging-transport.test.ts
similarity index 74%
rename from packages/wonder-stuff-server/src/__tests__/get-logging-transport.test.js
rename to packages/wonder-stuff-server/src/__tests__/get-logging-transport.test.ts
index 4800350d..b8c8c8fa 100644
--- a/packages/wonder-stuff-server/src/__tests__/get-logging-transport.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/get-logging-transport.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import winston from "winston";
 // TODO(somewhatabstract, FEI-4174): Update eslint-plugin-import when they
 // have fixed:
@@ -23,9 +22,11 @@ describe("#getLoggingTransport", () => {
         it("should format log messages to include metadata", () => {
             // Arrange
             const fakePrintF = jest.fn();
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'. | TS2339 - Property 'mockReturnValue' does not exist on type 'never'.
             jest.spyOn(winston.format, "combine", "get").mockReturnValue(
                 jest.fn(),
             );
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'. | TS2339 - Property 'mockReturnValue' does not exist on type 'never'.
             jest.spyOn(winston.format, "printf", "get").mockReturnValue(
                 fakePrintF,
             );
@@ -52,7 +53,7 @@ describe("#getLoggingTransport", () => {
             // Arrange
 
             // Act
-            // $FlowIgnore[incompatible-call]
+            // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '"MADE UP RUNTIME MODE"' is not assignable to parameter of type '"production" | "test" | "development"'.
             const result = getLoggingTransport("MADE UP RUNTIME MODE", "silly");
 
             // Assert
@@ -73,12 +74,14 @@ describe("#getLoggingTransport", () => {
 
         it.each([undefined, {other: "metadata"}, {}])(
             "should format log messages to include metadata when present (%s)",
-            (otherMetadata) => {
+            (otherMetadata: any) => {
                 // Arrange
                 const fakePrintF = jest.fn();
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'. | TS2339 - Property 'mockReturnValue' does not exist on type 'never'.
                 jest.spyOn(winston.format, "combine", "get").mockReturnValue(
                     jest.fn(),
                 );
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'. | TS2339 - Property 'mockReturnValue' does not exist on type 'never'.
                 jest.spyOn(winston.format, "printf", "get").mockReturnValue(
                     fakePrintF,
                 );
@@ -110,13 +113,15 @@ describe("#getLoggingTransport", () => {
 
         it.each([undefined, {other: "metadata"}, {}])(
             "should format log messages to include metadata when present (%s)",
-            (otherMetadata) => {
+            (otherMetadata: any) => {
                 // Arrange
                 jest.spyOn(winston, "createLogger");
                 const fakePrintF = jest.fn();
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'. | TS2339 - Property 'mockReturnValue' does not exist on type 'never'.
                 jest.spyOn(winston.format, "combine", "get").mockReturnValue(
                     jest.fn(),
                 );
+                // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'string' is not assignable to parameter of type 'never'. | TS2339 - Property 'mockReturnValue' does not exist on type 'never'.
                 jest.spyOn(winston.format, "printf", "get").mockReturnValue(
                     fakePrintF,
                 );
diff --git a/packages/wonder-stuff-server/src/__tests__/get-request-logger.test.js b/packages/wonder-stuff-server/src/__tests__/get-request-logger.test.ts
similarity index 77%
rename from packages/wonder-stuff-server/src/__tests__/get-request-logger.test.js
rename to packages/wonder-stuff-server/src/__tests__/get-request-logger.test.ts
index 72a24d6a..0eb7ec4e 100644
--- a/packages/wonder-stuff-server/src/__tests__/get-request-logger.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/get-request-logger.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {getRequestLogger} from "../get-request-logger";
 
 describe("#getRequestLogger", () => {
@@ -18,7 +17,7 @@ describe("#getRequestLogger", () => {
         // Arrange
 
         // Act
-        const underTest = () => getRequestLogger(null, ({}: $FlowFixMe));
+        const underTest = () => getRequestLogger(null, {} as any);
 
         // Assert
         expect(underTest).toThrowErrorMatchingInlineSnapshot(
@@ -28,7 +27,7 @@ describe("#getRequestLogger", () => {
 
     it("should return the default logger when there is no request", () => {
         // Arrange
-        const pretendDefaultLogger = ({}: $FlowFixMe);
+        const pretendDefaultLogger = {} as any;
 
         // Act
         const result = getRequestLogger(pretendDefaultLogger);
@@ -39,10 +38,10 @@ describe("#getRequestLogger", () => {
 
     it("should return the default logger when the request has no log", () => {
         // Arrange
-        const pretendDefaultLogger = ({}: $FlowFixMe);
+        const pretendDefaultLogger = {} as any;
 
         // Act
-        const result = getRequestLogger(pretendDefaultLogger, ({}: $FlowFixMe));
+        const result = getRequestLogger(pretendDefaultLogger, {} as any);
 
         // Assert
         expect(result).toBe(pretendDefaultLogger);
@@ -50,12 +49,12 @@ describe("#getRequestLogger", () => {
 
     it.each([{}, null])(
         "should return the request logger when the request has a log",
-        (defaultLogger) => {
+        (defaultLogger: any) => {
             // Arrange
-            const pretendRequestLogger = ({}: $FlowFixMe);
-            const pretendRequest = ({
+            const pretendRequestLogger = {} as any;
+            const pretendRequest = {
                 log: pretendRequestLogger,
-            }: $FlowFixMe);
+            } as any;
 
             // Act
             const result = getRequestLogger(defaultLogger, pretendRequest);
diff --git a/packages/wonder-stuff-server/src/__tests__/get-runtime-mode.test.js b/packages/wonder-stuff-server/src/__tests__/get-runtime-mode.test.ts
similarity index 76%
rename from packages/wonder-stuff-server/src/__tests__/get-runtime-mode.test.js
rename to packages/wonder-stuff-server/src/__tests__/get-runtime-mode.test.ts
index 99878a0c..31d12245 100644
--- a/packages/wonder-stuff-server/src/__tests__/get-runtime-mode.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/get-runtime-mode.test.ts
@@ -1,4 +1,3 @@
-// @flow
 // TODO(somewhatabstract, FEI-4174): Update eslint-plugin-import when they
 // have fixed:
 // https://github.com/import-js/eslint-plugin-import/issues/2073
@@ -19,7 +18,7 @@ describe("#getRuntimeMode", () => {
         [Runtime.Development, "dev"],
         [Runtime.Development, "development"],
         [Runtime.Test, "test"],
-    ])("should return %s for given %s", (expectation, nodeEnv) => {
+    ])("should return %s for given %s", (expectation: any, nodeEnv: any) => {
         // Arrange
         process.env.NODE_ENV = nodeEnv;
 
@@ -35,16 +34,19 @@ describe("#getRuntimeMode", () => {
         [Runtime.Development, undefined],
         [Runtime.Production, "blah"],
         [Runtime.Development, "blah"],
-    ])("should return %s if NODE_ENV unrecognised", (expectation, nodeEnv) => {
-        // Arrange
-        process.env.NODE_ENV = nodeEnv;
+    ])(
+        "should return %s if NODE_ENV unrecognised",
+        (expectation: any, nodeEnv: any) => {
+            // Arrange
+            process.env.NODE_ENV = nodeEnv;
 
-        // Act
-        const result = getRuntimeMode(expectation);
+            // Act
+            const result = getRuntimeMode(expectation);
 
-        // Assert
-        expect(result).toBe(expectation);
-    });
+            // Assert
+            expect(result).toBe(expectation);
+        },
+    );
 
     it.each([
         [Runtime.Development, "development"],
@@ -53,7 +55,7 @@ describe("#getRuntimeMode", () => {
         [Runtime.Production, "test"],
     ])(
         "should ignore default of %s and give precedent to NODE_ENV=%s",
-        (defaultValue, nodeEnv) => {
+        (defaultValue: any, nodeEnv: any) => {
             // Arrange
             process.env.NODE_ENV = nodeEnv;
 
diff --git a/packages/wonder-stuff-server/src/__tests__/root-logger.test.js b/packages/wonder-stuff-server/src/__tests__/root-logger.test.ts
similarity index 84%
rename from packages/wonder-stuff-server/src/__tests__/root-logger.test.js
rename to packages/wonder-stuff-server/src/__tests__/root-logger.test.ts
index 34c746b3..7f623ce0 100644
--- a/packages/wonder-stuff-server/src/__tests__/root-logger.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/root-logger.test.ts
@@ -1,4 +1,3 @@
-// @flow
 describe("root-logger.js", () => {
     beforeEach(() => {
         jest.resetModules();
@@ -8,10 +7,10 @@ describe("root-logger.js", () => {
         it("should throw if called more than once", () => {
             // Arrange
             const {setRootLogger} = require("../root-logger");
-            setRootLogger(({}: $FlowFixMe));
+            setRootLogger({} as any);
 
             // Act
-            const underTest = () => setRootLogger(({}: $FlowFixMe));
+            const underTest = () => setRootLogger({} as any);
 
             // Assert
             expect(underTest).toThrowErrorMatchingInlineSnapshot(
@@ -23,7 +22,7 @@ describe("root-logger.js", () => {
     describe("#getRootLogger", () => {
         it("should return the value passed to setRootLogger", () => {
             // Arrange
-            const fakeLogger: $FlowFixMe = {};
+            const fakeLogger: any = {};
             const {getRootLogger, setRootLogger} = require("../root-logger");
             setRootLogger(fakeLogger);
 
diff --git a/packages/wonder-stuff-server/src/__tests__/start-server.test.js b/packages/wonder-stuff-server/src/__tests__/start-server.test.ts
similarity index 87%
rename from packages/wonder-stuff-server/src/__tests__/start-server.test.js
rename to packages/wonder-stuff-server/src/__tests__/start-server.test.ts
index 91d908d8..f52164d1 100644
--- a/packages/wonder-stuff-server/src/__tests__/start-server.test.js
+++ b/packages/wonder-stuff-server/src/__tests__/start-server.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as Express from "express";
 import * as RootLogger from "../root-logger";
 import * as DefaultRequestLogging from "../middleware/default-request-logging";
@@ -19,12 +18,13 @@ jest.mock("../middleware/default-request-logging");
 
 describe("#start-server", () => {
     beforeEach(() => {
+        // @ts-expect-error [FEI-5011] - TS2345 - Argument of type '() => void' is not assignable to parameter of type '(event: string | symbol, listener: (...args: any[]) => void) => Process'.
         jest.spyOn(process, "on").mockImplementation(() => {});
     });
 
     it("should set the root logger to the given logger", async () => {
         // Arrange
-        const logger: $FlowFixMe = {
+        const logger: any = {
             debug: jest.fn(),
         };
         const options = {
@@ -33,8 +33,8 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logger,
             mode: Runtime.Test,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn(),
             use: jest.fn().mockReturnThis(),
         };
@@ -50,9 +50,9 @@ describe("#start-server", () => {
 
     it.each(Array.from(Object.values(Runtime)))(
         "should import heapdumps if allowHeapDumps is true",
-        async (mode) => {
+        async (mode: any) => {
             // Arrange
-            const logger: $FlowFixMe = {
+            const logger: any = {
                 debug: jest.fn(),
             };
             const options = {
@@ -62,13 +62,13 @@ describe("#start-server", () => {
                 logger,
                 mode,
                 allowHeapDumps: true,
-            };
+            } as const;
             const fakeServer = {
                 address: jest.fn(),
                 on: jest.fn(),
                 keepAliveTimeout: 0,
-            };
-            const pretendApp: $FlowFixMe = {
+            } as const;
+            const pretendApp: any = {
                 listen: jest.fn().mockReturnValue(fakeServer),
                 use: jest.fn().mockReturnThis(),
             };
@@ -88,7 +88,7 @@ describe("#start-server", () => {
 
     it("should import heapdumps if not production", async () => {
         // Arrange
-        const logger: $FlowFixMe = {
+        const logger: any = {
             debug: jest.fn(),
         };
         const options = {
@@ -97,13 +97,13 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logger,
             mode: Runtime.Development,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
             keepAliveTimeout: 0,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -122,7 +122,7 @@ describe("#start-server", () => {
 
     it("should not import heapdumps if in production", async () => {
         // Arrange
-        const logger: $FlowFixMe = {
+        const logger: any = {
             debug: jest.fn(),
         };
         const options = {
@@ -131,13 +131,13 @@ describe("#start-server", () => {
             host: "127.0.0.1",
             logger,
             mode: Runtime.Production,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
             keepAliveTimeout: 0,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -152,7 +152,7 @@ describe("#start-server", () => {
 
     it("should not import heapdumps if explicitly told not to", async () => {
         // Arrange
-        const logger: $FlowFixMe = {
+        const logger: any = {
             debug: jest.fn(),
         };
         const options = {
@@ -162,13 +162,13 @@ describe("#start-server", () => {
             logger,
             mode: Runtime.Development,
             allowHeapDumps: false,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
             keepAliveTimeout: 0,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -187,16 +187,16 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -219,17 +219,17 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
             includeRequestMiddleware: false,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -254,16 +254,16 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -285,17 +285,17 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
             includeErrorMiddleware: false,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -319,12 +319,12 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn(),
             use: jest.fn().mockReturnThis(),
         };
@@ -347,20 +347,20 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
-        };
+        } as const;
         const fakeServer = {
             address: () => ({
                 address: "ADDRESS",
                 port: "PORT",
             }),
             on: jest.fn(),
-        };
+        } as const;
         const listenMock = jest.fn().mockReturnValue(fakeServer);
-        const pretendApp: $FlowFixMe = {
+        const pretendApp: any = {
             listen: listenMock,
             use: jest.fn().mockReturnThis(),
         };
@@ -382,30 +382,30 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
-        };
-        let connectionHandler;
+        } as const;
+        let connectionHandler: any;
         const fakeServer = {
             address: () => ({
                 address: "ADDRESS",
                 port: "PORT",
             }),
-            on: jest.fn().mockImplementation((event, fn) => {
+            on: jest.fn().mockImplementation((event: any, fn: any) => {
                 if (event === "connection") {
                     connectionHandler = fn;
                 }
             }),
-        };
+        } as const;
         const fakeConnection = {
             remoteAddress: "CONNECTION_ADDRESS",
             remotePort: "CONNECTION_PORT",
             on: jest.fn(),
-        };
+        } as const;
         const listenMock = jest.fn().mockReturnValue(fakeServer);
-        const pretendApp: $FlowFixMe = {
+        const pretendApp: any = {
             listen: listenMock,
             use: jest.fn().mockReturnThis(),
         };
@@ -428,18 +428,18 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
             keepAliveTimeout: 42,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
             keepAliveTimeout: 0,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -459,17 +459,17 @@ describe("#start-server", () => {
             name: "TEST_GATEWAY",
             port: 42,
             host: "127.0.0.1",
-            logger: ({
+            logger: {
                 debug: jest.fn(),
-            }: $FlowFixMe),
+            } as any,
             mode: Runtime.Test,
-        };
+        } as const;
         const fakeServer = {
             address: jest.fn(),
             on: jest.fn(),
             keepAliveTimeout: 0,
-        };
-        const pretendApp: $FlowFixMe = {
+        } as const;
+        const pretendApp: any = {
             listen: jest.fn().mockReturnValue(fakeServer),
             use: jest.fn().mockReturnThis(),
         };
@@ -489,25 +489,25 @@ describe("#start-server", () => {
         ${42}            | ${5042}
     `(
         "should set headersTimeout to $headersTimeout when keepAliveTimeout is $keepAliveTimeout",
-        async ({keepAliveTimeout, headersTimeout}) => {
+        async ({keepAliveTimeout, headersTimeout}: any) => {
             // Arrange
             const options = {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     debug: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
                 keepAliveTimeout,
-            };
+            } as const;
             const fakeServer = {
                 address: jest.fn(),
                 on: jest.fn(),
                 keepAliveTimeout: 0,
                 headersTimeout: 0,
-            };
-            const pretendApp: $FlowFixMe = {
+            } as const;
+            const pretendApp: any = {
                 listen: jest.fn().mockReturnValue(fakeServer),
                 use: jest.fn().mockReturnThis(),
             };
@@ -529,14 +529,14 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     debug: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(null);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -561,13 +561,13 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(null);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -588,23 +588,23 @@ describe("#start-server", () => {
 
         it.each([[null, undefined, "ADDRESS"]])(
             "should report start failure if address is %s",
-            async (address) => {
+            async (address: any) => {
                 // Arrange
                 const options = {
                     name: "TEST_GATEWAY",
                     port: 42,
                     host: "127.0.0.1",
-                    logger: ({
+                    logger: {
                         warn: jest.fn(),
-                    }: $FlowFixMe),
+                    } as any,
                     mode: Runtime.Test,
-                };
+                } as const;
                 const fakeServer = {
                     address: () => address,
                     on: jest.fn(),
-                };
+                } as const;
                 const listenMock = jest.fn().mockReturnValue(fakeServer);
-                const pretendApp: $FlowFixMe = {
+                const pretendApp: any = {
                     listen: listenMock,
                     use: jest.fn().mockReturnThis(),
                 };
@@ -629,20 +629,20 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
                     port: "PORT",
                 }),
                 on: jest.fn(),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -668,13 +668,13 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(null);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -697,11 +697,11 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
@@ -709,9 +709,9 @@ describe("#start-server", () => {
                 }),
                 on: jest.fn(),
                 close: jest.fn(),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -737,12 +737,12 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
@@ -750,9 +750,9 @@ describe("#start-server", () => {
                 }),
                 on: jest.fn(),
                 close: jest.fn(),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -760,6 +760,7 @@ describe("#start-server", () => {
             const processOnSpy = jest.spyOn(process, "on");
             const processExitSpy = jest
                 .spyOn(process, "exit")
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 .mockReturnValue();
             await startServer(options, pretendApp);
             const errorSpy = jest.spyOn(options.logger, "error");
@@ -786,12 +787,12 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
@@ -799,16 +800,17 @@ describe("#start-server", () => {
                 }),
                 on: jest.fn(),
                 close: jest.fn(),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp = ({
+            const pretendApp = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
-            }: $FlowFixMe);
+            } as any;
             jest.spyOn(Express, "default").mockImplementation(() => pretendApp);
             const processOnSpy = jest.spyOn(process, "on");
             const processExitSpy = jest
                 .spyOn(process, "exit")
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 .mockReturnValue();
             await startServer(options, pretendApp);
             const errorSpy = jest.spyOn(options.logger, "error");
@@ -835,12 +837,12 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
@@ -848,9 +850,9 @@ describe("#start-server", () => {
                 }),
                 on: jest.fn(),
                 close: jest.fn(),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -858,6 +860,7 @@ describe("#start-server", () => {
             const processOnSpy = jest.spyOn(process, "on");
             const processExitSpy = jest
                 .spyOn(process, "exit")
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 .mockReturnValue();
             await startServer(options, pretendApp);
             const errorSpy = jest.spyOn(options.logger, "error");
@@ -879,12 +882,12 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
@@ -894,9 +897,9 @@ describe("#start-server", () => {
                 close: jest.fn().mockImplementation(() => {
                     throw new Error("CLOSE ERROR");
                 }),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
@@ -904,6 +907,7 @@ describe("#start-server", () => {
             const processOnSpy = jest.spyOn(process, "on");
             const processExitSpy = jest
                 .spyOn(process, "exit")
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 .mockReturnValue();
             await startServer(options, pretendApp);
             const errorSpy = jest.spyOn(options.logger, "error");
@@ -928,12 +932,12 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: () => ({
                     address: "ADDRESS",
@@ -944,16 +948,17 @@ describe("#start-server", () => {
                     // eslint-disable-next-line no-throw-literal
                     throw null;
                 }),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp = ({
+            const pretendApp = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
-            }: $FlowFixMe);
+            } as any;
             jest.spyOn(Express, "default").mockImplementation(() => pretendApp);
             const processOnSpy = jest.spyOn(process, "on");
             const processExitSpy = jest
                 .spyOn(process, "exit")
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 .mockReturnValue();
             await startServer(options, pretendApp);
             const errorSpy = jest.spyOn(options.logger, "error");
@@ -978,12 +983,12 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
                     error: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
+            } as const;
             const fakeServer = {
                 address: jest.fn(),
                 on: jest.fn(),
@@ -991,16 +996,17 @@ describe("#start-server", () => {
                     // eslint-disable-next-line no-throw-literal
                     throw {};
                 }),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp = ({
+            const pretendApp = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
-            }: $FlowFixMe);
+            } as any;
             jest.spyOn(Express, "default").mockImplementation(() => pretendApp);
             const processOnSpy = jest.spyOn(process, "on");
             const processExitSpy = jest
                 .spyOn(process, "exit")
+                // @ts-expect-error [FEI-5011] - TS2554 - Expected 1 arguments, but got 0.
                 .mockReturnValue();
             await startServer(options, pretendApp);
             const errorSpy = jest.spyOn(options.logger, "error");
@@ -1025,41 +1031,41 @@ describe("#start-server", () => {
                 name: "TEST_GATEWAY",
                 port: 42,
                 host: "127.0.0.1",
-                logger: ({
+                logger: {
                     info: jest.fn(),
-                }: $FlowFixMe),
+                } as any,
                 mode: Runtime.Test,
-            };
-            let connectionHandler;
+            } as const;
+            let connectionHandler: any;
             const fakeServer = {
                 address: jest.fn(),
-                on: jest.fn().mockImplementation((event, fn) => {
+                on: jest.fn().mockImplementation((event: any, fn: any) => {
                     if (event === "connection") {
                         connectionHandler = fn;
                     }
                 }),
                 close: jest.fn(),
-            };
+            } as const;
             const fakeConnection1 = {
                 remoteAddress: "CONNECTION_ADDRESS1",
                 remotePort: "CONNECTION_PORT1",
                 on: jest.fn(),
                 destroy: jest.fn(),
-            };
+            } as const;
             const fakeConnection2 = {
                 remoteAddress: "CONNECTION_ADDRESS2",
                 remotePort: "CONNECTION_PORT2",
                 on: jest.fn(),
                 destroy: jest.fn(),
-            };
+            } as const;
             const fakeConnection3 = {
                 remoteAddress: "CONNECTION_ADDRESS3",
                 remotePort: "CONNECTION_PORT3",
                 on: jest.fn(),
                 destroy: jest.fn(),
-            };
+            } as const;
             const listenMock = jest.fn().mockReturnValue(fakeServer);
-            const pretendApp: $FlowFixMe = {
+            const pretendApp: any = {
                 listen: listenMock,
                 use: jest.fn().mockReturnThis(),
             };
diff --git a/packages/wonder-stuff-server/src/create-logger.js b/packages/wonder-stuff-server/src/create-logger.ts
similarity index 69%
rename from packages/wonder-stuff-server/src/create-logger.js
rename to packages/wonder-stuff-server/src/create-logger.ts
index 8019aa0b..40504d79 100644
--- a/packages/wonder-stuff-server/src/create-logger.js
+++ b/packages/wonder-stuff-server/src/create-logger.ts
@@ -1,5 +1,5 @@
-// @flow
 import winston from "winston";
+// @ts-expect-error [FEI-5011] - TS2305 - Module '"winston"' has no exported member 'NpmLogLevels'.
 import type {NpmLogLevels} from "winston";
 
 import {Errors} from "./errors";
@@ -16,6 +16,7 @@ export const createLogger = ({
     defaultMetadata,
     transport,
 }: LoggingOptions): Logger => {
+    // @ts-expect-error [FEI-5011] - TS2558 - Expected 0 type arguments, but got 1.
     const winstonLogger = winston.createLogger<NpmLogLevels>({
         level,
         transports: transport ?? getLoggingTransport(mode, level),
@@ -31,7 +32,8 @@ export const createLogger = ({
     });
 
     winstonLogger.debug(
-        `Created logger (Level=${level} Mode=${(mode: string)})`,
+        // @ts-expect-error [FEI-5011] - TS2731 - Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+        `Created logger (Level=${level} Mode=${mode as string})`,
     );
 
     return winstonLogger;
diff --git a/packages/wonder-stuff-server/src/errors.js b/packages/wonder-stuff-server/src/errors.ts
similarity index 99%
rename from packages/wonder-stuff-server/src/errors.js
rename to packages/wonder-stuff-server/src/errors.ts
index a0b09b41..980561e7 100644
--- a/packages/wonder-stuff-server/src/errors.js
+++ b/packages/wonder-stuff-server/src/errors.ts
@@ -1,4 +1,3 @@
-// @flow
 import {Errors as CoreErrors} from "@khanacademy/wonder-stuff-core";
 
 /**
diff --git a/packages/wonder-stuff-server/src/get-agent-for-url.js b/packages/wonder-stuff-server/src/get-agent-for-url.ts
similarity index 97%
rename from packages/wonder-stuff-server/src/get-agent-for-url.js
rename to packages/wonder-stuff-server/src/get-agent-for-url.ts
index 7c026416..892c4ee7 100644
--- a/packages/wonder-stuff-server/src/get-agent-for-url.js
+++ b/packages/wonder-stuff-server/src/get-agent-for-url.ts
@@ -1,4 +1,3 @@
-// @flow
 import type {URL} from "url";
 import type {Agent as HttpAgent} from "http";
 import type {Agent as HttpsAgent} from "https";
@@ -37,7 +36,7 @@ import {Errors} from "./errors";
  * retaining large chunks of memory and creating memory leaks.
  */
 export const getAgentForURL = (url: URL): HttpAgent | HttpsAgent => {
-    const agentOptions = {keepAlive: true};
+    const agentOptions = {keepAlive: true} as const;
     switch (url.protocol) {
         case "http:":
             const http = require("http");
diff --git a/packages/wonder-stuff-server/src/get-logger.js b/packages/wonder-stuff-server/src/get-logger.ts
similarity index 88%
rename from packages/wonder-stuff-server/src/get-logger.js
rename to packages/wonder-stuff-server/src/get-logger.ts
index 7494cf13..81da846f 100644
--- a/packages/wonder-stuff-server/src/get-logger.js
+++ b/packages/wonder-stuff-server/src/get-logger.ts
@@ -1,5 +1,4 @@
-// @flow
-import type {$Request} from "express";
+import type {Request} from "express";
 import {getRequestLogger} from "./get-request-logger";
 import {getRootLogger} from "./root-logger";
 import type {Logger, RequestWithLog} from "./types";
@@ -17,7 +16,7 @@ import type {Logger, RequestWithLog} from "./types";
  * is no request to use for context, it is equivalent to explicitly requesting
  * the top-level logger.
  */
-export const getLogger = <TReq: RequestWithLog<$Request>>(
+export const getLogger = <TReq extends RequestWithLog<Request>>(
     request?: TReq,
 ): Logger => {
     const rootLogger = getRootLogger();
diff --git a/packages/wonder-stuff-server/src/get-logging-transport.js b/packages/wonder-stuff-server/src/get-logging-transport.ts
similarity index 89%
rename from packages/wonder-stuff-server/src/get-logging-transport.js
rename to packages/wonder-stuff-server/src/get-logging-transport.ts
index 455d19f0..1bfe3c9b 100644
--- a/packages/wonder-stuff-server/src/get-logging-transport.js
+++ b/packages/wonder-stuff-server/src/get-logging-transport.ts
@@ -1,6 +1,6 @@
-// @flow
 import stream from "stream";
 import winston from "winston";
+// @ts-expect-error [FEI-5011] - TS2724 - '"winston"' has no exported member named 'Transport'. Did you mean 'transport'? | TS2724 - '"winston"' has no exported member named 'Format'. Did you mean 'format'?
 import type {Transport, Format} from "winston";
 
 import {Runtime} from "./types";
@@ -24,7 +24,9 @@ const devFormatter = ({level, message, ...metadata}: Info): string => {
 /**
  * Build the formatters to give us some nice dev output.
  */
-const getFormatters = (mode: $Values<typeof Runtime>): Format => {
+const getFormatters = (
+    mode: (typeof Runtime)[keyof typeof Runtime],
+): Format => {
     const formatters: Array<Format> = [
         winston.format.splat(), // Allows for %s style substitutions
     ];
@@ -36,7 +38,6 @@ const getFormatters = (mode: $Values<typeof Runtime>): Format => {
      * This must be added after the cli formatter if it is to be used in
      * the dev output.
      */
-    // $FlowIgnore[prop-missing]
     formatters.push(winston.format.printf((info) => devFormatter(info)));
     return winston.format.combine(...formatters);
 };
@@ -45,7 +46,7 @@ const getFormatters = (mode: $Values<typeof Runtime>): Format => {
  * Gets the logging transport for the given mode.
  */
 export const getLoggingTransport = (
-    mode: $Values<typeof Runtime>,
+    mode: (typeof Runtime)[keyof typeof Runtime],
     logLevel: LogLevel,
 ): Transport => {
     switch (mode) {
diff --git a/packages/wonder-stuff-server/src/get-request-logger.js b/packages/wonder-stuff-server/src/get-request-logger.ts
similarity index 82%
rename from packages/wonder-stuff-server/src/get-request-logger.js
rename to packages/wonder-stuff-server/src/get-request-logger.ts
index 0e44fb9e..f9dcab8b 100644
--- a/packages/wonder-stuff-server/src/get-request-logger.js
+++ b/packages/wonder-stuff-server/src/get-request-logger.ts
@@ -1,5 +1,4 @@
-// @flow
-import type {$Request} from "express";
+import type {Request} from "express";
 import {KindError} from "@khanacademy/wonder-stuff-core";
 import {Errors} from "./errors";
 import type {Logger, RequestWithLog} from "./types";
@@ -10,8 +9,8 @@ import type {Logger, RequestWithLog} from "./types";
  * If there is a request log, it is returned, otherwise the default logger is
  * returned. If both do not exist, an error is thrown.
  */
-export const getRequestLogger = <TReq: RequestWithLog<$Request>>(
-    defaultLogger: ?Logger,
+export const getRequestLogger = <TReq extends RequestWithLog<Request>>(
+    defaultLogger?: Logger | null,
     request?: TReq,
 ): Logger => {
     if (defaultLogger == null) {
diff --git a/packages/wonder-stuff-server/src/get-runtime-mode.js b/packages/wonder-stuff-server/src/get-runtime-mode.ts
similarity index 89%
rename from packages/wonder-stuff-server/src/get-runtime-mode.js
rename to packages/wonder-stuff-server/src/get-runtime-mode.ts
index 768c346e..53c96f0c 100644
--- a/packages/wonder-stuff-server/src/get-runtime-mode.js
+++ b/packages/wonder-stuff-server/src/get-runtime-mode.ts
@@ -1,4 +1,3 @@
-// @flow
 // TODO(somewhatabstract, FEI-4174): Update eslint-plugin-import when they
 // have fixed:
 // https://github.com/import-js/eslint-plugin-import/issues/2073
@@ -14,8 +13,8 @@ import {Runtime} from "./types";
  * @returns {Runtime} The runtime mode of production, development, or test.
  */
 export const getRuntimeMode = (
-    defaultMode: $Values<typeof Runtime>,
-): $Values<typeof Runtime> => {
+    defaultMode: (typeof Runtime)[keyof typeof Runtime],
+): (typeof Runtime)[keyof typeof Runtime] => {
     switch (process.env.NODE_ENV) {
         case "test":
             return Runtime.Test;
diff --git a/packages/wonder-stuff-server/src/index.js b/packages/wonder-stuff-server/src/index.ts
similarity index 98%
rename from packages/wonder-stuff-server/src/index.js
rename to packages/wonder-stuff-server/src/index.ts
index 54eda365..41d4e542 100644
--- a/packages/wonder-stuff-server/src/index.js
+++ b/packages/wonder-stuff-server/src/index.ts
@@ -1,4 +1,3 @@
-// @flow
 export type {LogLevel, Logger, ServerOptions, RequestWithLog} from "./types";
 // TODO(somewhatabstract, FEI-4174): Update eslint-plugin-import when they
 // have fixed:
diff --git a/packages/wonder-stuff-server/src/middleware/__tests__/default-error-logging.test.js b/packages/wonder-stuff-server/src/middleware/__tests__/default-error-logging.test.ts
similarity index 81%
rename from packages/wonder-stuff-server/src/middleware/__tests__/default-error-logging.test.js
rename to packages/wonder-stuff-server/src/middleware/__tests__/default-error-logging.test.ts
index c7765f94..7870788b 100644
--- a/packages/wonder-stuff-server/src/middleware/__tests__/default-error-logging.test.js
+++ b/packages/wonder-stuff-server/src/middleware/__tests__/default-error-logging.test.ts
@@ -1,4 +1,3 @@
-//@flow
 import * as ExpressWinston from "express-winston";
 import {defaultErrorLogging} from "../default-error-logging";
 
@@ -7,8 +6,8 @@ jest.mock("express-winston");
 describe("#defaultErrorLogging", () => {
     it("should return express-winston error logger", () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendErrorMiddleware = ({}: $FlowFixMe);
+        const pretendLogger = {} as any;
+        const pretendErrorMiddleware = {} as any;
         jest.spyOn(ExpressWinston, "errorLogger").mockReturnValue(
             pretendErrorMiddleware,
         );
@@ -22,8 +21,8 @@ describe("#defaultErrorLogging", () => {
 
     it("should pass given logger to express winston", () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendErrorMiddleware = ({}: $FlowFixMe);
+        const pretendLogger = {} as any;
+        const pretendErrorMiddleware = {} as any;
         const errorLoggerSpy = jest
             .spyOn(ExpressWinston, "errorLogger")
             .mockReturnValue(pretendErrorMiddleware);
diff --git a/packages/wonder-stuff-server/src/middleware/__tests__/default-request-logging.test.js b/packages/wonder-stuff-server/src/middleware/__tests__/default-request-logging.test.ts
similarity index 81%
rename from packages/wonder-stuff-server/src/middleware/__tests__/default-request-logging.test.js
rename to packages/wonder-stuff-server/src/middleware/__tests__/default-request-logging.test.ts
index 2851d840..c490dcc6 100644
--- a/packages/wonder-stuff-server/src/middleware/__tests__/default-request-logging.test.js
+++ b/packages/wonder-stuff-server/src/middleware/__tests__/default-request-logging.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import * as ExpressWinston from "express-winston";
 import {defaultRequestLogging} from "../default-request-logging";
 
@@ -7,8 +6,8 @@ jest.mock("express-winston");
 describe("#defaultRequestLogging", () => {
     it("should return express-winston middleware", async () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendExpressWinstonMiddleware = ({}: $FlowFixMe);
+        const pretendLogger = {} as any;
+        const pretendExpressWinstonMiddleware = {} as any;
         jest.spyOn(ExpressWinston, "logger").mockReturnValue(
             pretendExpressWinstonMiddleware,
         );
@@ -22,8 +21,8 @@ describe("#defaultRequestLogging", () => {
 
     it("should create middleware with logger", async () => {
         // Arrange
-        const pretendLogger = ({}: $FlowFixMe);
-        const pretendExpressWinstonMiddleware = ({}: $FlowFixMe);
+        const pretendLogger = {} as any;
+        const pretendExpressWinstonMiddleware = {} as any;
         const middlewareSpy = jest
             .spyOn(ExpressWinston, "logger")
             .mockReturnValue(pretendExpressWinstonMiddleware);
diff --git a/packages/wonder-stuff-server/src/middleware/default-error-logging.js b/packages/wonder-stuff-server/src/middleware/default-error-logging.js
deleted file mode 100644
index 3ac97f32..00000000
--- a/packages/wonder-stuff-server/src/middleware/default-error-logging.js
+++ /dev/null
@@ -1,19 +0,0 @@
-// @flow
-import expressWinston from "express-winston";
-
-import type {Middleware, $Request, $Response} from "express";
-import type {Logger} from "../types";
-
-/**
- * Create middleware for reporting errors.
- */
-export const defaultErrorLogging = <TReq: $Request, TRes: $Response>(
-    logger: Logger,
-): Middleware<TReq, TRes> =>
-    /**
-     * Express-winston types aren't parameterized, so we suppress the error.
-     */
-    expressWinston.errorLogger({
-        level: "error",
-        winstonInstance: logger,
-    });
diff --git a/packages/wonder-stuff-server/src/middleware/default-error-logging.ts b/packages/wonder-stuff-server/src/middleware/default-error-logging.ts
new file mode 100644
index 00000000..2485590f
--- /dev/null
+++ b/packages/wonder-stuff-server/src/middleware/default-error-logging.ts
@@ -0,0 +1,22 @@
+import expressWinston from "express-winston";
+
+// @ts-expect-error [FEI-5011] - TS2305 - Module '"express"' has no exported member 'Middleware'.
+import type {Middleware, Request, Response} from "express";
+import type {Logger} from "../types";
+
+/**
+ * Create middleware for reporting errors.
+ */
+export const defaultErrorLogging = <
+    TReq extends Request,
+    TRes extends Response,
+>(
+    logger: Logger,
+): Middleware<TReq, TRes>
+/**
+ * Express-winston types aren't parameterized, so we suppress the error.
+ */ =>
+    expressWinston.errorLogger({
+        level: "error",
+        winstonInstance: logger,
+    });
diff --git a/packages/wonder-stuff-server/src/middleware/default-request-logging.js b/packages/wonder-stuff-server/src/middleware/default-request-logging.ts
similarity index 64%
rename from packages/wonder-stuff-server/src/middleware/default-request-logging.js
rename to packages/wonder-stuff-server/src/middleware/default-request-logging.ts
index e6ccadd6..2043a1c8 100644
--- a/packages/wonder-stuff-server/src/middleware/default-request-logging.js
+++ b/packages/wonder-stuff-server/src/middleware/default-request-logging.ts
@@ -1,18 +1,21 @@
-// @flow
 import expressWinston from "express-winston";
 
-import type {Middleware, $Request, $Response} from "express";
+// @ts-expect-error [FEI-5011] - TS2305 - Module '"express"' has no exported member 'Middleware'.
+import type {Middleware, Request, Response} from "express";
 import type {Logger} from "../types";
 
 /**
  * Create middleware for tracking requests.
  */
-export const defaultRequestLogging = <TReq: $Request, TRes: $Response>(
+export const defaultRequestLogging = <
+    TReq extends Request,
+    TRes extends Response,
+>(
     logger: Logger,
-): Middleware<TReq, TRes> =>
-    /**
-     * We use express-winston to log requests for us.
-     */
+): Middleware<TReq, TRes>
+/**
+ * We use express-winston to log requests for us.
+ */ =>
     expressWinston.logger({
         /**
          * Specify the level that this logger logs at.
diff --git a/packages/wonder-stuff-server/src/middleware/index.js b/packages/wonder-stuff-server/src/middleware/index.ts
similarity index 93%
rename from packages/wonder-stuff-server/src/middleware/index.js
rename to packages/wonder-stuff-server/src/middleware/index.ts
index d6fa3cfc..099581b4 100644
--- a/packages/wonder-stuff-server/src/middleware/index.js
+++ b/packages/wonder-stuff-server/src/middleware/index.ts
@@ -1,3 +1,2 @@
-// @flow
 export {defaultErrorLogging} from "./default-error-logging";
 export {defaultRequestLogging} from "./default-request-logging";
diff --git a/packages/wonder-stuff-server/src/root-logger.js b/packages/wonder-stuff-server/src/root-logger.ts
similarity index 78%
rename from packages/wonder-stuff-server/src/root-logger.js
rename to packages/wonder-stuff-server/src/root-logger.ts
index 85949ca2..2915565c 100644
--- a/packages/wonder-stuff-server/src/root-logger.js
+++ b/packages/wonder-stuff-server/src/root-logger.ts
@@ -1,14 +1,13 @@
-// @flow
 import {KindError} from "@khanacademy/wonder-stuff-core";
 import {Errors} from "./errors";
 import type {Logger} from "./types";
 
-let rootLogger: ?Logger = null;
+let rootLogger: Logger | null | undefined = null;
 
 /**
  * Get the root-level logger.
  */
-export const getRootLogger: () => ?Logger = () => rootLogger;
+export const getRootLogger: () => Logger | null | undefined = () => rootLogger;
 
 /**
  * Set the root-level logger.
diff --git a/packages/wonder-stuff-server/src/start-server.js b/packages/wonder-stuff-server/src/start-server.ts
similarity index 90%
rename from packages/wonder-stuff-server/src/start-server.js
rename to packages/wonder-stuff-server/src/start-server.ts
index 87c64561..490e8b86 100644
--- a/packages/wonder-stuff-server/src/start-server.js
+++ b/packages/wonder-stuff-server/src/start-server.ts
@@ -1,5 +1,4 @@
-// @flow
-import type {$Application, $Request, $Response} from "express";
+import type {Application, Request, Response} from "express";
 import express from "express";
 import {setRootLogger} from "./root-logger";
 // TODO(somewhatabstract, FEI-4174): Update eslint-plugin-import when they
@@ -19,8 +18,8 @@ import * as middleware from "./middleware/index";
  * options.
  */
 export async function startServer<
-    TReq: RequestWithLog<$Request>,
-    TRes: $Response,
+    TReq extends RequestWithLog<Request>,
+    TRes extends Response,
 >(
     {
         logger,
@@ -33,8 +32,9 @@ export async function startServer<
         includeErrorMiddleware = true,
         includeRequestMiddleware = true,
     }: ServerOptions,
-    app: $Application<TReq, TRes>,
-): Promise<?http$Server> {
+    // @ts-expect-error [FEI-5011] - TS2315 - Type 'Application' is not generic.
+    app: Application<TReq, TRes>,
+): Promise<http.Server | null | undefined> {
     /**
      * Setup logging.
      * We create the root logger once and then share it via a singleton.
@@ -57,14 +57,12 @@ export async function startServer<
     ) {
         try {
             /* eslint-disable import/no-unassigned-import */
-            // $FlowIgnore[cannot-resolve-module]
-            // $FlowIgnore[untyped-import]
             require("heapdump");
             /* eslint-enable import/no-unassigned-import */
             logger.debug(
                 `Heapdumps enabled. To create a heap snapshot at any time, run "kill -USR2 ${process.pid}".`,
             );
-        } catch (e) {
+        } catch (e: any) {
             // heapdump is an optional peer dependency, so if it is absent,
             // that is perfectly fine.
         }
@@ -73,6 +71,7 @@ export async function startServer<
     /**
      * Add middleware per options.
      */
+    // @ts-expect-error [FEI-5011] - TS2558 - Expected 0 type arguments, but got 2.
     const appWithMiddleware = express<TReq, TRes>();
     if (includeRequestMiddleware) {
         appWithMiddleware.use(middleware.defaultRequestLogging(logger));
@@ -88,10 +87,10 @@ export async function startServer<
      * We need the variable so we can reference it inside the error handling
      * callback. Feels a bit nasty, but it works.
      */
-    const server: ?http$Server = appWithMiddleware.listen(
+    const server: http.Server | null | undefined = appWithMiddleware.listen(
         port,
         host,
-        (err: ?Error) => {
+        (err?: Error | null) => {
             if (server == null || err != null) {
                 logger.error(
                     `${name} appears not to have started: ${
@@ -124,17 +123,16 @@ export async function startServer<
      * trying to close. So, let's track them and provide a means for us to\
      * destroy them.
      */
-    const connections: {|
-        [string]: net$Socket,
-    |} = {};
+    const connections: {
+        [key: string]: net.Socket;
+    } = {};
     const closeConnections = () => {
         for (const connection of Object.values(connections)) {
             // Connection is type mixed, so we need to tell flow this is OK.
-            // $FlowIgnore[incompatible-use]
             connection.destroy();
         }
     };
-    server?.on("connection", (connection: net$Socket) => {
+    server?.on("connection", (connection: net.Socket) => {
         const key = `${connection.remoteAddress ?? ""}:${
             connection.remotePort
         }`;
@@ -166,6 +164,7 @@ export async function startServer<
         logger.info("SIGINT received, shutting down server.");
 
         try {
+            // @ts-expect-error [FEI-5011] - TS7006 - Parameter 'err' implicitly has an 'any' type.
             server.close((err) => {
                 if (err) {
                     logger.error(
@@ -182,7 +181,7 @@ export async function startServer<
                 }
             });
             closeConnections();
-        } catch (err) {
+        } catch (err: any) {
             logger.error(
                 `Error closing server: ${err?.message || "Unknown Error"}`,
                 {
diff --git a/packages/wonder-stuff-server/src/types.js b/packages/wonder-stuff-server/src/types.ts
similarity index 68%
rename from packages/wonder-stuff-server/src/types.js
rename to packages/wonder-stuff-server/src/types.ts
index ad117f19..16527e9c 100644
--- a/packages/wonder-stuff-server/src/types.js
+++ b/packages/wonder-stuff-server/src/types.ts
@@ -1,4 +1,4 @@
-// @flow
+// @ts-expect-error [FEI-5011] - TS2305 - Module '"winston"' has no exported member 'NpmLogLevels'. | TS2724 - '"winston"' has no exported member named 'Info'. Did you mean 'info'? | TS2724 - '"winston"' has no exported member named 'Transport'. Did you mean 'transport'?
 import type {
     NpmLogLevels,
     Logger as WinstonLogger,
@@ -6,7 +6,7 @@ import type {
     Transport,
 } from "winston";
 
-import type {$Request} from "express";
+import type {Request} from "express";
 
 /**
  * Describes logging metdata.
@@ -16,11 +16,12 @@ export type Info = WinstonInfo<NpmLogLevels>;
 /**
  * Defines the different log levels.
  */
-export type LogLevel = $Keys<NpmLogLevels>;
+export type LogLevel = keyof NpmLogLevels;
 
 /**
  * Describes the interface for logging gateway activity.
  */
+// @ts-expect-error [FEI-5011] - TS2315 - Type 'Logger' is not generic.
 export type Logger = WinstonLogger<NpmLogLevels>;
 
 /**
@@ -28,10 +29,10 @@ export type Logger = WinstonLogger<NpmLogLevels>;
  */
 // TODO(FEI-5001): Replace with TS enum
 export const Runtime = {
-    Production: ("production": "production"),
-    Development: ("development": "development"),
-    Test: ("test": "test"),
-};
+    Production: "production" as const,
+    Development: "development" as const,
+    Test: "test" as const,
+} as const;
 
 /**
  * Options to configure logging.
@@ -40,25 +41,22 @@ export type LoggingOptions = {
     /**
      * The runtime mode.
      */
-    mode: $Values<typeof Runtime>,
-
+    mode: (typeof Runtime)[keyof typeof Runtime];
     /**
      * Log only if the level of a logged entry is less than or equal to this
      * level. Enables filtering out of debug message in production, for example.
      */
-    level: LogLevel,
-
+    level: LogLevel;
     /**
      * Metadata to attach to every logged entry, by default.
      * Defaults to null.
      */
-    defaultMetadata?: {...} | (() => {...}),
-
+    defaultMetadata?: Record<any, any> | (() => Record<any, any>);
     /**
      * The transport to use for handling log entries. When not specified or
      * null, this will be determined using `getLoggingTransport`.
      */
-    transport?: ?Transport,
+    transport?: Transport | null | undefined;
 };
 
 /**
@@ -68,28 +66,23 @@ export type ServerOptions = {
     /**
      * The name of the server.
      */
-    +name: string,
-
+    readonly name: string;
     /**
      * The port on which the server should listen.
      */
-    +port: number,
-
+    readonly port: number;
     /**
      * The hostname to which the server should bind.
      */
-    +host: string,
-
+    readonly host: string;
     /**
      * The logger to use for logging.
      */
-    +logger: Logger,
-
+    readonly logger: Logger;
     /**
      * What runtime mode the server is running under.
      */
-    +mode: $Values<typeof Runtime>,
-
+    readonly mode: (typeof Runtime)[keyof typeof Runtime];
     /**
      * Optional value in milliseconds for keepalive timeout of the server.
      * For running in Google Cloud, this should be higher than the load
@@ -100,8 +93,7 @@ export type ServerOptions = {
      *
      * Defaults to 90000.
      */
-    +keepAliveTimeout?: number,
-
+    readonly keepAliveTimeout?: number;
     /**
      * When `true`, the "heapdump" package will be loaded, allowing for
      * heap dumps to be generated on demand using `kill -USR2 <pid>` where
@@ -110,21 +102,19 @@ export type ServerOptions = {
      * Defaults to `false` in production mode, and `true` in all other modes.
      * Set explicitly to `false` to disable heap dumps in all modes.
      */
-    +allowHeapDumps?: boolean,
-
+    readonly allowHeapDumps?: boolean;
     /**
      * When `true` or omitted, the default express-winston-based error logging
      * middleware is included. When `false`, this is not included.
      */
-    +includeErrorMiddleware?: boolean,
-
+    readonly includeErrorMiddleware?: boolean;
     /**
      * When `true` or omitted, the default express-winston-based request logging
      * middleware is included. When `false`, this is not included.
      */
-    +includeRequestMiddleware?: boolean,
+    readonly includeRequestMiddleware?: boolean;
 };
 
-export type RequestWithLog<TReq: $Request> = TReq & {
-    log?: Logger,
+export type RequestWithLog<TReq extends Request> = TReq & {
+    log?: Logger;
 };
diff --git a/packages/wonder-stuff-testing/src/__tests__/data-factory-for.test.js b/packages/wonder-stuff-testing/src/__tests__/data-factory-for.test.ts
similarity index 65%
rename from packages/wonder-stuff-testing/src/__tests__/data-factory-for.test.js
rename to packages/wonder-stuff-testing/src/__tests__/data-factory-for.test.ts
index ae114de5..bae452ad 100644
--- a/packages/wonder-stuff-testing/src/__tests__/data-factory-for.test.js
+++ b/packages/wonder-stuff-testing/src/__tests__/data-factory-for.test.ts
@@ -1,10 +1,9 @@
-// @flow
 import {dataFactoryFor} from "../data-factory-for";
 
 describe("dataFactoryFor", () => {
     describe("returns a function that", () => {
         it("should return a clone of the default data", () => {
-            const BASE_OBJECT = {x: 5, y: 10};
+            const BASE_OBJECT = {x: 5, y: 10} as const;
 
             const dataFactory = dataFactoryFor(BASE_OBJECT);
 
@@ -14,10 +13,11 @@ describe("dataFactoryFor", () => {
         });
 
         it("should merge object passed to factory with the base object", () => {
-            const BASE_OBJECT = {x: 5, y: 10};
+            const BASE_OBJECT = {x: 5, y: 10} as const;
 
             const dataFactory = dataFactoryFor(BASE_OBJECT);
 
+            // @ts-expect-error [FEI-5011] - TS2322 - Type '100' is not assignable to type '5 | undefined'.
             const data = dataFactory({x: 100});
             expect(data).toEqual({
                 x: 100,
@@ -29,12 +29,14 @@ describe("dataFactoryFor", () => {
             const BASE_OBJECT = {
                 p: {x: 5, y: 10},
                 q: {x: 0, y: 1},
-            };
+            } as const;
 
             const dataFactory = dataFactoryFor(BASE_OBJECT);
 
-            const p = {x: 20, y: 30};
+            const p = {x: 20, y: 30} as const;
+            // @ts-expect-error [FEI-5011] - TS2322 - Type '{ readonly x: 20; readonly y: 30; }' is not assignable to type '{ readonly x: 5; readonly y: 10; }'.
             const data = dataFactory({p});
+            // @ts-expect-error [FEI-5011] - TS2540 - Cannot assign to 'x' because it is a read-only property.
             data.p.x = 100;
 
             expect(p).toEqual({x: 20, y: 30});
diff --git a/packages/wonder-stuff-testing/src/data-factory-for.js b/packages/wonder-stuff-testing/src/data-factory-for.ts
similarity index 89%
rename from packages/wonder-stuff-testing/src/data-factory-for.js
rename to packages/wonder-stuff-testing/src/data-factory-for.ts
index 13e63485..f9a68758 100644
--- a/packages/wonder-stuff-testing/src/data-factory-for.js
+++ b/packages/wonder-stuff-testing/src/data-factory-for.ts
@@ -1,4 +1,3 @@
-// @flow
 import {clone} from "@khanacademy/wonder-stuff-core";
 
 /**
@@ -46,13 +45,14 @@ import {clone} from "@khanacademy/wonder-stuff-core";
  *     }
  */
 export const dataFactoryFor =
-    <T>(baseObject: T): ((partialObject?: $Partial<T>) => T) =>
+    <T>(baseObject: T): ((partialObject?: Partial<T>) => T) =>
     <T>(
         // $FlowIgnore[incompatible-type]: Flow thinks that {} can't be assigned to Partial<T>
-        partialObject: $Partial<T> = Object.freeze({}),
+        partialObject: Partial<T> = Object.freeze({}),
     ): T => {
         // NOTE: we clone the result to prevent tests from modifying
         // either `defaultObject` or `partialObject` when performing
         // deep updates on the return object returned by the factory.
+        // @ts-expect-error [FEI-5011] - TS2322 - Type 'T & Partial<T>' is not assignable to type 'T'.
         return clone({...baseObject, ...partialObject});
     };
diff --git a/packages/wonder-stuff-testing/src/index.js b/packages/wonder-stuff-testing/src/index.ts
similarity index 90%
rename from packages/wonder-stuff-testing/src/index.js
rename to packages/wonder-stuff-testing/src/index.ts
index 9332de4b..89710067 100644
--- a/packages/wonder-stuff-testing/src/index.js
+++ b/packages/wonder-stuff-testing/src/index.ts
@@ -1,3 +1,2 @@
-// @flow
 export * as jest from "./jest/index";
 export {dataFactoryFor} from "./data-factory-for";
diff --git a/packages/wonder-stuff-testing/src/jest/__tests__/isolate-modules.test.js b/packages/wonder-stuff-testing/src/jest/__tests__/isolate-modules.test.ts
similarity index 99%
rename from packages/wonder-stuff-testing/src/jest/__tests__/isolate-modules.test.js
rename to packages/wonder-stuff-testing/src/jest/__tests__/isolate-modules.test.ts
index 0343564d..1584f60a 100644
--- a/packages/wonder-stuff-testing/src/jest/__tests__/isolate-modules.test.js
+++ b/packages/wonder-stuff-testing/src/jest/__tests__/isolate-modules.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {isolateModules} from "../isolate-modules";
 import * as AssertJest from "../internal/assert-jest";
 
diff --git a/packages/wonder-stuff-testing/src/jest/__tests__/wait.test.js b/packages/wonder-stuff-testing/src/jest/__tests__/wait.test.ts
similarity index 99%
rename from packages/wonder-stuff-testing/src/jest/__tests__/wait.test.js
rename to packages/wonder-stuff-testing/src/jest/__tests__/wait.test.ts
index 8dceb9b6..6ef755f5 100644
--- a/packages/wonder-stuff-testing/src/jest/__tests__/wait.test.js
+++ b/packages/wonder-stuff-testing/src/jest/__tests__/wait.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {wait, waitForAnimationFrame} from "../wait";
 import * as VerifyRealTimers from "../internal/verify-real-timers";
 import * as UnverifiedWait from "../internal/unverified-wait";
diff --git a/packages/wonder-stuff-testing/src/jest/index.js b/packages/wonder-stuff-testing/src/jest/index.ts
similarity index 89%
rename from packages/wonder-stuff-testing/src/jest/index.js
rename to packages/wonder-stuff-testing/src/jest/index.ts
index b7e9861b..b0f7128a 100644
--- a/packages/wonder-stuff-testing/src/jest/index.js
+++ b/packages/wonder-stuff-testing/src/jest/index.ts
@@ -1,3 +1,2 @@
-// @flow
 export {isolateModules} from "./isolate-modules";
 export {wait} from "./wait";
diff --git a/packages/wonder-stuff-testing/src/jest/internal/__tests__/assert-jest.test.js b/packages/wonder-stuff-testing/src/jest/internal/__tests__/assert-jest.test.ts
similarity index 98%
rename from packages/wonder-stuff-testing/src/jest/internal/__tests__/assert-jest.test.js
rename to packages/wonder-stuff-testing/src/jest/internal/__tests__/assert-jest.test.ts
index 6a0542c5..6997b70e 100644
--- a/packages/wonder-stuff-testing/src/jest/internal/__tests__/assert-jest.test.js
+++ b/packages/wonder-stuff-testing/src/jest/internal/__tests__/assert-jest.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {assertJest} from "../assert-jest";
 import * as IsRunningInJest from "../is-running-in-jest";
 
diff --git a/packages/wonder-stuff-testing/src/jest/internal/__tests__/unverified-wait.test.js b/packages/wonder-stuff-testing/src/jest/internal/__tests__/unverified-wait.test.ts
similarity index 72%
rename from packages/wonder-stuff-testing/src/jest/internal/__tests__/unverified-wait.test.js
rename to packages/wonder-stuff-testing/src/jest/internal/__tests__/unverified-wait.test.ts
index 8667f49c..392010e1 100644
--- a/packages/wonder-stuff-testing/src/jest/internal/__tests__/unverified-wait.test.js
+++ b/packages/wonder-stuff-testing/src/jest/internal/__tests__/unverified-wait.test.ts
@@ -1,4 +1,3 @@
-// @flow
 import {unverifiedWait} from "../unverified-wait";
 
 describe("#unverifiedWait", () => {
@@ -15,7 +14,7 @@ describe("#unverifiedWait", () => {
         // Arrange
         const setTimeoutSpy = jest
             .spyOn(global, "setTimeout")
-            .mockImplementation((fn) => fn());
+            .mockImplementation((fn: any) => fn());
 
         // Act
         await unverifiedWait(42, 1);
@@ -28,7 +27,7 @@ describe("#unverifiedWait", () => {
         // Arrange
         const setTimeoutSpy = jest
             .spyOn(global, "setTimeout")
-            .mockImplementation((fn) => fn());
+            .mockImplementation((fn: any) => fn());
 
         // Act
         await unverifiedWait(1, 42);
@@ -39,11 +38,12 @@ describe("#unverifiedWait", () => {
 
     it("should resolve one promise per count", async () => {
         // Arrange
-        jest.spyOn(global, "setTimeout").mockImplementation((fn) => fn());
+        jest.spyOn(global, "setTimeout").mockImplementation((fn: any) => fn());
 
         const countResolves = jest.fn();
-        global.Promise = jest.fn().mockImplementation((fn) => {
-            return new RealPromise((resolve, reject) => {
+        // @ts-expect-error [FEI-5011] - TS2740 - Type 'Mock<any, any, any>' is missing the following properties from type 'PromiseConstructor': all, race, reject, resolve, and 2 more.
+        global.Promise = jest.fn().mockImplementation((fn: any) => {
+            return new RealPromise((resolve: any, reject: any) => {
                 const countedResolve = () => {
                     countResolves();
                     resolve();
diff --git a/packages/wonder-stuff-testing/src/jest/internal/__tests__/verify-real-timers.test.js b/packages/wonder-stuff-testing/src/jest/internal/__tests__/verify-real-timers.test.ts
similarity index 99%
rename from packages/wonder-stuff-testing/src/jest/internal/__tests__/verify-real-timers.test.js
rename to packages/wonder-stuff-testing/src/jest/internal/__tests__/verify-real-timers.test.ts
index 5c105f35..d4e54704 100644
--- a/packages/wonder-stuff-testing/src/jest/internal/__tests__/verify-real-timers.test.js
+++ b/packages/wonder-stuff-testing/src/jest/internal/__tests__/verify-real-timers.test.ts
@@ -1,5 +1,4 @@
 /* eslint-disable no-console */
-// @flow
 import {Errors} from "@khanacademy/wonder-stuff-core";
 import * as AssertJest from "../assert-jest";
 import {verifyRealTimers} from "../verify-real-timers";
diff --git a/packages/wonder-stuff-testing/src/jest/internal/assert-jest.js b/packages/wonder-stuff-testing/src/jest/internal/assert-jest.ts
similarity index 97%
rename from packages/wonder-stuff-testing/src/jest/internal/assert-jest.js
rename to packages/wonder-stuff-testing/src/jest/internal/assert-jest.ts
index c3d60958..8f5898ff 100644
--- a/packages/wonder-stuff-testing/src/jest/internal/assert-jest.js
+++ b/packages/wonder-stuff-testing/src/jest/internal/assert-jest.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError, Errors} from "@khanacademy/wonder-stuff-core";
 import {isRunningInJest} from "./is-running-in-jest";
 
diff --git a/packages/wonder-stuff-testing/src/jest/internal/is-running-in-jest.js b/packages/wonder-stuff-testing/src/jest/internal/is-running-in-jest.ts
similarity index 97%
rename from packages/wonder-stuff-testing/src/jest/internal/is-running-in-jest.js
rename to packages/wonder-stuff-testing/src/jest/internal/is-running-in-jest.ts
index bec8b008..fcf4bbe4 100644
--- a/packages/wonder-stuff-testing/src/jest/internal/is-running-in-jest.js
+++ b/packages/wonder-stuff-testing/src/jest/internal/is-running-in-jest.ts
@@ -1,4 +1,3 @@
-// @flow
 // istanbul ignore file
 /**
  * Determine if jest is running or not.
diff --git a/packages/wonder-stuff-testing/src/jest/internal/unverified-wait.js b/packages/wonder-stuff-testing/src/jest/internal/unverified-wait.js
deleted file mode 100644
index 7853782f..00000000
--- a/packages/wonder-stuff-testing/src/jest/internal/unverified-wait.js
+++ /dev/null
@@ -1,12 +0,0 @@
-// @flow
-export const unverifiedWait = (delay: number, count: number): Promise<void> =>
-    new Promise((resolve, reject) => {
-        // eslint-disable-next-line no-restricted-syntax
-        setTimeout(() => {
-            if (count > 1) {
-                resolve(unverifiedWait(delay, count - 1));
-            } else {
-                resolve();
-            }
-        }, delay);
-    });
diff --git a/packages/wonder-stuff-testing/src/jest/internal/unverified-wait.ts b/packages/wonder-stuff-testing/src/jest/internal/unverified-wait.ts
new file mode 100644
index 00000000..a27c6b06
--- /dev/null
+++ b/packages/wonder-stuff-testing/src/jest/internal/unverified-wait.ts
@@ -0,0 +1,18 @@
+export const unverifiedWait = (delay: number, count: number): Promise<void> =>
+    new Promise(
+        (
+            resolve: (result: Promise<undefined> | undefined) => void,
+            reject: (error?: any) => void,
+        ) => {
+            // eslint-disable-next-line no-restricted-syntax
+            setTimeout(() => {
+                if (count > 1) {
+                    // @ts-expect-error [FEI-5011] - TS2345 - Argument of type 'Promise<void>' is not assignable to parameter of type 'Promise<undefined>'.
+                    resolve(unverifiedWait(delay, count - 1));
+                } else {
+                    // @ts-expect-error [FEI-5011] - TS2794 - Expected 1 arguments, but got 0. Did you forget to include 'void' in your type argument to 'Promise'?
+                    resolve();
+                }
+            }, delay);
+        },
+    );
diff --git a/packages/wonder-stuff-testing/src/jest/internal/verify-real-timers.js b/packages/wonder-stuff-testing/src/jest/internal/verify-real-timers.ts
similarity index 94%
rename from packages/wonder-stuff-testing/src/jest/internal/verify-real-timers.js
rename to packages/wonder-stuff-testing/src/jest/internal/verify-real-timers.ts
index 3fdcf4f5..10dd316d 100644
--- a/packages/wonder-stuff-testing/src/jest/internal/verify-real-timers.js
+++ b/packages/wonder-stuff-testing/src/jest/internal/verify-real-timers.ts
@@ -1,4 +1,3 @@
-// @flow
 import {KindError, Errors} from "@khanacademy/wonder-stuff-core";
 import {assertJest} from "./assert-jest";
 
@@ -14,7 +13,6 @@ export const verifyRealTimers = () => {
     // change this behavior we would silently start just working.
     // eslint-disable-next-line no-console
     const oldWarn = console.warn;
-    // $FlowIgnore[cannot-write]
     console.warn = () => {}; // eslint-disable-line no-console
 
     try {
@@ -31,7 +29,6 @@ export const verifyRealTimers = () => {
             );
         }
     } finally {
-        // $FlowIgnore[cannot-write]
         console.warn = oldWarn; // eslint-disable-line no-console
     }
 };
diff --git a/packages/wonder-stuff-testing/src/jest/isolate-modules.js b/packages/wonder-stuff-testing/src/jest/isolate-modules.ts
similarity index 90%
rename from packages/wonder-stuff-testing/src/jest/isolate-modules.js
rename to packages/wonder-stuff-testing/src/jest/isolate-modules.ts
index 08c899b6..bfb2a044 100644
--- a/packages/wonder-stuff-testing/src/jest/isolate-modules.js
+++ b/packages/wonder-stuff-testing/src/jest/isolate-modules.ts
@@ -1,4 +1,3 @@
-// @flow
 import {assertJest} from "./internal/assert-jest";
 
 /**
@@ -23,6 +22,6 @@ export const isolateModules = <T>(action: () => T): T => {
     // We know that we'll have a result of the appropriate type at this point.
     // We could use a promise to make everything happy, but this doesn't need
     // to be async, so why bother.
-    // $FlowIgnore[incompatible-return]
+    // @ts-expect-error [FEI-5011] - TS2454 - Variable 'result' is used before being assigned.
     return result;
 };
diff --git a/packages/wonder-stuff-testing/src/jest/wait.js b/packages/wonder-stuff-testing/src/jest/wait.ts
similarity index 93%
rename from packages/wonder-stuff-testing/src/jest/wait.js
rename to packages/wonder-stuff-testing/src/jest/wait.ts
index 1fc6e857..3ce85f4a 100644
--- a/packages/wonder-stuff-testing/src/jest/wait.js
+++ b/packages/wonder-stuff-testing/src/jest/wait.ts
@@ -1,23 +1,21 @@
-// @flow
 import {verifyRealTimers} from "./internal/verify-real-timers";
 import {unverifiedWait} from "./internal/unverified-wait";
 import {assertJest} from "./internal/assert-jest";
 
 assertJest();
 
-type WaitOptions = {|
+type WaitOptions = {
     /**
      * The time in milliseconds to wait on each wait.
      * Defaults to 0. Any number less than 0 will be treated as 0.
      */
-    delay?: number,
-
+    delay?: number;
     /**
      * The number of times to wait.
      * Defaults to 1. Any number below 1 will be treated as 1.
      */
-    count?: number,
-|};
+    count?: number;
+};
 
 /**
  * Wait for the given delay as many times as indicated.