diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 5befb8fb..2ebc3de4 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -26,4 +26,5 @@ jobs:
         run: |
           npm install
           npm run build --if-present
+          npm run format:check
           npm test
diff --git a/.prettierignore b/.prettierignore
index 047e5087..a08d593d 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1,3 +1,9 @@
 *.d.ts
 test/data/
 /example
+
+# output files
+/main.js
+/lib/**/*.js
+/parsers/**/*.js
+/test/**/*.js
diff --git a/package.json b/package.json
index 52c6a3ea..74fecb34 100644
--- a/package.json
+++ b/package.json
@@ -28,6 +28,7 @@
     "build": "npm run clean && tsc",
     "lint": "eslint --ext .ts .",
     "format": "prettier --write .",
+    "format:check": "prettier --check .",
     "clean": "tsc --build --clean",
     "prepare": "npm run build",
     "postpack": "npm run clean"