diff --git a/.changeset/late-sheep-rush.md b/.changeset/late-sheep-rush.md
new file mode 100644
index 0000000000..07c7162a8b
--- /dev/null
+++ b/.changeset/late-sheep-rush.md
@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus": patch
+---
+
+Internal: make the exhaustive test tool for PerseusItem parsing find the shortest input file that repros each failure
diff --git a/packages/perseus/src/util/parse-perseus-json/exhaustive-test-tool/index.ts b/packages/perseus/src/util/parse-perseus-json/exhaustive-test-tool/index.ts
index e3d5880d09..f50ea2bede 100755
--- a/packages/perseus/src/util/parse-perseus-json/exhaustive-test-tool/index.ts
+++ b/packages/perseus/src/util/parse-perseus-json/exhaustive-test-tool/index.ts
@@ -75,7 +75,11 @@ async function testFile(path: string, outputDir: string) {
                 desc,
                 "utf-8",
             );
-            await fs.writeFile(
+            // We'd like to find the shortest assessment item that reproduces
+            // each mismatch, to keep our regression tests succinct and
+            // readable. To that end, we only update the item.json file if the
+            // current item is shorter than the one already on disk.
+            await writeFileIfShorterThanExisting(
                 join(outputDir, hash, "item.json"),
                 String(JSON.stringify(rawItem)),
                 "utf-8",
@@ -124,6 +128,21 @@ function typeName(value: unknown): string {
     return typeof value;
 }
 
+async function writeFileIfShorterThanExisting(
+    path: string,
+    content: string,
+    encoding: "utf-8", // TODO(benchristel): add more encodings if needed
+) {
+    const size = await fs
+        .stat(path)
+        .then((stat) => stat.size)
+        .catch(() => null);
+    const contentLength = Buffer.byteLength(content, encoding);
+    if (size == null || contentLength < size) {
+        await fs.writeFile(path, content, encoding);
+    }
+}
+
 async function* listFilesRecursively(dir: string) {
     for await (const entry of await fs.opendir(dir, {recursive: true})) {
         if (entry.isFile()) {