diff --git a/.github/workflows/docs-validate-nav-build.yml b/.github/workflows/docs-validate-nav-build.yml
index 674ca22a6ae..87a4e070c5e 100644
--- a/.github/workflows/docs-validate-nav-build.yml
+++ b/.github/workflows/docs-validate-nav-build.yml
@@ -40,6 +40,15 @@ jobs:
         run: |
           diff -q docs/nav.js docs/nav.js.original || (echo "Generated nav.js differs from committed version. Run 'npm run build' and commit the updated file." && exit 1)
 
+      # We do this after checking that nav.js matches nav.ts, to avoid confusing error messages if an author updates one but not the other.
+      # If the .ts and .js are in sync, it doesn't matter which one we check against here.
+      - name: Check that all files are listed in nav.js
+        working-directory: docs
+        run: |
+          cp docs/nav.js docs/nav.mjs
+          find docs -name '*.md' | sed 's!^docs/!!' > scripts/docs-files.txt
+          node scripts/checkNav.mjs docs-files.txt
+
       - name: Restore original nav.js
         working-directory: docs
         if: success() || failure()
diff --git a/docs/scripts/checkNav.mjs b/docs/scripts/checkNav.mjs
new file mode 100644
index 00000000000..62f745ba690
--- /dev/null
+++ b/docs/scripts/checkNav.mjs
@@ -0,0 +1,54 @@
+#!/usr/bin/env node
+
+import fs from 'fs';
+import path from 'path';
+import { fileURLToPath, pathToFileURL } from 'url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+const navPath = '../docs/nav.mjs';
+
+const mdListPath = process.argv[2];
+if (!mdListPath) {
+    console.error('Usage: node checkNav.mjs <md-list-file>');
+    process.exit(1);
+}
+
+const navFile = path.resolve(__dirname, navPath);
+const nav = await import(pathToFileURL(navFile).href).then(mod => mod.default);
+
+const extractPathsFromNav = (items) =>
+    items.filter(item => item.type === 'page').map(page => page.path);
+
+const navPaths = extractPathsFromNav(nav.items);
+const navPathSet = new Set(navPaths);
+
+const expectedMdPaths = fs.readFileSync(path.resolve(__dirname, mdListPath), 'utf8')
+    .split('\n')
+    .map(line => line.trim())
+    .filter(Boolean);
+const expectedPathSet = new Set(expectedMdPaths);
+
+const missingInNav = expectedMdPaths.filter(p => !navPathSet.has(p));
+const extraInNav = navPaths.filter(p => !expectedPathSet.has(p));
+
+let failed = false;
+
+if (missingInNav.length > 0) {
+    console.error('❌ These docs are missing from nav:');
+    missingInNav.forEach(p => console.error(`- ${p}`));
+    failed = true;
+}
+
+if (extraInNav.length > 0) {
+    console.error('❌ These docs are listed in nav but not found under docs/:');
+    extraInNav.forEach(p => console.error(`- ${p}`));
+    failed = true;
+}
+
+if (!failed) {
+    console.log('✅ nav list matches filesystem.');
+} else {
+    process.exit(1);
+}