diff --git a/scripts/data/blog.mjs b/scripts/data/blog.mjs
index 9c90fd4a..824faec1 100644
--- a/scripts/data/blog.mjs
+++ b/scripts/data/blog.mjs
@@ -11,6 +11,18 @@ const OUTPUT = join(ROOT, 'generated', 'blog.json');
 
 const titleFromBody = body => body.match(/^#\s+(.+)$/m)?.[1].trim() ?? null;
 
+const parseDate = (value, file) => {
+  const date = value ? new Date(value) : null;
+
+  if (!date || Number.isNaN(date.getTime())) {
+    throw new Error(
+      `Invalid or missing blog date in pages/blog/posts/${file}: ${JSON.stringify(value ?? '<missing>')}`
+    );
+  }
+
+  return date.toISOString();
+};
+
 const readPosts = async () => {
   const entries = await readdir(POSTS_DIR);
   const files = entries.filter(name => name.endsWith('.md'));
@@ -26,7 +38,7 @@ const readPosts = async () => {
         slug,
         title: titleFromBody(content) ?? slug,
         authors: data.authors?.split(',').map(s => s.trim()),
-        date: new Date(data.date).toISOString(),
+        date: parseDate(data.date, file),
         category: data.category ?? null,
         image: data.image ?? null,
         ...(data.description && { description: data.description }),
diff --git a/tests/data/blog.test.mjs b/tests/data/blog.test.mjs
new file mode 100644
index 00000000..bc5a0bf8
--- /dev/null
+++ b/tests/data/blog.test.mjs
@@ -0,0 +1,68 @@
+import { strict as assert } from 'node:assert';
+import { execFile } from 'node:child_process';
+import {
+  copyFile,
+  mkdtemp,
+  mkdir,
+  readFile,
+  rm,
+  writeFile,
+} from 'node:fs/promises';
+import { promisify } from 'node:util';
+import { fileURLToPath } from 'node:url';
+import { join } from 'node:path';
+import { test } from 'node:test';
+
+const execFileAsync = promisify(execFile);
+const blogScript = fileURLToPath(
+  new URL('../../scripts/data/blog.mjs', import.meta.url)
+);
+
+const createFixture = async content => {
+  const root = await mkdtemp(join('tests', 'data', '.blog-'));
+  await mkdir(join(root, 'scripts', 'data'), { recursive: true });
+  await mkdir(join(root, 'pages', 'blog', 'posts'), { recursive: true });
+  await mkdir(join(root, 'generated'), { recursive: true });
+  await copyFile(blogScript, join(root, 'scripts', 'data', 'blog.mjs'));
+  await writeFile(join(root, 'pages', 'blog', 'posts', 'example.md'), content);
+  return root;
+};
+
+const runFixture = root =>
+  execFileAsync(process.execPath, ['scripts/data/blog.mjs'], { cwd: root });
+
+test('generates blog data for valid dates', async t => {
+  const root = await createFixture("---\ndate: '2026-09-22'\n---\n# Test\n");
+  t.after(() => rm(root, { recursive: true, force: true }));
+
+  await runFixture(root);
+  const posts = JSON.parse(
+    await readFile(join(root, 'generated', 'blog.json'), 'utf8')
+  );
+
+  assert.equal(posts[0].date, '2026-09-22T00:00:00.000Z');
+});
+
+test('reports the file for an invalid blog date', async t => {
+  const root = await createFixture('---\ndate: not-a-date\n---\n# Test\n');
+  t.after(() => rm(root, { recursive: true, force: true }));
+
+  await assert.rejects(runFixture(root), error => {
+    assert.match(error.stderr, /Invalid or missing blog date/);
+    assert.match(error.stderr, /pages[\\/]blog[\\/]posts[\\/]example\.md/);
+    assert.match(error.stderr, /not-a-date/);
+    return true;
+  });
+});
+
+test('reports the file for a missing blog date', async t => {
+  const root = await createFixture('---\ntitle: Test\n---\n# Test\n');
+  t.after(() => rm(root, { recursive: true, force: true }));
+
+  await assert.rejects(runFixture(root), error => {
+    assert.match(error.stderr, /Invalid or missing blog date/);
+    assert.match(error.stderr, /pages[\\/]blog[\\/]posts[\\/]example\.md/);
+    assert.match(error.stderr, /<missing>/);
+    return true;
+  });
+});