diff --git a/sample-app/src/app.test.ts b/sample-app/src/app.test.ts
index c2d8dfe..d7263fd 100644
--- a/sample-app/src/app.test.ts
+++ b/sample-app/src/app.test.ts
@@ -39,4 +39,37 @@ describe('Task API', () => {
     const res = await request(createApp()).get('/tasks/does-not-exist');
     expect(res.status).toBe(404);
   });
+
+  it('rejects a missing title with 400 and does not create a task', async () => {
+    const app = createApp();
+
+    const res = await request(app).post('/tasks').send({});
+    expect(res.status).toBe(400);
+    expect(res.body.error).toBeTruthy();
+
+    const list = await request(app).get('/tasks');
+    expect(list.body).toHaveLength(0);
+  });
+
+  it('rejects a non-string title with 400 and does not create a task', async () => {
+    const app = createApp();
+
+    const res = await request(app).post('/tasks').send({ title: 42 });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toBeTruthy();
+
+    const list = await request(app).get('/tasks');
+    expect(list.body).toHaveLength(0);
+  });
+
+  it('rejects a whitespace-only title with 400 and does not create a task', async () => {
+    const app = createApp();
+
+    const res = await request(app).post('/tasks').send({ title: '   ' });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toBeTruthy();
+
+    const list = await request(app).get('/tasks');
+    expect(list.body).toHaveLength(0);
+  });
 });
diff --git a/sample-app/src/tasks/routes.ts b/sample-app/src/tasks/routes.ts
index e3eabca..9d4f799 100644
--- a/sample-app/src/tasks/routes.ts
+++ b/sample-app/src/tasks/routes.ts
@@ -10,9 +10,12 @@ export function createTaskRouter(store: TaskStore): Router {
   });
 
   router.post('/', (req, res) => {
-    // Exercise 1: validate that req.body.title is a non-empty string and
-    // return 400 with a helpful message when it is not.
     const { title } = req.body ?? {};
+    if (typeof title !== 'string' || title.trim() === '') {
+      return res.status(400).json({
+        error: 'title is required and must be a non-empty string',
+      });
+    }
     const task = store.create(title);
     res.status(201).json(task);
   });