Fix TimeoutError: API resolved without sending a response for /api/users, this may result in stalled requests in Next.js

This warning appears when a Next.js API route finishes execution without calling res.status().json() or res.end(). This typically happens when an async operation completes but the response is never sent, or when early returns skip the response. Fix it by ensuring every code path sends a response.

Reading the Stack Trace

Here's what each line means:

• at apiResolver (/app/node_modules/next/dist/server/api-utils/node.js:372:15): The API resolver detected that the handler function returned without sending a response to the client.
• at async DevServer.runApi (/app/node_modules/next/dist/server/next-server.js:487:9): The Next.js dev server invoked the API route and is now warning that the request may stall.
• at async Router.execute (/app/node_modules/next/dist/server/router.js:247:36): The internal router finished executing the matched API route handler.

Common Causes

export default async function handler(req, res) {
  const users = await db.query('SELECT * FROM users');
  // Forgot to send the response
}

export default async function handler(req, res) {
  if (req.method === 'POST') {
    const user = await createUser(req.body);
    return res.status(201).json(user);
  }
  // GET and other methods never send a response
}

export default async function handler(req, res) {
  try {
    const data = await fetchData();
    res.status(200).json(data);
  } catch (error) {
    console.error(error);
    // No response sent in catch block
  }
}

The Fix

Ensure every possible code path sends a response. Add explicit handlers for each HTTP method and a fallback 405 response for unsupported methods so no request is left without a response.

export default async function handler(req, res) {
  if (req.method === 'POST') {
    const user = await createUser(req.body);
    return res.status(201).json(user);
  }
  // GET never sends a response
}

export default async function handler(req, res) {
  if (req.method === 'POST') {
    const user = await createUser(req.body);
    return res.status(201).json(user);
  }

  if (req.method === 'GET') {
    const users = await getUsers();
    return res.status(200).json(users);
  }

  return res.status(405).json({ error: 'Method not allowed' });
}

Testing the Fix

import { createMocks } from 'node-mocks-http';
import handler from '@/pages/api/users';

describe('/api/users', () => {
  it('returns 200 and users for GET', async () => {
    const { req, res } = createMocks({ method: 'GET' });
    await handler(req, res);
    expect(res._getStatusCode()).toBe(200);
    expect(JSON.parse(res._getData())).toBeInstanceOf(Array);
  });

  it('returns 201 and created user for POST', async () => {
    const { req, res } = createMocks({ method: 'POST', body: { name: 'Alice' } });
    await handler(req, res);
    expect(res._getStatusCode()).toBe(201);
  });

  it('returns 405 for unsupported methods', async () => {
    const { req, res } = createMocks({ method: 'DELETE' });
    await handler(req, res);
    expect(res._getStatusCode()).toBe(405);
  });
});

Run your tests:

npm test

Pushing Through CI/CD

git checkout -b fix/api-route-missing-response,git add src/pages/api/users.ts src/pages/api/__tests__/users.test.ts,git commit -m "fix: ensure all API route code paths send a response",git push origin fix/api-route-missing-response

Your CI config should look something like this:

name: CI
on:
  pull_request:
    branches: [main]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'npm'
      - run: npm ci
      - run: npm test -- --coverage
      - run: npm run build

The Full Manual Process: 18 Steps

Here's every step you just went through to fix this one bug:

1. Notice the error alert or see it in your monitoring tool
2. Open the error dashboard and read the stack trace
3. Identify the file and line number from the stack trace
4. Open your IDE and navigate to the file
5. Read the surrounding code to understand context
6. Reproduce the error locally
7. Identify the root cause
8. Write the fix
9. Run the test suite locally
10. Fix any failing tests
11. Write new tests covering the edge case
12. Run the full test suite again
13. Create a new git branch
14. Commit and push your changes
15. Open a pull request
16. Wait for code review
17. Merge and deploy to production
18. Monitor production to confirm the error is resolved

Total time: 30-60 minutes. For one bug.

npm install bugstack-sdk

import { initBugStack } from 'bugstack-sdk'

initBugStack({ apiKey: process.env.BUGSTACK_API_KEY })

Deploying the Fix (Manual Path)

1. Run the test suite locally to confirm all API methods respond correctly.
2. Open a pull request with the API route fix.
3. Wait for CI checks to pass on the PR.
4. Have a teammate review and approve the PR.
5. Merge to main and verify the API routes work in staging.

Frequently Asked Questions