Guide: Fix API resolved without sending a response for /api/ in Next.js

The warning API resolved without sending a response for /api/... in Next.js occurs when an API Route Handler or Pages API endpoint executes asynchronous logic (such as database queries, third-party APIs, or webhooks) without await or without resolving a returned Promise before the handler function finishes execution.

This issue can cause Node.js server connections to hang, resulting in frontend request timeouts, memory leaks, and dropped HTTP responses.

Step-by-Step Solution

Ensure proper async/await flow in your handler If you are using the Pages Router (pages/api/...), every asynchronous database call must be completed before returning the response:

// pages/api/users.js
export default async function handler(req, res) {
  try {
    // Omitting await will trigger the unhandled resolution warning
    const users = await db.collection('users').find().toArray();
    return res.status(200).json({ success: true, data: users });
  } catch (error) {
    return res.status(500).json({ success: false, error: error.message });
  }
}

Wrap callback-based libraries inside Promises When dealing with older packages that do not provide native Promises (e.g. jsonwebtoken or multer), explicitly wrap the call:

export default async function handler(req, res) {
  await new Promise((resolve) => {
    jwt.verify(token, secretKey, (err, decoded) => {
      if (err) {
        res.status(401).json({ error: 'Invalid token' });
        return resolve();
      }
      res.status(200).json({ user: decoded });
      return resolve();
    });
  });
}

Use App Router Route Handlers (Next.js 13+) For the modern App Router (app/api/.../route.js), return native web standard Response or NextResponse instances:

// app/api/users/route.js
import { NextResponse } from 'next/server';

export async function GET(request) {
  const data = await fetchUserData();
  return NextResponse.json(data);
}