Fix "Error: listen EADDRINUSE: address already in use" in Node.js

What it means

Another process is already listening on that port, so your app can't. :::3000 means "port 3000 on all addresses". Most of the time the other process is an earlier copy of your own app.

• A dev server is still running in another terminal tab, or in the background after the terminal was closed.
• A watcher such as nodemon restarted the app before the old one finished exiting.
• Two projects are configured to use the same port.
• Another program uses that port, for example AirPlay Receiver on port 5000 on a Mac.

Fix 1: free the port

Find the process on the port and stop it. If it is an old copy of your app, that is all you need.

Get-NetTCPConnection -LocalPort 3000 -State Listen |
  ForEach-Object { Stop-Process -Id $_.OwningProcess }

kill $(lsof -t -iTCP:3000 -sTCP:LISTEN)

These stop whatever is on the port without asking. Detailed, step-by-step versions: Windows, macOS, Linux.

Fix 2: use another port

If the other program should keep running, start yours on a different port. Most frameworks read the PORT environment variable:

PORT=3001 npm start

$env:PORT=3001; npm start

Some tools use a flag instead: next dev -p 3001, vite --port 5174. See port already in use for React, Next.js and Vite.

Fix 3: a clear message instead of a stack trace

Handle the error in your server so the next person sees what to do:

const PORT = process.env.PORT || 3000;
const server = app.listen(PORT);

server.on('error', (err) => {
  if (err.code === 'EADDRINUSE') {
    console.error(`Port ${PORT} is already in use. Stop the other process or set PORT.`);
    process.exit(1);
  }
  throw err;
});

Stop it coming back

• Stop dev servers with Ctrl+C rather than closing the terminal window, which can leave them running.
• If it happens after every file save, the watcher is starting a new copy before the old one exits. Make sure the app closes its server on SIGTERM, or update nodemon.
• portfind shows which project each port belongs to, and warns when the same port keeps coming back after you kill it.