Port 3000 Already in Use: Fixes for Windows, Mac, and Linux

Find the process using port 3000:

lsof -i :3000

This shows the process name and PID (process ID). Kill it:

kill -9 <PID>

Or do it in one step:

fuser -k 3000/tcp

If lsof is not installed (common on minimal server images), use ss instead:

ss -tlnp | grep 3000

The commands are the same as Linux. macOS ships with lsof:

lsof -i :3000
kill -9 <PID>

On macOS Monterey and later, the AirPlay Receiver service sometimes grabs port 5000. If your app uses port 5000 and you see this conflict, disable AirPlay Receiver in System Settings > General > AirDrop & Handoff.

Open Command Prompt or PowerShell as Administrator.

Find the process:

netstat -ano | findstr :3000

The last column is the PID. Kill it:

taskkill /PID <PID> /F

In PowerShell, you can also use:

Get-Process -Id (Get-NetTCPConnection -LocalPort 3000).OwningProcess | Stop-Process -Force

If you do not want to kill the existing process, start your app on a different port instead.

Next.js:

npx next dev -p 3001

Or set it in your package.json scripts:

"dev": "next dev -p 3001"

Express:

const PORT = process.env.PORT || 3001;
app.listen(PORT);

Vite:

npx vite --port 3001

Django:

python manage.py runserver 3001

Using an environment variable for the port (process.env.PORT) is the most flexible approach because deployment platforms set this variable automatically.

The most common cause is a previous dev server that did not shut down cleanly. If you close a terminal window without stopping the server (Ctrl+C), the process keeps running in the background.

Good habits:

• Always stop servers with Ctrl+C before closing the terminal.
• If your dev server crashes, check if it left a zombie process before restarting.
• Some frameworks (Next.js, Vite) detect the port conflict and offer to use the next available port automatically. Accept the prompt when it appears.