Fix Port Already in Use Error Instantly

If you see an error like "Port 3000 is already in use", it means another process is using that port.

On Mac or Linux, run:
lsof -i :3000

This will show the process ID (PID). Then kill it:
kill -9 <PID>

On Windows, run:
netstat -ano | findstr :3000

Then kill the process:
taskkill /PID <PID> /F

Alternatively, you can start your app on a different port:
PORT=3001 npm start

This issue usually happens when a previous server process did not shut down properly. Always stop your server cleanly using Ctrl + C.