Did you mean to visit localhost:3000?
💡 Pro Tip: Port 3000 is the default for React and Express apps. If you get "port already in use" errors, try using PORT=3001 or kill the existing process.
Quick Commands for Port 3000
Find what's using port 3000:
lsof -i :3000 (Mac/Linux)
netstat -ano | findstr :3000 (Windows)
Kill the process:
kill -9 PID (Mac/Linux)
taskkill /PID PID /F (Windows)
About Port 3000
Port 3000 is commonly used by:
- React applications created with Create React App
- Node.js applications using Express.js
- Ruby on Rails development server
- Gatsby development server
Common Issues with Port 3000
"Port 3000 is already in use"
This error occurs when another application is already using port 3000. Solutions:
- Find and close the application using port 3000
- Use a different port by setting an environment variable:
- React:
PORT=3001 npm start
- Express: Change the port in your code
- On Windows, you can find and kill the process:
netstat -ano | findstr :3000 then taskkill /PID [PID] /F
✅ Quick Solution
Start React on a different port: PORT=3001 npm start
"Cannot connect to localhost:3000"
If your application is running but you can't connect:
- Check if your application is actually running
- Make sure you're not using HTTPS when the server is HTTP
- Try using 127.0.0.1:3000 instead of localhost:3000
- Check if a firewall is blocking the connection