localhost:8081: what runs on it and how to open it
Port 8081 is used by the React Native Metro bundler and the Expo dev server. How to open it and fix errors.
Open this address: http://localhost:8081This opens on your own computer. It only works if the program is running.
localhost:8081 is the Metro bundler, the program that builds and serves your JavaScript to a React Native or Expo app. A phone or emulator connects to it, so errors usually mean the device cannot reach your computer.
What runs on localhost:8081
- React Native Metro bundler with
npx react-native start - Expo dev server with
npx expo start
Commands to start and test port 8081
npx react-native startnpx expo startcurl http://localhost:8081/statusadb reverse tcp:8081 tcp:8081Find what is using port 8081
Run these in a terminal on your computer. Nothing is sent to this site.
If localhost:8081 will not open
- Unable to load script / Could not connect to development server
- The app on the device cannot reach Metro. Keep the phone on the same Wi-Fi as your computer, or for Android over USB run
adb reverse tcp:8081 tcp:8081. - Port 8081 is already in use
- Another program is on port 8081. Find it with the tool below and stop it, or start yours on another port.
- This site can’t be reached (ERR_CONNECTION_REFUSED)
- The server is not running. Start it and keep that terminal open. See the full checklist.
- Works on your computer, not on your phone
- Start the server on all network addresses and use your computer’s IP address. See how to open localhost from your phone.
Other ports like 8081
| Port | Usually used by |
|---|---|
| localhost:3000 | React, Next.js, Express |
| localhost:5173 | Vite dev server |
| localhost:4200 | Angular dev server |
| localhost:5000 | Flask |
| localhost:8000 | Django, PHP, Python |
| localhost:8080 | Tomcat, Spring Boot, Docker |
| localhost:8888 | Jupyter Notebook |
Questions about localhost:8081
- Why does opening localhost:8081 show a plain page?
- Metro is a bundler, not a website. The page mostly confirms it is running, and the app loads its files from it.
- How do I check that Metro is running?
- Open localhost:8081/status. A running Metro answers packager-status:running.
- Is localhost:8081 safe?
- Yes, as long as it stays on localhost. Only your own computer can reach localhost:8081. It becomes reachable from other devices only if you start the program on 0.0.0.0 or your computer's IP address. Development servers are for testing, so do not put them on the public internet.
- Can I use a different port instead of 8081?
- Yes. Most programs let you choose the port with a setting or a command option. Pick a free port above 1024 and open that number instead, for example localhost:8082.
- How do I check what is using port 8081?
- Use the port checker on this page. It shows the command for Windows, macOS and Linux and does not send anything to this site.
- Can I open localhost:8081 from my phone?
- Yes, if both are on the same Wi-Fi. Start the program so it listens on all addresses, then open your computer's IP address with :8081 on the phone. A firewall on the computer can still block it.
Free tools that help
- Common ports listSearch a list of common TCP and UDP port numbers: SSH 22, HTTP 80, HTTPS 443, MySQL 3306, PostgreSQL 5432 and more, with dev server ports.