Port 8081 (Metro, alt HTTP)
Port 8081 is the default of Metro, the JavaScript bundler behind React Native and Expo, and a common second alternative HTTP port after 8080. IANA registers it for Sun Proxy Admin Service.
- Service
- Metro, alt HTTP
- Protocol
- TCP
- IANA registry
- Assigned to a different service: sunproxyadmin (Sun Proxy Admin Service), TCP/UDP. The use described here is not registered.
- Commonly used by
Check if a port is open on your IP
We only check the address you are visiting from, one TCP port at a time. You cannot enter someone else’s address: this is not a port scanner.
Is it safe to open port 8081?
Whatever runs on 8081 is usually a development or admin service, not a public site. Check what listens there (commands below) and keep it off the internet unless it has its own login and TLS.
“Port 8081 is already in use”: how to fix it
The error means another program is already listening on port 8081. Find its process ID (PID), then stop that program or start yours on a different port.
Windows (Command Prompt or PowerShell as administrator)
netstat -ano | findstr :8081taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:8081 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :8081sudo lsof -i :8081sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Why a port can look closed when your server is running
Most home networks sit behind a router doing NAT: the router owns the public address, and your computer has a private one such as 192.168.1.10. A connection from the internet reaches the router and stops there unless you add a port forwarding rule to your computer.
Many mobile and some home providers go further and use carrier-grade NAT (CGNAT): several customers share one public address, and your router itself gets an address from 100.64.0.0/10. Then no rule on your side can open a port; ask the provider for a public IP or use a tunnel or VPN service.
Even with forwarding in place, the firewall on the computer (Windows Defender Firewall, ufw, firewalld) must allow the port, and the program must listen on all interfaces (0.0.0.0), not only on 127.0.0.1.
UDP cannot be checked this way: a UDP service usually stays silent to packets it does not understand, so “no answer” means nothing. This check uses TCP only.
Frequently asked questions
What is port 8081 used for?
Port 8081 is the default of Metro, the JavaScript bundler behind React Native and Expo, and a common second alternative HTTP port after 8080. IANA registers it for Sun Proxy Admin Service.
Is port 8081 TCP or UDP?
Port 8081 uses TCP. This use is not registered with IANA.
Is it safe to open port 8081?
Whatever runs on 8081 is usually a development or admin service, not a public site. Check what listens there (commands below) and keep it off the internet unless it has its own login and TLS.
How do I free port 8081 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :8081 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :8081 and stop it with kill <pid>.