Port 4200: Angular dev server

What uses port 4200

ng serve starts the Angular development server on http://localhost:4200 with live reload. It is meant for development only; production Angular apps are built with ng build and served as static files.

Should port 4200 be open to the internet?

Keep private. Never expose this port to the internet. Keep it on localhost, a private network or behind a VPN or SSH tunnel.

• Run on another port with ng serve --port 4300, or make it reachable from other devices on your network with ng serve --host 0.0.0.0.

Check what is listening on port 4200

sudo ss -ltnp 'sport = :4200'

sudo lsof -nP -iTCP:4200 -sTCP:LISTEN

Get-NetTCPConnection -LocalPort 4200 -State Listen
netstat -ano | findstr :4200

No output means nothing is listening. If a service should be, check that it is running and which address it binds to: 127.0.0.1 only accepts local connections, 0.0.0.0 or :: accepts them on every interface.

Fix “address already in use” on port 4200

Another process already holds the port. Find it with the commands above, then stop that service properly, or end the process:

sudo kill $(sudo lsof -t -iTCP:4200 -sTCP:LISTEN)

Stop-Process -Id (Get-NetTCPConnection -LocalPort 4200 -State Listen).OwningProcess

Allow port 4200 from trusted networks only

The examples allow 4200 only from 10.0.0.0/8; replace it with your own private network, office IP or VPN range.

sudo ufw allow from 10.0.0.0/8 to any port 4200 proto tcp
# Close it again:
sudo ufw delete allow from 10.0.0.0/8 to any port 4200 proto tcp

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="10.0.0.0/8" port port="4200" protocol="tcp" accept'
sudo firewall-cmd --reload

New-NetFirewallRule -DisplayName "Angular dev server 4200/TCP" -Direction Inbound -Protocol TCP -LocalPort 4200 -Action Allow -RemoteAddress 10.0.0.0/8

On AWS, Google Cloud and Azure, also allow the port in the security group or network firewall rules; host firewalls and cloud firewalls are separate.

Test port 4200 from another machine

nc -zv example.com 4200

Test-NetConnection example.com -Port 4200

Related ports

• Port 3000 (Development server / Grafana): the default port of many development servers and of Grafana.
• Port 5173 (Vite dev server): the default port of the Vite development server.
• Port 8080 (HTTP alternate): the most common alternate HTTP port, used by proxies, app servers and dev tools.

More development servers ports

5000 (Flask / development servers) , 8000 (Development server (Django, Python)) , 8888 (Jupyter) , 9000 (PHP-FPM / MinIO / SonarQube) , 9418 (Git protocol) . See all ports in the port lookup.

Sources

• IANA port registry (not registered for this use)

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Frequently asked questions