Port 4200 ANGULAR CLI
Port 4200 is the community default for Angular CLI, using TCP.
What is port 4200 used for?
Port 4200 is widely used by Angular CLI (TCP), a community convention rather than an IANA assignment. Default development server port for Angular CLI projects. It sits in the registered range, the block used by databases, application servers and developer tooling. Port conflicts here are common when several local services start at once.
Ports are the transport-layer address a service listens on. A client that wants to reach Angular CLI connects to port 4200. If nothing is listening, the connection is refused. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 4200 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Because this number is not IANA-assigned, a different application may legitimately use it on a machine you do not control. Always identify the actual listening process before deciding that the port belongs to this technology.
Browse all Development servers ports
This port number is not assigned by IANA. The entry documents a widely adopted community convention.
Check and block port 4200
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :4200'Check on Windows
Get-NetTCPConnection -LocalPort 4200 -State Listen -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 4200/tcpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 4200 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 4200 safe to expose?
Angular CLI's dev server is intended for local development only; it should not be exposed to the public internet. Expose this port only when the service is actually needed. Keep it patched, prefer an encrypted alternative, and limit source addresses with a firewall allowlist.
Where port 4200 is usually used
Most traffic on port 4200 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Starting a framework development server and opening the localhost URL it prints.
- Testing a frontend against a local API, proxy or mock service.
- Hot-reload sessions that should stay bound to 127.0.0.1 instead of a public interface.
Start the Angular dev server
Angular CLI serves the app on 4200 by default; open the printed localhost URL when it starts.
ng serve --port 4200Common problems with port 4200
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 4200. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :4200' or sudo lsof -i :4200. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 4200 at a glance
| Port number | 4200 |
|---|---|
| Service name | Angular CLI |
| Transport protocol | TCP |
| Category | Development servers |
| Range | Registered port (1024–10000) |
| Risk level | Medium |
| Reference | Community convention (not IANA-assigned) |
| Registry description | Default development server port for Angular CLI projects |
| Source | Community convention |
Frequently asked questions
What is port 4200 used for?
Port 4200 (ANGULAR CLI) uses TCP. Default development server port for Angular CLI projects (community convention, not an IANA assignment).
How do I check if port 4200 is open?
On Linux run `sudo ss -tlpn 'sport = :4200'`. On Windows run `Get-NetTCPConnection -LocalPort 4200 -State Listen -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 4200; empty output usually means nothing is bound to it.
How do I block port 4200?
With UFW run `sudo ufw deny 4200/tcp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 4200 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 4200 safe to expose?
Angular CLI's dev server is intended for local development only; it should not be exposed to the public internet. Nevertheless, expose this port only when the service is actually needed. Keep it patched, prefer an encrypted alternative, and limit source addresses with a firewall allowlist.
Related ports
Primary data: IANA Service Name and Transport Protocol Port Number Registry. This number is a community convention, not an IANA assignment.
Last reviewed 2026-10-30 · Methodology · About · Privacy