Open port checker: what this test checks
A TCP port is a numbered endpoint that software can use for network connections. A listening service may accept traffic on a particular port, such as HTTPS on 443 or a game server on its configured port. This open port checker asks the site's server to try one TCP connection to your public IP address, as seen by the site's connection, on the port you chose. It accepts no hostname or other target IP, so it cannot scan other people's computers.
Open means a TCP connection was accepted during the test. It does not identify the software or confirm that it is configured safely. Closed or filtered means the connection did not succeed before the short timeout. A firewall may discard the request without a reply, a router may lack a forwarding rule, the service may be stopped, or the operating system may reject the connection. From outside, the browser cannot tell these causes apart.
Why a home port may appear closed
To expose a device behind a home router, the service usually needs to listen on its local interface, and the router needs a matching port-forward rule. Both the router firewall and device firewall must allow the traffic. Check the service's port setting and confirm the device still uses the local address in the forwarding rule. Some routers cannot connect back to their public address from inside the same network. In that case, run the test from a phone on mobile data or another outside connection.
Carrier-grade NAT adds a router controlled by your internet provider. With CGNAT, your router may not own the public address shown here, so port forwarding on your router alone cannot create an inbound route. Double NAT can have the same effect when two routers are in series. Ask your provider about assigning a public IPv4 address, or use a supported IPv6 firewall rule. Our port-forwarding guide and CGNAT explanation cover these layouts.
How to use an open port check safely
Check only ports for services you administer. A positive result means the port is reachable. Confirm the service uses authentication, current software, and only the access it needs. A negative result is not a security audit. It says nothing about UDP, other ports, internal network exposure, or service vulnerabilities. This is a momentary check from one network location, and provider or firewall rules may change the result later.
Frequently asked questions
Which public IP does this tool test?
The site's server uses the source address from your HTTP connection. No destination address is accepted in the form.
Why does my port check fail when forwarding is configured?
The service may not be listening, a firewall may block it, the device address may have changed, or CGNAT/double NAT may prevent inbound traffic.
Does it test UDP?
No. It attempts one TCP connection only. UDP has no equivalent connection handshake and is not checked here.
Does the endpoint keep my address?
The server uses the request source address for the connection attempt and does not save the result or address; standard hosting logs may apply.
More free tools: IP lookup · Blacklist check · WebRTC test · Speed test