How port checking works
Every internet service listens on a numbered port: web servers on 80 and 443, SSH on 22, and so on. This tool attempts a connection to the port you choose. A successful connection means the port is open and something is listening. A timeout means it's closed or filtered by a firewall.
Common ports
- 80 / 443: web traffic (HTTP / HTTPS).
- 22: SSH remote access.
- 25: email (SMTP).
- 3389: Windows Remote Desktop.
Curious about carrier-grade NAT, which can stop port forwarding working at all? Read what CGNAT is.
Frequently asked questions
What does this port checker do?
It tries to open a TCP connection to the host and port you enter. If the connection succeeds, the port is open and reachable from the internet. If it times out, the port is closed or a firewall is blocking it.
Why is my port closed?
Home routers block incoming connections by default for security. To open one you'd set up port forwarding on your router, and your ISP must not be using carrier-grade NAT.
Is leaving ports closed a good thing?
Yes. Closed incoming ports are normal and safer for home users. Only open a port when a specific app, like a game server, needs it.