What is Port Checker?
Port Checker is a simple and free online tool for checking open ports on your computer/device or servers, often useful in testing port forwarding settings on a router. For instance, if you're facing connection issues with a program (email, IM client etc) then it may be possible that the port required by the application is getting blocked by your router's firewall or your ISP.
In such cases, this tool might help you in diagnosing any problem with firewall setup. You could also find this useful for security purpose, in case you're not sure whether a particular port is open or closed.