What it does
CanYouSeeMe checks whether an externally addressed port can be reached and explains the relationship between router forwarding and private devices.
Use the displayed external IP and the port assigned to the service when checking access from outside the LAN. CanYouSeeMe explains the usual NAT arrangement: the router holds the public address, while the server has a private address that cannot be reached directly from the Internet. A forwarding rule directs the chosen port toward that service. The free checker supplies a remote reachability observation for that address and port. If it fails, investigate the running service, forwarding rule, firewall and provider path rather than assuming one of them is the cause. A successful check also does not validate every application function.