Have you had this problem before? You have started a service listening on some TCP port, and you want to know if it is reachable from the Internet, or if some firewall along the way are blocking the packets. Maybe you’re running the service yourself and testing it from your local network doesn’t tell you anything about reachability from the Internet?
Whatever the reason is for testing whether or not a TCP port is open from the Internet, here’s a service that can help you do just that: https://portchecker.bytopia.dk/
It’s really simple to use. Just enter an IP address (IPv4 or IPv6) and a TCP port number and click Check, and the service will tell you if the port is open or closed when accessing it from the Internet.