Hi all,
I created a tool that you can use to test that your GE:S (or other Source-based) game server is reachable from the internet. Great for verifying port forwarding and firewall configuration!
Try it here: https://www.geshl2.com/server-test/It will check if the specified TCP and UDP port is reachable and display the result. It always queries the IP address of the requestor.
If you need to test from a server that doesn't have a GUI, there's also a version that only outputs plain-text responses.