Factorio server status checker
Factorio is different from everything else here: the check does not talk to your server at all, it asks Factorio's own matchmaking service about it.
Which ports a Factorio server needs
Your server publishes itself to Factorio's public server list, and that listing is what gets read back. The consequence is that port forwarding is not what determines the result — visibility settings are. A server with `public_visibility` disabled, or without valid Factorio account credentials in its settings file, is invisible here even though it is running perfectly and accepting direct connections.
If it still shows offline
Check the visibility and credential settings in server-settings.json before touching your router. If you deliberately run a private server, this tool cannot see it by design — use the port tester instead to confirm the game port is reachable.