What port does a Garry's Mod server use?

27015 by default, UDP and TCP, for game traffic, pings and RCON. Change it with -port.

Do I need a GSLT for a Garry's Mod server?

The Garry's Mod wiki calls it mandatory: servers without sv_setsteamaccount are ranked lower in the server browser.

Why isn't my GMod server in the server browser?

Check hide_server is 0, add a GSLT, and forward 27015. Friends can always use connect IP:27015 in the console.

Can I host a Garry's Mod server without port forwarding?

Yes: start the dedicated server with -p2p. It prints how players can connect.

What is the Garry's Mod dedicated server app ID?

4020, installed with SteamCMD and anonymous login.

Garry's Mod server: friends can't join or not listed? Fix

Quick answer

A Garry's Mod dedicated server (srcds) uses port 27015 for game traffic, pings and RCON (UDP and TCP; change it with -port). If friends can't join, forward 27015 to the server PC and allow srcds through the firewall. If the server doesn't show in the browser, check hide_server and set a GSLT with +sv_setsteamaccount <token>: the Garry's Mod wiki calls the token mandatory and ranks servers without one lower. Behind CGNAT, the server's -p2p mode lets players connect without port forwarding.

Ports

27015 UDP + TCP: Game traffic, pings (Steam query) and RCON. Set with -port
27005 UDP: Client port (-clientport)
27020 UDP: SourceTV (+tv_port), only if you use it

How to fix it, step by step

Install and start the server. Install with SteamCMD (app_update 4020 validate), then run srcds.exe -console +maxplayers 20 +gamemode sandbox +map gm_construct. On Linux: ./srcds_run -game garrysmod +maxplayers 32 +map gm_construct.
Add a GSLT. Create a token at steamcommunity.com/dev/managegameservers and add +sv_setsteamaccount <token> to the launch line. The wiki says it's mandatory and servers without it are ranked lower in the browser.
Forward 27015. Reserve the server PC's local IP and forward 27015 UDP and TCP to it. If you used -port, forward that port and share IP:port.
Allow srcds through the firewall. Allow srcds.exe on Private and Public networks in Windows Firewall, or open 27015 on Linux.
Make it visible. Check hide_server isn't 1. Set sv_location (for example sv_location us) so the right flag shows.
Test from outside. Have a friend open the console and connect your-public-ip:27015. Joining your own public IP from inside your network can fail even when the forward works. If outside joins time out, check for CGNAT (see the CGNAT guide).

Hosting without port forwarding

The Garry's Mod wiki notes that a dedicated server can run in peer-to-peer mode with the -p2p launch option. On startup the server prints how players can connect to it manually. Useful behind CGNAT.

Workshop content

Add +host_workshop_collection <collectionID> to the launch line so the server installs a Workshop collection.

Test it from the outside

Your own Wi-Fi can't tell you whether friends can reach the server. The free Server Doctor check contacts your server once from the internet, the way the game does, and tells you the most likely cause. The same check runs in Discord with /fix.

No PC to host 24/7?

A GMod server needs your PC on whenever people play. Behind CGNAT the browser can't reach it. A rented server keeps it online with a public IP.

Still stuck? Get free help from real people in our Discord

Post your game, where it runs and what the check said in #help-forum. Other server hosts and the Server Doctor team can take a look. Free.

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Garry's Mod server not showing up, or friends can't join?