: Tools like gmpublisher or GModPatchTool are used for legitimate mod management and patching. Security Warning

For a safe and official guide on how to automatically manage and download add-ons for your game, watch this tutorial:

Be cautious when downloading .zip files from unofficial sources with "Auto Updater" in the name. These are often used to distribute malware or pirated content. If you are looking for the official game, it is available on the Steam Store .

Are you trying to or looking for a way to play the game without Steam ?

: By default, Steam keeps Garry's Mod updated. If you need to stop this, you can set the game's manifest file ( appmanifest_4000.acf ) to "Read-only".