Garry's Mod Modding on OpenMods

A sandbox game that is, fundamentally, a mod platform

Garry's Mod (2006) is harder to describe than most games because it isn't really a game, it's a Source engine sandbox where everything interesting is community-built. Maps, gamemodes (TTT, DarkRP, Murder, Sandbox itself), weapons, vehicles, NPCs: virtually every meaningful experience in Garry's Mod is a mod. Facepunch (the developers) provide the engine, the Workshop, and Lua bindings; the community provides the rest.

The result is one of the largest single-game modding scenes ever, with the Steam Workshop hosting hundreds of thousands of addons. Lua is the scripting language. Source SDK Hammer is the level editor.

The toolchain

• Steam Workshop: the central distribution channel. Subscribe in-browser or in-game.
• Source SDK / Hammer: Valve's level editor, also used by Garry's Mod.
• GMad: Garry's Mod addon packer, builds .gma archives.
• GMod 13 / GMod x64: current Garry's Mod build (x64 became standard in 2024).

Mods (called "addons") ship as .gma archives. Workshop subscriptions auto-download; manual installs drop into Garry's Mod/garrysmod/addons/.

What you'll find on OpenMods

Garry's Mod's mod community is overwhelmingly Workshop-based. GitHub hosts source for the larger community projects (TTT2, custom gamemodes, server-management tools). OpenMods catalogues GitHub-published GMod addons, typically gamemode framework code or server tooling rather than content addons.

Practical notes

• The "addon" vs "mod" distinction. In Garry's Mod, everything is an "addon": maps, models, gamemodes, scripts, vehicles. The term "mod" is reserved for engine-level changes (rare).
• Gamemodes are the structural unit. TTT, DarkRP, Sandbox, Prop Hunt, each is a separate gamemode with its own ruleset. Servers pick one gamemode at a time.
• Server addons vs client addons. Some addons (gamemodes, maps, server scripts) need to be installed on the server. Cosmetic addons (player models, weapon skins) run client-side and are auto-downloaded when joining a server.
• The x64 transition (2024) updated everything. Most popular addons were updated quickly. A few legacy addons remain 32-bit-only.