universal-modder

Skills, tools and a shared knowledge base that let any AI coding agent mod almost any PC game you own. The agent finds the game, works out the engine and the route, reads the real code, builds the mod, makes art, 3D and sound with fal, tests it in the running game, cuts the video, and writes down what it learned for the next agent.

Coming next: the mod hub. Publish your mods, remix other people's, and make new ones.

Install

Pick your agent. Each gets the same skills (Agent Skills format), the fal MCP server, and the um CLI.

Agent	Install
Claude Code	/plugin marketplace add rehan-remade/universal-modder``/plugin install universal-modder@universal-modder
Codex	codex plugin marketplace add rehan-remade/universal-modder``codex plugin add universal-modder@universal-modder
Gemini CLI	gemini extensions install https://github.com/rehan-remade/universal-modder
VS Code / Copilot	Enable chat.plugins.enabled, run Chat: Install Plugin From Source, and enter this repo's URL
Cursor	Cursor Marketplace, or clone (Cursor reads AGENTS.md and .cursor/mcp.json)
OpenCode	Clone and run opencode inside it (opencode.json adds the skills and the fal MCP server)
Skills only(any agent)	npx skills add https://github.com/rehan-remade/universal-modder
Anything else	git clone https://github.com/rehan-remade/universal-modder and start your agent inside it

Inside a clone, each agent finds the skills where it looks for them: .agents/skills (Codex, Gemini CLI, Copilot, Cursor, OpenCode) and .claude/skills (Claude Code) are copies of skills/. Instructions are in AGENTS.md, which CLAUDE.md and GEMINI.md point to. MCP config is in .mcp.json, .codex/config.toml, .cursor/mcp.json, .vscode/mcp.json and opencode.json (which also points OpenCode at skills/).

The um CLI. Plugin installs and clones put it on PATH. Anywhere else:

uv tool install git+https://github.com/rehan-remade/universal-modder     # or: pipx install git+...

For assets, get a fal API key. It powers both the fal MCP server and um fal (for images without a key, um comfy uses a local ComfyUI server):

export FAL_KEY=...

You also need Git, Python 3.10+ and ffmpeg. uv is recommended. Blender is needed for 3D → sprite renders. Windows games are driven natively or from WSL.

Try it

Mod Terraria: add a homing missile launcher and a tactical nuke that craters the world. Make the sprites with fal.

Make a new civilization for Age of Empires II with a unique unit rendered from 3D.

Put real Minecraft inside GTA V story mode. Minecraft's camera should follow GTA's, and its TNT should blow up GTA cars.

Port the Warthog from my Halo install into Minecraft, with a gunner on the turret.

What engine is C:\Games\Foo, and has anyone modded it before?

The agent starts with the mod-any-game skill and runs the same loop every time:

1. search the knowledge base;
2. recon, then pick a route;
3. set up a safe lab (saves backed up);
4. read the actual code;
5. build one working slice;
6. generate assets;
7. verify in the real game;
8. record;
9. package;
10. write a field note for the next agent.

A knowledge base that AIs write for AIs

knowledge/ holds field notes: how specific games were actually modded, decompiled and reverse-engineered. Each note gives:

• the exact versions that worked;
• the route, and why;
• what the engine really does;
• how it was verified;
• the gotchas (symptom → cause → fix).

Every agent that finishes a mod can open a pull request with its note, so the next agent starts where it left off instead of rediscovering the same traps.

um kb search "grand theft auto"                 # before you start: prior art (works outside the repo too)
um kb new --game "Hades II" --title "A new boon god" --from-scan hades --agent "Codex (gpt-6)"
um kb check knowledge/games/hades-ii/a-new-boon-god.md
um kb pr knowledge/games/hades-ii/a-new-boon-god.md --yes    # after your human says OK: branch, push, PR

Browse knowledge/INDEX.md. Every game is welcome. Contribution rules, for humans and AIs, are in CONTRIBUTING.md: no game files, no decompiled dumps, no cheating other players, and an honest status and verification.

A few notes from the community:

• Portalcraft: real Minecraft inside Portal 2
• Halo 3 weapons, Covenant, vehicles and maps ported into Minecraft
• Bloons TD 6 inside Minecraft, with the game's rules as a headless sim
• A CS2-style conversion of Elden Ring offline, as a native Rust DLL

What's inside

Skills (skills/, Agent Skills format)

SkillWhat it does