sigfai/universal-modder

Install

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

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 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)

The um CLI (Python). Every command has --help with examples.

Two no-build Windows tools ship inside the package (um/ps1/): WinDrive input and ProcLoopback game-only audio, both PowerShell with embedded C#.

Built with it

• examples/terraria-tmodloader: Fal Arsenal for tModLoader.
  • Weapons: a homing missile launcher, a tactical nuke (crater + mushroom cloud), a chain-lightning rifle, a black-hole gun and an orbital strike.
  • Three new enemies and a two-phase Drone Mothership boss.
  • Every sprite came from fal.
• examples/aoe2-de-civ: San Franciscans for Age of Empires II DE.
  • A new civilization with a Robotaxi unique unit and Delivery Drones, rendered from fal image-to-3D models at AoE2's camera angle.
  • A Transamerica Pyramid wonder.
  • A reverse-engineered .sld sprite writer.
• examples/minecraft-gta5-passthrough: real Minecraft inside GTA V story mode.
  • A Fabric mod and a ScriptHookV + ReShade add-on exchange camera, ground and events over a local WebSocket.
  • Minecraft's colour + depth are depth-composited into GTA's frame.
  • Minecraft TNT, arrows and fireworks become GTA explosions and bullets, and Minecraft mobs fight the police.

Each has a field note with every non-obvious lesson: knowledge/INDEX.md.

Rules it follows

• Any game you own: single-player, multiplayer, or servers you host. It refuses to inject into online games with anti-cheat, write cheats against other players, or bypass anti-cheat, DRM or ownership checks.
• It never ships game files or decompiled code. Mods ship as code, your own assets, patches or converters.
• It backs up before touching saves, and kills processes by PID only.
• It asks before driving your mouse and keyboard, installing loaders into game folders, or publishing, PRs included.

Full reasoning: skills/mod-any-game/references/safety.md.

Made a mod with it?

Put the badge on your mod's page:

[![made with universal-modder](https://raw.githubusercontent.com/rehan-remade/universal-modder/main/docs/media/made-with-dark.svg)](https://github.com/rehan-remade/universal-modder)

Use made-with-light.svg on a light page.

Credits

• Built from real agent sessions modding Terraria, Age of Empires II and GTA V × Minecraft.
• Assets: fal (GPT Image 2, Nano Banana 2, FLUX, Trellis 2, ElevenLabs...).
• Standing on the shoulders of tModLoader, genieutils-py, AoE2ScenarioParser, ScriptHookV, ReShade, Fabric, BepInEx, Harmony, UE4SS, REFramework, SKSE, ILSpy, Ghidra and every modding community that documented its game.
• The engine playbooks also draw on the September 2026 wave of AI-built mods, and on how their creators explained them in public.

MIT licensed. Brand type: Geist Pixel, Sometype Mono and Instrument Sans. Video titles: Space Grotesk and JetBrains Mono. All under the SIL OFL.

Star history