Skills, tools and the fal MCP that let Claude Code mod almost any PC game you own.
It finds the game, works out the engine and the modding route, reads the real code, builds the mod,
generates art, 3D and sound with fal, tests it in the running game, and cuts the showcase video.

Install

As a Claude Code plugin (recommended):

/plugin marketplace add rehan-remade/universal-modder
/plugin install universal-modder@universal-modder

Or clone it and run Claude inside it (works with Codex/Cursor via AGENTS.md too):

git clone https://github.com/rehan-remade/universal-modder && cd universal-modder && claude

Then give it a fal API key for assets. It powers both the bundled fal MCP server and the um fal CLI:

export FAL_KEY=...

You also need Python 3.10+ and ffmpeg. uv is recommended; the CLI sets up its own env with it. 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.

I own Skyrim SE. What would it take to put a Minecraft-style block-building mode in it?

What engine is C:\Games\Foo, and how do people mod it?

Claude starts with the mod-any-game skill and runs the same loop every time: recon, pick a route, set up a safe lab (saves backed up), read the actual code, build one working slice, generate assets, verify in the real game, record, then package.

What's inside

Skills (skills/)

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

Also bundled: the fal MCP server (.mcp.json), a SessionStart hook that puts um on PATH, and two no-build Windows tools in tools/win/: WinDrive input and ProcLoopback game-only audio, both PowerShell with embedded C#.

Built with it

• examples/terraria-tmodloader: Fal Arsenal for tModLoader. A homing missile launcher, a tactical nuke (crater + mushroom cloud), a chain-lightning rifle, a black-hole gun, 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.

Both started as one-line prompts. The non-obvious lessons from each are written into the skills (skills/mod-any-game/references/case-studies.md).

Rules it follows

• Single-player and offline, on games you own. It refuses to inject into online games with anti-cheat, write multiplayer cheats, 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.

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

Credits

• Built from real sessions of Claude Code modding Terraria and Age of Empires II.
• Assets: fal (GPT Image 2, Nano Banana 2, FLUX, Trellis 2, ElevenLabs...).
• Standing on the shoulders of tModLoader, genieutils-py, AoE2ScenarioParser, BepInEx, Harmony, UE4SS, REFramework, SKSE, Fabric, 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. Fonts: Space Grotesk and JetBrains Mono (SIL OFL).