universal-modderNEW

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.

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)

Skill

What it does

mod-any-game

The whole loop, hard safety rules, and 12 engine playbooks: Unity, Unreal, .NET/XNA (Terraria, Stardew, Celeste), Godot, Source 1/2, Bethesda, Minecraft, AoE2/Genie, RE Engine/FromSoft/GTA/Cyberpunk/BG3, native C++, indie engines (GameMaker, RPG Maker, Ren'Py, Paradox, Doom, HTML5, LÖVE, Java), retro decomps

game-recon

Prior field notes, engine and version, managed or native, anti-cheat, loaders, save folders, community route → MODDING_PLAN.md

reverse-engineering

ILSpy / Cpp2IL / Vineflower / Ghidra and IDA over MCP / Cheat Engine / Frida / RenderDoc; reverse-engineer a file format and prove it with a round trip

fal-assets

Sprites with real transparency, consistent variants, pixel art, seamless textures, PBR maps, image-to-3D, auto-rigging, SFX, music, voice, cutscene video

asset-pipeline

Art → engine-exact frames: cutout, nearest-neighbour fit, palettes, sheets, team-colour masks, 3D → 8/16-heading sprites

game-automation

Launch, screenshot (GPU-safe), click/type safely, windowed mode, crash-reporter cleanup, in-game agent bridges

showcase-video

Record the window with only the game's audio, pick moments, cut a styled video from an EDL

mashup-mods

Game inside a game: content ports, passthrough mods (worked example: Minecraft × GTA V), decomps as libraries, reimplementations

publish-mod

Lint, package per platform, credits, the post

share-field-notes

Search the knowledge base, write your own note, open the PR

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

Command

What it does

um scan

Find Steam/Epic/Xbox installs; fingerprint engine and version, .NET vs native, anti-cheat, installed loaders, save folders, ranked routes

um fal

sprite, image, edit, rmbg, pixelate, upscale, texture, pbr, model3d, rig, sfx, music, voice, video, run, search, schema, price. Plain REST, with a manifest of every generation

um comfy

status, image (--sprite cuts it out), run (any workflow saved with Export (API)). Images from a local ComfyUI server, no API key

um sprite

cutout, fit, pixelate, palette, sheet, slice, frames, team-mask, seamless, preview

um render3d

GLB → sprite frames from the game's camera (aoe2, iso8, trueiso, topdown, side, turntable) with Blender

um win

shot, record (gfxcapture + process-loopback audio), drive (input that only reaches the game), ps, kill, launch, reg

um video

contact sheets, compile (EDL → titled, beat-cut video with music), mux, beats, first-frame

um backup

Snapshot, diff and restore save folders

um publish check

Blocks shipping game files, decompiled code and leaked keys

um kb

The knowledge base: search, show, new, check, index, sync, pr

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