# Universal Modder: Let Any AI Coding Agent Mod Almost Any PC Game

> Source: <https://github.com/rehan-remade/universal-modder>
> Published: 2026-10-01 02:48:15+00:00

**Skills, tools and a shared knowledge base that let any AI coding agent mod almost any PC game you own.**

  Works with Claude Code, Codex, Cursor, Gemini CLI, GitHub Copilot, OpenCode, or anything that reads `AGENTS.md`.

  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](https://fal.ai), tests it in the running game, cuts the video, and writes down what it learned for the next agent.

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` , then`/plugin install universal-modder@universal-modder` | 
| **Codex** | `codex plugin marketplace add rehan-remade/universal-modder` , then`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` ) | 
| **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 and friends),
`.claude/skills`, `.gemini/skills` and `.github/skills` all link to `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` and `.vscode/mcp.json`.

**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](https://fal.ai/dashboard/keys). It powers both the fal MCP server and
`um fal`:

```
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.

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.

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.

[`knowledge/`](https://github.com/rehan-remade/universal-modder/blob/main/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`](https://github.com/rehan-remade/universal-modder/blob/main/knowledge/INDEX.md). Contribution rules, for humans and AIs, are in
[`CONTRIBUTING.md`](https://github.com/rehan-remade/universal-modder/blob/main/CONTRIBUTING.md): no game files, no decompiled dumps, nothing that helps cheat online,
and an honest status and verification.

**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.

| `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 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#.

- **[examples/terraria-tmodloader](https://github.com/rehan-remade/universal-modder/blob/main/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](https://github.com/rehan-remade/universal-modder/blob/main/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](https://github.com/rehan-remade/universal-modder/blob/main/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](https://github.com/rehan-remade/universal-modder/blob/main/knowledge/INDEX.md).

- **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,
PRs included.

Full reasoning: [`skills/mod-any-game/references/safety.md`](https://github.com/rehan-remade/universal-modder/blob/main/skills/mod-any-game/references/safety.md).

- Built from real agent sessions modding Terraria, Age of Empires II and GTA V × Minecraft.
- Assets: [fal](https://fal.ai) (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. Fonts: Space Grotesk and JetBrains Mono (SIL OFL).