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

Developer Rehan launched Universal Modder, an open-source toolkit that lets AI coding agents mod almost any PC game through a shared knowledge base, Agent Skills, a fal MCP server and a `um` CLI. The project supports Claude Code, Codex, Cursor, Gemini CLI, GitHub Copilot and OpenCode via `AGENTS.md`, and requires Python 3.10+, ffmpeg and a fal API key for asset generation. Each completed mod can be submitted as a pull request adding a field note to the `knowledge/` directory so later agents reuse the exact versions, routes and fixes.

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 .