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 at universalmodder.com. Publish your mods, remix other people's, and make new ones.
Share what you make, get help, and follow along:
Install
Pick your agent. Each gets the same skills (Agent Skills format), the fal MCP server, and the um CLI.
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)
OpenCode
Clone and run opencode inside it (opencode.json adds the skills and the fal MCP server) or, on OpenCode 2, opencode plugin add 'github:rehan-remade/universal-modder#main::path:plugins/opencode' (the um tool and fal MCP; add the skills with Skills only)
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, 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/).
Without a clone, OpenCode 2 installs the plugin in plugins/opencode/ with opencode plugin add: one
um_run tool that passes its arguments straight to the CLI and runs um from PATH (see below), plus the
fal MCP server when FAL_KEY is set and none is configured. A clone doesn't need it. See
plugins/opencode/README.md.
The um CLI. The Claude Code plugin puts it on PATH (its SessionStart hook), and so does a clone opened in
Claude Code (.claude/settings.json); in a clone with another agent, export PATH="$PWD/bin:$PATH". Other
agents' plugin installs (Codex, Cursor, Gemini CLI, OpenCode) don't, so install it once:
For assets, get a fal API key. It powers both the fal MCP server and
um fal. Rather than exporting it from a shell profile or a .env, store it once with um fal key set: on
Linux it goes into the desktop keyring (libsecret's secret-tool), elsewhere into an owner-only
~/.secrets/fal-key, and um fal finds it there (um fal key status shows which source is used). FAL_KEY
in the environment still works and wins. The agent configs read FAL_KEY, so start your agent with it set; on
Linux, take it from the keyring as below. With no key, fal's OAuth endpoint https://mcp.fal.ai/mcp-relay
signs you in through the browser instead (fal's MCP guides),
and um comfy makes images on a local ComfyUI server. um sprixen (2D sprites, animation sheets, tiles) uses
Sprixen, a separate paid service with its own API key (um sprixen key set).
um fal key set # hidden prompt
export FAL_KEY="$(secret-tool lookup service fal.ai key api)" # Linux: before starting the agent
You also need Git, 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:
search the knowledge base;
recon, then 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;
package;
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.
Open-web research that survives dead forums: Wayback/archive.today, GitHub/code and Nexus/Workshop/Thunderstore APIs, Reddit/YouTube, login-gated handoff, screenshots as evidence
ILSpy / Cpp2IL / Vineflower / Ghidra and IDA over MCP / Cheat Engine / Frida / RenderDoc; reverse-engineer a file format and prove it with a round trip
Port an existing mod to a newer version or loader without drift: one pinned source, a private decompile, data extracted by script, unit-by-unit tests, audits by layer, resumable status docs, and a Forge 1.7.10 → Fabric 1.20.1 mapping table
Search the knowledge base, write your own note, open the PR
Agents (agents/, subagent files with name + description frontmatter): a three-agent team for mods
that take days. Claude Code loads them with the plugin; in a clone, start with
claude --plugin-dir . --agent mod-orchestrator. Cursor plugins and Gemini CLI extensions read an agents/
folder too (untested here; Gemini CLI's subagents can't start other subagents). Three agents use several
times the tokens of one, so keep it for long mods. What worked for one user: the orchestrator on Fable 5.1 at
medium effort, the game worker on Sonnet 5.5 at medium, and the offline worker on Opus 5.5 at high. Any agent can
read the files as role briefs.
The supervisor. Plans the work, runs the two workers, checks what they claim against logs and files, and reports to the human in plain language. Start it as the main session: claude --agent mod-orchestrator
Never touches the game: studies SDK data, dumps and other mods, designs features, writes generators and patches, tests them against stubs, and hands over the exact live probes to run
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 sprixen
sprite (one style per project), animate (sprite id → one-row sheet), tile, projects, credits, key. 2D art from Sprixen's paid API, with a manifest of every generation
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.
Show it off in the Discord, and put the badge on your mod's page:
[](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.
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
universal-modder (rehan-remade/universal-modder)
Choose a tag and it will appear here. With no tags selected, all catalog projects are shown.
Searching Database…
Choose a tag and it will appear here. With no tags selected, all catalog projects are shown.
What is this?Universal Modder gives Claude Code (and other AI coding agents) a set of Agent Skills, a CLI called 'um', and a fal MCP server so the agent can find, reverse-engineer, and mod almost any PC game you own, then generate art, 3D, audio, test the mod in-game, and record a showcase video.
Is this a standalone app, or does it plug into my coding agent?It is not a standalone app. It is a plugin/skill pack: the same Agent Skills, the fal MCP server, and the 'um' CLI get installed into whichever agent you already use (Claude Code, Codex, Gemini CLI, Copilot, Cursor, OpenCode).
How do I install this for Claude Code?Inside Claude Code run '/plugin marketplace add rehan-remade/universal-modder' then '/plugin install universal-modder@universal-modder'. Other agents (Codex, Gemini CLI, Cursor, OpenCode, Copilot) have their own one-line install shown in the README, or you can just git clone the repo and start your agent inside it.
What do I need installed besides the coding agent?You need Git, Python 3.10+, and ffmpeg (uv recommended), plus Blender if you want 3D model to game-sprite rendering. A fal API key powers the fal MCP server and 'um fal' for AI-generated art/audio/3D; without a key you can use 'um comfy' against a local ComfyUI server instead.
Will it mod online multiplayer games or write cheats?No. It only touches games you own and refuses to inject into online games protected by anti-cheat, write cheats against other players, or bypass anti-cheat, DRM, or ownership checks. It also never ships game files or decompiled code in the resulting mod.
Do I need a Windows PC to mod my games?Windows games are driven natively or from WSL, and the window-capture/input automation ('um win') ships as two no-build PowerShell/C# tools, so the heaviest automation features target Windows. The skills and CLI themselves are plain Python and work alongside whichever OS your coding agent runs on.
What is the knowledge/ folder for?It is a shared knowledge base of field notes written by agents for other agents: the exact versions, the route taken, engine quirks, verification steps, and gotchas for games that have already been modded. Agents search it first and can open a PR with their own note when they finish.
What games have already been modded with this?Example projects include a tModLoader weapons pack for Terraria, a new playable civilization for Age of Empires II DE with 3D-rendered units, and real Minecraft running inside GTA V story mode via a Fabric mod plus ScriptHookV/ReShade bridge.
What does the agent actually do when I ask it to mod a game?It follows a fixed 10-step loop: search the knowledge base, recon and pick a route, set up a safe lab with saves backed up, read the real game code, build a working slice, generate assets, verify in the real game, record a video, package the mod, and write a field note for the next agent.
Which coding agents besides Claude Code can use this?Codex, Gemini CLI, VS Code/Copilot Chat, Cursor, and OpenCode are all directly supported with their own install steps; any other agent can just use the skills via 'npx skills add' or a plain git clone.
Universal Modder gives Claude Code (and other AI coding agents) a set of Agent Skills, a CLI called 'um', and a fal MCP server so the agent can find, reverse-engineer, and mod almost any PC game you own, then generate art, 3D, audio, test the mod in-game, and record a showcase video.