Universal Modder: Let AI Agents Mod Almost Any PC Game

Game modding usually requires several different specialties at once: identifying the engine, locating the right files, understanding undocumented formats, writing a loader or patch, creating compatible assets, testing safely, and documenting the result. universal-modder packages that workflow for AI coding agents so they can approach unfamiliar PC games systematically rather than guessing their way through a one-off experiment.

The project supports Claude Code, Codex, Cursor, Gemini CLI, GitHub Copilot, OpenCode, and other agents that read AGENTS.md. Its central promise is not that every game is instantly moddable. Instead, it gives an agent a repeatable investigation and delivery process for games you own, with safety boundaries and a shared knowledge base that preserves discoveries between projects.

What the project adds to an AI coding agent

Universal Modder combines three major components:

• Agent Skills for reconnaissance, reverse engineering, asset pipelines, automation, video production, and publishing.
• The um command-line tool for scanning installations, managing saves, generating assets, driving Windows games, and maintaining field notes.
• A fal MCP server for generating sprites, textures, 3D models, sound effects, music, voices, and video.

The agent follows a consistent loop:

1. Search existing knowledge about the game.
2. Recon the installation, engine, version, loaders, save locations, and anti-cheat situation.
3. Choose a viable modding route.
4. Back up saves and establish a safe test environment.
5. Read the actual code or data formats instead of relying on assumptions.
6. Build one small working slice.
7. Generate or adapt the required assets.
8. Verify the mod in the running game.
9. Record a gameplay showcase.
10. Package the result and write a field note for future agents.

That sequence is important. It makes the agent behave more like a junior reverse engineer working under a documented process than like a chatbot producing speculative code.

Installation options

For Claude Code, add the marketplace and install the plugin:

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

Codex uses:

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

Gemini CLI can install the extension directly:

gemini extensions install https://github.com/rehan-remade/universal-modder

For an agent that supports the Agent Skills format:

npx skills add https://github.com/rehan-remade/universal-modder

Alternatively, clone the repository and start an agent inside it:

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

The repository places links to the shared skills/ directory in the locations expected by different agents, including .agents/skills, .claude/skills, .gemini/skills, and .github/skills. Agent instructions are provided through AGENTS.md, with CLAUDE.md and GEMINI.md pointing to the same guidance. MCP configuration is available for .mcp.json, Codex, Cursor, and VS Code.

The CLI can also be installed independently:

uv tool install git+https://github.com/rehan-remade/universal-modder
# or
pipx install git+https://github.com/rehan-remade/universal-modder

You need Python 3.10 or newer and ffmpeg. The project recommends uv, and Blender is required when converting 3D models into sprite renders. Windows games can be controlled natively or from WSL.

Using fal for generated game assets

Universal Modder uses fal both through MCP and through um fal. Set an API key before generating assets:

export FAL_KEY=your_key_here

The fal wrapper exposes commands for image and game-asset production, including:

• sprite, image, edit, rmbg, pixelate, and upscale
• Texture and PBR-map generation
• Image-to-3D model creation
• Rigging
• Sound effects, music, voice, and video
• Model search, schema inspection, pricing, and execution

Generated assets are tracked with a manifest, which is useful for reproducibility and attribution. The separate asset pipeline then converts generic generated output into engine-specific content: transparent cutouts, nearest-neighbor pixel art, palettes, sprite sheets, team-color masks, seamless textures, and camera-matched 3D renders.

For example, the 3D workflow can render a GLB model into eight or sixteen directional frames for an Age of Empires II-style camera. The 2D workflow can transform generated art into a correctly sized Terraria sprite, such as a 64x26 in-game asset.

Skills cover the entire modding lifecycle

The mod-any-game skill includes playbooks for twelve broad engine and technology families, including Unity, Unreal, .NET/XNA games such as Terraria and Stardew Valley, Godot, Source 1 and 2, Bethesda games, Minecraft, AoE2/Genie, RE Engine, FromSoftware titles, GTA, Cyberpunk, Baldur’s Gate 3, native C++, and several indie and retro ecosystems.

Other skills handle specialized work:

• game-recon identifies engines, versions, loaders, save folders, and community-supported routes.
• reverse-engineering covers tools such as ILSpy, Cpp2IL, Vineflower, Ghidra, IDA, Cheat Engine, Frida, and RenderDoc.
• game-automation launches games, captures screenshots, drives input, handles windowed mode, and cleans up crash reporters.
• showcase-video records game-only audio, builds contact sheets, and compiles edited videos from an EDL.
• mashup-mods supports cross-game experiments and passthrough architectures.
• publish-mod checks packages for prohibited files and prepares credits and release material.

A knowledge base designed for agents

The knowledge/ directory is one of the repository’s most useful ideas. It stores field notes describing how specific games were actually modified, including:

• The exact versions that worked
• The selected route and why it was chosen
• What the engine really does
• How the result was verified
• Gotchas expressed as symptom, cause, and fix

Agents can search this material before starting a new project:

um kb search "grand theft auto"

A new note can be created and validated with:

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

After human approval, the note can be submitted as a pull request:

um kb pr knowledge/games/hades-ii/a-new-boon-god.md --yes

The contribution rules explicitly prohibit game files, decompiled dumps, material that enables online cheating, and dishonest verification claims. The goal is to preserve practical knowledge without turning the repository into a distribution channel for copyrighted game data or multiplayer cheats.

Included examples

The repository includes three substantial examples.

Terraria tModLoader

The Terraria example, called Fal Arsenal, adds a homing missile launcher, tactical nuke, chain-lightning rifle, black-hole gun, orbital strike, three enemies, and a two-phase Drone Mothership boss. All of the sprites were generated with fal and then adapted to the game’s asset requirements.

Age of Empires II: Definitive Edition

The San Franciscans example adds a civilization with a Robotaxi unique unit, Delivery Drones, and a Transamerica Pyramid wonder. Units were created from fal image-to-3D models and rendered from the game’s camera angle. The project also includes a reverse-engineered .sld sprite writer.

Minecraft inside GTA V

The most ambitious example places real Minecraft inside GTA V story mode. A Fabric mod and a ScriptHookV plus ReShade add-on communicate over a local WebSocket. Minecraft color and depth are composited into the GTA frame, while Minecraft TNT, arrows, and fireworks become GTA explosions and bullets. Minecraft mobs can even fight the police.

These examples demonstrate that the repository is intended for more than ordinary configuration tweaks. It supports source-level mods, asset conversions, runtime bridges, and carefully scoped game mashups.

Safety boundaries are part of the design

Universal Modder is explicitly aimed at single-player and offline modding for games the user owns. Its instructions refuse to inject into online games with anti-cheat, create multiplayer cheats, or bypass anti-cheat, DRM, or ownership checks.

The workflow also includes operational safeguards:

• Back up save folders before modifying them.
• Kill processes by PID rather than using broad process termination.
• Ask before controlling the mouse and keyboard.
• Ask before installing loaders into game directories.
• Ask before publishing or opening pull requests.
• Use um publish check to block game files, decompiled code, and leaked keys from release packages.

The repository is MIT licensed and currently consists primarily of Python, with the language breakdown listed as 89.4% Python, 10% PowerShell, and 0.6% Shell. Two no-build Windows utilities ship inside um/ps1/: WinDrive for controlled input and ProcLoopback for capturing game-only audio, both implemented as PowerShell scripts with embedded C#.

Why this project matters

The interesting shift is from “ask an AI to make a mod” to “give an AI an engineering system for modding.” Reconnaissance, version tracking, backups, repeatable asset conversion, in-game verification, and shared field notes address the parts of modding that are usually invisible in a short demo.

The result will still depend on the game, its version, its community tooling, and the agent’s ability to inspect unfamiliar code. However, universal-modder makes those dependencies explicit. For developers interested in AI-assisted tooling, reverse engineering, or procedural game content, it is a practical example of how skills, MCP tools, CLI utilities, and accumulated project knowledge can work together as one agent-facing workflow.

Repository: rehan-remade/universal-modder

Source

rehan-remade/universal-modder: Point Claude at any game. Skills, tools and the fal MCP that let Claude Code mod almost any PC game you own: recon, reverse engineering, fal-generated art/3D/audio, in-game testing, showcase videos.