GitHub Universal Modder: Claude Code Game Mod Plugin Guide

Universal Modder (universal-modder on GitHub, by the account rehan-remade) is a free, MIT-licensed plugin that teaches an AI coding agent – mainly Claude Code – to build mods for PC games you own. It bundles agent skills, a command-line helper called um, and an MCP connection to the fal media API, so the agent can identify a game's engine, read its code, write the mod, generate sprites, 3D models or audio, test the mod in the running game and record a short showcase video. You install it from inside Claude Code with two /plugin commands.

The project went viral at the start of October 2026 after its author posted demos of Claude modding Terraria and Age of Empires. Below is what it is, how to set it up, and what to watch out for.

What is Universal Modder?

Universal Modder is not a mod loader and not a standalone app. It is a set of instructions and tools for an AI agent. Mod loaders like BepInEx (Unity), tModLoader (Terraria) or engine-specific tools still do the low-level work; the plugin tells the agent which loader fits which engine, how to inspect the game, and how to check that a change actually works.

According to the project and coverage of it, the package contains:

• Engine playbooks – instructions for about a dozen engine families (Unity, Unreal and Godot are among those mentioned), so the agent can recognise the engine and pick a matching mod loader.
• The um CLI – a command-line helper the agent uses to interact with the game while it builds and tests a mod.
• fal MCP integration – lets the agent generate sprites, textures, 3D models and sound effects for the mod through fal (a paid media-generation API; you need your own key).
• A main skill, mod-any-game – runs a project from idea to finished mod: recon, code, assets, in-game testing and packaging.

The repository also ships an AGENTS.md, so other agents that read that file (for example OpenAI Codex or Cursor) can use the same instructions, although Claude Code is the primary target.

How to install Universal Modder from GitHub

The simplest route is Claude Code's plugin marketplace. In a Claude Code session, run:

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

The first command registers the GitHub repository as a plugin source; the second installs the plugin from it. Alternatively you can clone the repository and start Claude Code inside the folder so it picks up the project's CLAUDE.md and skills directly.

Make sure you install from the original rehan-remade/universal-modder repository. Forks with the same name already exist; a fork is not automatically malicious, but the original is where fixes and releases land.

Requirements

The published requirements are modest, but the toolchain has a few parts:

Need	Details
Operating system	Windows 10 (1809 or later), macOS 13+ or Ubuntu 20.04+
Memory	4 GB RAM minimum
Python	3.10 or later, plus the uv package manager
Video	ffmpeg (for recording the showcase clip)
3D (optional)	Blender, for converting generated 3D models
Windows extra	Git for Windows is recommended
Accounts	Claude Code (or another agent) and a fal API key for generated assets

You also need a legitimate copy of the game you want to mod, installed locally.

How a modding session works

Once installed, you describe the mod you want in plain language – for example "add a new sword with a custom sprite to Terraria" or "make villagers in this Unity game move faster". The agent then works through roughly these steps:

1. Find the game and inspect its files.
2. Identify the engine and choose the matching mod loader or modding approach.
3. Read the real game code (decompiling or inspecting scripts where the engine allows it) to find where to hook in.
4. Write the mod and, if needed, generate assets – sprites, textures, models or audio – through fal.
5. Test in the running game and fix what breaks.
6. Record a short showcase video and, if you want, package the mod for Nexus Mods, Steam Workshop, Thunderstore, mod.io or GitHub with install notes.

You stay in the loop: the agent asks for permission before running commands, and you should read what it changes, as with any AI-written code.

What it won't do: anti-cheat and online games

The project explicitly rules out:

• Modding online games protected by anti-cheat (Easy Anti-Cheat, BattlEye, VAC and similar).
• Building multiplayer cheats or bypassing protection systems.
• Distributing game files or working on games you don't own.

That matters for your own account as well: injecting code into a protected online game can get you banned regardless of what tool wrote the code. Stick to single-player or mod-friendly games.

Is Universal Modder safe?

The code is open source under the MIT license, so you can read exactly what the skills and the um tool do before installing. Practical precautions:

• Install from the original repository and check recent commits and issues.
• Back up your game folder and save files before the first run – mods change game files.
• Keep Claude Code's permission prompts on so you approve each command.
• Set a spending limit on your fal account, because asset generation is billed per request.

FAQ

Is Universal Modder free?

Yes, the plugin itself is free and MIT-licensed. You still pay for the AI agent you run it with (for example a Claude plan or API usage) and for any assets generated through fal.

Which games does Universal Modder support?

It targets "almost any PC game you own" by covering roughly a dozen engine families, including Unity, Unreal and Godot games. The author's demos used Terraria and Age of Empires. Games protected by anti-cheat and online multiplayer games are excluded.

Does it work with Codex or Cursor?

The repository includes an AGENTS.md file, so agents that read it can follow the same instructions. The plugin install commands are specific to Claude Code.

Do I need to know how to code?

No, you describe the mod in plain language. Some familiarity with game folders, mod loaders and reading code helps you review the changes and fix problems the agent can't.

Where do I download Universal Modder?

From GitHub: the original repository is rehan-remade/universal-modder. Inside Claude Code you don't need to download anything manually – the two /plugin commands above fetch it.

Universal Modder is an independent open-source project; it is not made by Anthropic, OpenAI, fal or any game developer.