Universal Modder for Claude: Set Up and Make Your First Mod

Universal Modder is a free, open-source plugin that lets Claude Code build mods for PC games you own. You add it inside Claude Code with two /plugin commands, describe the mod in plain English, and Claude works out the game's engine, writes the mod, can generate art or sound through the fal API, tests it in the running game and records a short clip. It went viral at the start of October 2026. This guide walks through a first session with Claude; for background on the repository itself see our GitHub Universal Modder overview.

What you need before you start

• Claude Code – Anthropic's coding agent, signed in with a plan or API key that covers your usage.
• The game, installed locally, single-player or mod-friendly. Online games with anti-cheat are excluded by the project.
• Python 3.10+ with uv, ffmpeg for the showcase video, and optionally Blender for 3D models. Git for Windows is recommended on Windows.
• A fal API key only if you want generated sprites, textures, 3D models or sounds – fal bills per request.
• Windows 10 (1809+), macOS 13+ or Ubuntu 20.04+ and at least 4 GB RAM, per the project's requirements.

Step 1: install the plugin in Claude Code

Open a Claude Code session and run:

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

The first command adds the original rehan-remade/universal-modder GitHub repository as a plugin source; the second installs it. Use that exact repository – forks with the same name exist. Restart the session if the new skills don't show up.

Step 2: back up, then point Claude at the game

Copy the game folder and your save files somewhere safe – mods change game files. Then start Claude Code in a working folder and tell it which game you want to mod and where it is installed. The plugin's main skill ("mod any game") starts with reconnaissance: Claude inspects the files, identifies the engine (Unity, Unreal, Godot and other families are covered) and picks the matching mod loader or approach.

Step 3: write a clear mod request

Claude does better with a small, testable goal than with a vague wish. Good first requests look like:

• "Add a new sword with its own sprite to Terraria that's slightly stronger than the iron sword."
• "Make worker units in this game move 20% faster."
• "Add a new tree texture to this Godot game's first level."

Say what should change, how you'll know it works, and whether you want generated assets or placeholders. Start without generated assets if you want to keep the first run cheap.

Step 4: let it build, test and record

Claude then reads the relevant game code, writes the mod, generates assets if asked, launches the game to test, fixes what breaks, and can cut a short showcase video with ffmpeg. Keep Claude Code's permission prompts on so you approve each command it runs, and read the diff of what it changed, as you would with any AI-written code. If you want to share the result, ask it to package the mod with install notes for a site such as Nexus Mods, Steam Workshop, Thunderstore, mod.io or GitHub – and respect each game's modding rules.

Keeping costs under control

The plugin is free (MIT license). What you pay for is the agent's usage and any fal generations. Long recon on big games uses more agent time, and every generated sprite, model or sound is a fal request. Set a spending limit on your fal account, start with one small mod, and reuse assets instead of regenerating them.

Common problems and fixes

• Skills don't appear after install: restart Claude Code and run the install command again; check you added the original repository.
• The game won't launch with the mod: ask Claude to remove the mod and restore the backup, then retry with a smaller change. Mod loaders often need a specific game version.
• Asset generation fails: check that your fal key is set and has credit.
• Online or anti-cheat game: the project won't help, and modding such games can get your account banned.

FAQ

Does Universal Modder only work with Claude?

It's built as a Claude Code plugin. The repository also includes an AGENTS.md file that other agents can read, but the /plugin install is specific to Claude Code.

Is Universal Modder made by Anthropic?

No. It is an independent open-source project by the GitHub account rehan-remade. Anthropic makes Claude Code, the agent it runs in.

Do I need to know how to code?

No, you describe the mod in plain language. Basic familiarity with game folders and mod loaders helps you review changes and recover from mistakes.

Is it safe to use?

The code is open source, so you can read what it does. Install from the original repository, back up your game, keep permission prompts on and set a fal spending limit.

Which games can Claude mod with it?

Most PC games you own across roughly a dozen engine families; the author's demos used Terraria and Age of Empires. Online games protected by anti-cheat are excluded.

Independent guide – not affiliated with Anthropic, fal, the Universal Modder project or any game developer.