Universal Modder Claude Code: from install to first mod
Claude Code is the agent the upstream project was built around: one marketplace install brings the skills, the fal MCP server and the um CLI.
Claude Code gets the full toolkit from a single plugin marketplace install. The skills teach the agent the modding loop, the fal MCP server gives it image, audio and 3D generation, and the um CLI gives it deterministic tools for recon, sprite work, backups, recording and packaging. Nothing else needs to be wired up by hand.
This page walks through the whole install on a PC or WSL machine: what to have ready, the exact commands, how to verify the setup without touching a game, and the problems people actually run into. It is written for the copy-paste case, but every command is explained so you can adapt it.
Before you start
- Git, Python 3.10+ and ffmpeg available on PATH.
- uv is recommended for the um CLI; pipx works too.
- A fal API key if you want generated art, audio or 3D (optional — um comfy can use a local ComfyUI server instead).
- Blender only if you plan to render 3D models down to sprites with um render3d.
- A single-player game you own, or a server you host — the toolkit refuses to inject into online games with anti-cheat.
Install steps
- Add the plugin marketplace. In a Claude Code session, run /plugin marketplace add rehan-remade/universal-modder. This registers the upstream repository as a plugin source you can install from.
- Install the universal-modder plugin. Run /plugin install universal-modder@universal-modder. One install brings the Agent Skills set, the fal MCP server configuration and the um CLI onto your machine.
- Set your fal key for asset generation. Export FAL_KEY in your shell profile (use setx FAL_KEY on Windows) so um fal and the fal MCP can generate sprites, textures, audio and 3D without a local ComfyUI server. Skip this and asset steps fall back to um comfy or plain error out.
- Confirm the um CLI is on PATH. Open a new terminal and run um --help. If the command is missing, install it directly with uv tool install git+https://github.com/rehan-remade/universal-modder and restart the shell.
- Point the agent at a game you own. Start Claude Code in or near the game folder and describe the mod in plain language, for example: mod Terraria — add a homing missile launcher and a tactical nuke, sprites from fal. The mod-any-game skill takes over from there.
- Follow the loop and review its checkpoints. The agent searches the knowledge base, runs recon, builds a safe lab with save backups, reads the game's code, ships one working slice, generates assets, verifies in the running game, records the result, packages the mod, and writes a field note for the next agent.
Verify the installation
Two commands prove the install works before you touch a game: um --help prints the CLI surface, and um kb search queries the community knowledge base without needing a repository clone.
um --help
um kb search "terraria"Common problems and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| um: command not found right after installing the plugin. | The CLI is put on PATH by the plugin install, but terminals that were already open keep the old PATH. | Open a new terminal. If it is still missing, run uv tool install git+https://github.com/rehan-remade/universal-modder and restart the shell. |
| Asset generation fails with FAL_KEY is not set. | um fal and the fal MCP server both need a fal API key, and neither ships with one. | Create a key at fal.ai/dashboard/keys, export FAL_KEY in your shell profile, then restart Claude Code so the MCP server picks up the new environment. |
| The skills never trigger when you ask for a mod. | Claude Code loads skills when a session starts, so a session that began before the plugin install will not see them. | Restart the session, then ask again with the game name and the mod you want. Cloning the repository and starting the agent inside it also works. |
| um render3d fails while 2D sprite commands work fine. | Rendering 3D models to sprite frames shells out to Blender, which is a separate install. | Install Blender and make sure it is on PATH. Sprite work through um sprite and um fal does not need Blender. |
Why install through the plugin instead of cloning
The marketplace route installs the same skills, MCP server and CLI as a clone, and keeps um on PATH for you. Cloning is still the fallback for any agent without a plugin system: the repository's AGENTS.md, skills and .mcp.json are read from the working directory, so an agent started inside the clone behaves the same way.
What the agent asks before it touches your game
Universal Modder backs up saves before edits, kills processes by PID only, and asks before driving your mouse and keyboard, installing loaders into game folders, or publishing anything. It refuses to inject into online games with anti-cheat, write cheats against other players, or ship game files and decompiled code. Full reasoning lives upstream in skills/mod-any-game/references/safety.md.