Independent guides for the Universal Modder toolkit

Universal Modding is a third-party documentation site foruniversal-modder, the open-source toolkit that lets AI coding agents mod PC games you already own. It is not a mod manager, not an emulator and not a cheat tool: it is a toolkit that gives a coding agent a repeatable loop — search prior field notes, fingerprint the engine, back up saves, read the real code, build one working slice, generate assets, verify in-game, record, package, and write up what it learned.

Quick start

Both agents install the same package: the twelve Agent Skills, the fal MCP server and the um CLI. A fal key is optional for the first run — without it you can still do recon, coding, testing and packaging.

/plugin marketplace add rehan-remade/universal-modder
/plugin install universal-modder@universal-modder
export FAL_KEY=...  # optional, for generated assets

codex plugin marketplace add rehan-remade/universal-modder
codex plugin add universal-modder@universal-modder
export FAL_KEY=...  # optional, for generated assets

Using Gemini CLI, Copilot, Cursor or OpenCode? The install guide has the exact command for every agent, plus prerequisites and verification steps.

What Universal Modder is — and is not

The toolkit lives upstream as an MIT-licensed repository of skills, tools and a shared knowledge base. You point an agent at a game, describe the mod, and the agent follows the same loop every time. Three things it is commonly mistaken for:

• It is not a mod manager — there is no mod list UI, no load order screen and no Vortex-style library. When a game uses a loader like tModLoader or Fabric, the agent builds against that loader.
• It is not an emulator — it drives the copy of the game you already have installed, natively on Windows or from WSL.
• It is not a cheat tool — it refuses to inject into online games with anti-cheat, to write cheats against other players, or to bypass DRM and ownership checks.

The ten-step agent loop

Every session, whatever the engine, follows the same sequence. The order is the point: it keeps the agent from rewriting a game before it understands it, and from touching saves before they are backed up.

1. Search the shared knowledge base for prior field notes on the game or engine.
2. Run recon: fingerprint engine and version, check anti-cheat, loaders and save folders.
3. Set up a safe lab: back up save folders and pick a disposable test profile.
4. Read the actual code — decompile or disassemble only as far as needed.
5. Build one working slice before adding scope.
6. Generate art, audio or 3D assets with fal, then convert them to engine-exact formats.
7. Verify in the running game, with automated screenshots and safe input.
8. Record the result so the mod can be shown, not just claimed.
9. Package the mod for its platform with credits and a publish check.
10. Write a field note so the next agent starts where this one finished.

What the toolkit can do

Supported coding agents

• Claude Code — the agent the upstream project was built around.
• Codex — plugin marketplace install, same package.
• Gemini CLI — installed as an extension.
• VS Code / Copilot — installed as a chat plugin.
• Cursor — marketplace or clone.
• OpenCode — clone and run inside the repository.

Engine playbooks

The mod-any-game skill carries structured playbooks for the engine families with known routes. If a game runs on one of these, the agent starts with a plan instead of a blank page:

• Unity
• Unreal Engine
• .NET / XNA (Terraria, Stardew Valley, Celeste)
• Godot
• Source 1 / Source 2
• Bethesda (Creation Engine)
• Minecraft (Java / Bedrock)
• Age of Empires II / Genie
• Mount & Blade Bannerlord
• AAA native engines (RE Engine, MT Framework, FromSoft, GTA, Hedgehog, Black Rock, Cyberpunk, BG3)
• Native C++
• Indie engines (GameMaker, RPG Maker, Ren'Py, Paradox, Doom, HTML5, LÖVE, Java)
• Retro decompilations

Worked examples from the community

The upstream repository ships full case studies, and the knowledge base carries field notes from other agent sessions. Notable ones: Fal Arsenal for Terraria on tModLoader (homing missiles, a tactical nuke that craters the world, a chain-lightning rifle, new enemies and a two-phase boss), a new civilization for Age of Empires II DE with a Robotaxi unique unit rendered at the game's camera angle, and real Minecraft running inside GTA V story mode over a local WebSocket bridge.

Safety boundaries

• Any game you own: single-player, plus multiplayer and servers you host yourself.
• No injection into online games with anti-cheat, and no cheats against other players.
• No anti-cheat, DRM or ownership bypasses, ever.
• Saves are backed up before edits; processes are killed by PID only.
• The agent asks before driving your input, installing loaders into game folders, or publishing.
• Mods ship as code, your own assets and converters — never game files or decompiled code.

Frequently asked questions

Everything on this site is independent work, written by people who use the toolkit. The upstream repository is linked in the footer so you can always check the source yourself.