Universal Modder for Claude Code: Install, fal Costs, Limits

Universal Modder, the open-source repo rehan-remade/universal-modder, is not an app that mods games by itself. It is a free, MIT-licensed kit that gives an AI coding agent such as Claude Code or Codex a method for modding PC games you own: Agent Skills with engine playbooks, a Python command-line tool called um, a preconfigured connection to fal for generating sprites, 3D models and sound, and a library of field notes from earlier mods. The agent still does the work. You need a paid agent plan, a game with a workable modding route, and usually a fal API key, which bills per generation. Online games with anti-cheat are off-limits under the toolkit's own rules, and its automated in-game testing runs only on Windows or WSL.

What was tested, and what wasn't. On October 6, 2026, the plugin was installed into Claude Code 2.1.288 on a Mac, and a set of um commands was run against dummy files (repo commit 76b9c7e, um 0.2.0). No game was scanned, modded or launched. No mod was built, no fal asset was generated, and no money was spent. The Codex, Gemini CLI, Cursor, Windows and WSL routes were not tried. Every code block below is labeled either Ran (trimmed real output from that session) or README (copied from the project's instructions, not run).

What Universal Modder is: an agent toolkit, not a mod generator

The repo was created on September 30, 2026, and had 4,225 GitHub stars as of October 6, 2026, with new commits landing daily. Its package version is 0.2.0. The repo describes itself as "Skills, tools and the fal MCP that let Claude Code mod almost any PC game you own," and the README adds install routes for Codex, Cursor, Gemini CLI, GitHub Copilot and OpenCode.

Installing it gives your agent four things:

• Ten Agent Skills. The entry point, mod-any-game, holds the overall workflow, the safety rules and 12 engine playbooks, covering Unity, Unreal, .NET/XNA games such as Terraria and Stardew Valley, Godot, Source, Bethesda, Minecraft, Age of Empires II, native C++ and a long tail of indie engines. The other skills cover recon, reverse engineering, fal assets, sprite pipelines, game automation, showcase videos, "game inside a game" mashups, publishing and field notes.
• The um CLI. scan finds installed games and fingerprints the engine, anti-cheat, loaders and save folders. fal and comfy generate assets, sprite and render3d turn art into game-ready frames (render3d needs Blender), win controls Windows games, backup snapshots saves, publish check screens a mod before release, and kb searches the field notes.
• The fal MCP server. fal's hosted server at https://mcp.fal.ai/mcp, authenticated with your FAL_KEY, lets the agent search models, check prices and run generations.
• Field notes. The knowledge/ folder holds notes that agents wrote after finishing a mod: the versions that worked, the route and why, how the result was verified, and the gotchas.

The mod-any-game skill makes the agent follow the same ten steps each time: search the field notes, recon the game and pick a route, set up a lab with saves backed up, read the game's actual code, get one small slice working, generate assets, verify in the running game, record, package, and write a field note. The kit supplies method and tools. Whether a particular game ends up with a working mod still depends on its engine, the loaders available for it, and the agent session.

Two names get mixed up with it. Videos titled "Claude Mods" cover a separate Claude Code feature that has nothing to do with this repo, and drago-suzuki58/universal_modloader on GitHub is a different project.

Tested on October 6, 2026: plugin install and offline um commands, no game

Everything in this table ran on macOS 26 with Python 3.12 against commit 76b9c7e. The save files, images and mod folder were dummies made for the test.

Not run: anything inside a real game (scanning an installed game, installing a loader, building a mod, checking it in game), any fal or ComfyUI generation, Blender renders, um video, Windows or WSL, the installs for Codex, Gemini CLI, Copilot, Cursor and OpenCode, and a chat session in which Claude actually used the skills. The mods described in the next section are the author's examples and were not reproduced.

Can Claude Code mod games with Universal Modder? The author's examples say yes

The repo ships three worked examples, each with a field note. These are the author's claims:

• Fal Arsenal for Terraria, built on tModLoader: a homing missile launcher, a tactical nuke that craters the world, a chain-lightning rifle, a black-hole gun, an orbital strike, three new enemies and a two-phase Drone Mothership boss. The README says every sprite came from fal, and the field note mentions a video with about 400,000 views.
• San Franciscans for Age of Empires II DE: a new civilization with a Robotaxi unique unit, Delivery Drones rendered from fal image-to-3D models, a Transamerica Pyramid wonder and a reverse-engineered writer for the game's .sld sprite format.
• Minecraft inside GTA V story mode: a Fabric mod and a ScriptHookV plus ReShade add-on that exchange camera, ground and game events over a local WebSocket, so Minecraft TNT blows up GTA cars.

So can it create new weapons and enemies? The Terraria example is exactly that. The README doesn't say how many attempts, hours or tokens these mods took, so treat them as proof that the approach can work, not as a measure of effort.

The examples also show where to start. Games with an established mod loader and existing field notes, such as Terraria through tModLoader, give the agent a documented route. A native game with no known route sends it into reverse engineering. When um scan ran on the Terraria example folder, it listed both kinds of route:

Ran (um scan on the repo's example folder, trimmed):

$ um scan universal-modder/examples/terraria-tmodloader
  engine:    Unknown native engine  [10%]  evidence: no known engine signature
  anti-cheat: none found
  loaders:   none installed
  routes:
    1. tModLoader (free Steam app 1281930): C# ModItem/ModNPC/ModProjectile/ModSystem, hot reload from ModSources
    2. proxy-DLL loader + function hooks (MinHook/SafetyHook), memory reading; Ghidra/IDA + x64dbg + Cheat Engine

The engine guess is weak because that folder holds the example mod's source code, not the game's files. The route list still recognized Terraria by name and put the free tModLoader app first.

Requirements: a paid agent plan, Python 3.10+, ffmpeg, Windows

• An agent you can run. For Claude Code, Anthropic's Claude Code setup docs say it "requires a Pro, Max, Team, Enterprise, or Console account" and that the free Claude.ai plan doesn't include it. You also have to be in one of Anthropic's supported countries; the US is on the list. Claude Code runs on macOS 13+, Windows 10 1809+, Ubuntu 20.04+ and Debian 10+, with at least 4 GB of RAM. For plan prices, see the Claude Code Pricing Guide 2026; for setup, see How to Install Claude Code.
• Git, Python 3.10+ and ffmpeg, with uv recommended. Without uv, the plugin's um launcher falls back to the system python3, which then needs pip install pillow numpy.
• Blender, only if you want 3D models turned into sprite frames.
• A fal API key for cloud-generated art, 3D and audio. Without one, um comfy can generate images through a local ComfyUI server, with no audio, 3D or video.
• A copy of the game you own. The README says Windows games are driven natively or from WSL, which matters for the testing step (see the Mac section below).

How to install Universal Modder in Claude Code

The README's route is two commands typed inside a Claude Code session:

README (not run in this form):

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

The test used the equivalent claude plugin subcommands from a terminal, with a fresh, empty Claude Code config folder:

Ran (Claude Code 2.1.288 on macOS, trimmed):

$ claude plugin marketplace add rehan-remade/universal-modder
Adding marketplace…Cloning via SSH: git@github.com:rehan-remade/universal-modder.git
✔ Successfully added marketplace: universal-modder (declared in user settings)

$ claude plugin install universal-modder@universal-modder
✔ Successfully installed plugin: universal-modder@universal-modder (scope: user)

$ claude plugin list
  ❯ universal-modder@universal-modder
    Version: 76b9c7e77ead
    Scope: user
    Status: ✔ enabled

None of these commands asked for a login. The marketplace was cloned over SSH on a machine that had GitHub SSH access. A machine without SSH keys was not tried, so if the clone step fails, check your GitHub access first.

The plugin puts um on your PATH, according to the README. Running the copy inside the plugin folder with plain system Python returned universal-modder 0.2.0. For assets, the README's next step is to set your key, which both the fal MCP server and um fal read:

README:

export FAL_KEY=...

Without it, fal commands stop before sending anything:

Ran:

$ um fal price fal-ai/trellis-2
um: FAL_KEY is not set. Create a key at https://fal.ai/dashboard/keys and `export FAL_KEY=...` (or put FAL_KEY=... in a .env file here)

If you use a different agent, the README lists these routes. None of them were run:

For a wider look at what else to add to Codex, see Which Codex Plugins Should You Install First?. If you're unsure how plugins, skills and hooks differ in Claude Code, Claude Code Hooks vs Skills vs Slash Commands explains the split.

Is universalmodder.org the official site? The GitHub repo doesn't link to it

According to whois, universalmodder.org was registered on October 5, 2026, five days after the repo was created. The GitHub repo's homepage field is empty, and no file in the repo mentions the domain. As of October 6, 2026, the site links back to the GitHub repo and collects newsletter sign-ups and contact messages. It offers no separate download.

Nothing shows the site is malicious, and nothing ties it to the repo's author either. Install through your agent's plugin command or from the universal-modder repository on GitHub. The repo's own safety notes warn that a viral mod's "download" is often malware.

First session on a game you own: scan, back up saves, then one small change

The toolkit's workflow front-loads recon and backups. The um side of that can be checked before any agent session starts.

1. Find your games. um scan --list looks for Steam, Epic and Xbox installs. Its code also checks Steam's default folders on macOS and Linux, which was not tested with a game installed. On the test Mac it found nothing:

   Ran (trimmed; the message goes on to suggest passing a game folder to um scan):

   Copy

   $ um scan --list
   no Steam/Epic/Xbox installs found

2. Check for field notes on your game. If a note exists, the agent starts from a route that already worked:

   Ran (trimmed):

   Copy

   $ um kb search terraria
   games/terraria/fal-arsenal-tmodloader.md
      Fal Arsenal: missiles, a tactical nuke, new enemies and a boss for Terraria  [Terraria | xna-fna | loader-api | working]
   games/terraria/eye-of-cthulhu-rl-agent.md
   techniques/driving-real-games-safely.md
   techniques/oracles-how-agents-know-a-mod-works.md
   techniques/recording-game-footage.md

3. Back up the save folder before anything touches it. A restore first snapshots the current state, so the restore can be undone too. New files stay unless you add --clean. This round trip used dummy .wld files, not a real Terraria save:

   Ran (dummy files, paths shortened):

   Copy

   $ um backup create saves --name demo-saves
   ~/.universal-modder/backups/demo-saves/20261006-210035.zip  (1 files, 0.0 MB)
   
   $ um backup diff demo-saves saves
   {
    "snapshot": "~/.universal-modder/backups/demo-saves/20261006-210035.zip",
    "target": "saves",
    "added": [
     "world2.wld"
    ],
    "removed": [],
    "changed": [
     "world1.wld"
    ]
   }
   
   $ um backup restore demo-saves --yes
   restore 20261006-210035.zip -> saves: 1 changed, 0 missing, 1 new since (new files kept)
   ~/.universal-modder/backups/demo-saves-pre-restore/20261006-210112.zip  (2 files, 0.0 MB)
   restored 1 files

4. Ask the agent for recon before a build. The game-recon skill writes a MODDING_PLAN.md with the engine, anti-cheat, loaders, save folders and the community route. A first prompt can be as narrow as "Recon Terraria and write MODDING_PLAN.md, then stop before installing anything." That prompt is a suggestion and was not run. The README's own sample prompts aim higher, for example:

   Mod Terraria: add a homing missile launcher and a tactical nuke that craters the world. Make the sprites with fal.

5. Get one item or one enemy working in the game before generating a batch of art. That matches the skill's "one working slice" step, and it keeps fal spending small until the route is proven.

The rules say the agent asks before it installs loaders into game folders, drives your mouse and keyboard, or publishes anything. Expect those prompts, and read what it plans to put in the game folder.

Universal Modder cost: free code, about $0.21 per default sprite

The code costs nothing. The two bills are your agent plan and fal. The table maps each um fal recipe to its default model and the price on fal's model pages as of October 6, 2026.

Sources: fal model pages for Nano Banana 2, GPT Image 2, Trellis 2 and ElevenLabs sound effects v2. Prices change, and the repo's defaults do too, since "Model ids move fast," as um fal --help puts it.

Example: a small mod with 10 sprites, 1 piece of key art, 1 3D model and 5 two-second sound effects. The 3D model uses the $0.30 middle price.

Those are list prices for one attempt each. Art rarely lands on the first try. If every sprite took three tries at the default quality, the sprites alone would cost 30 × $0.211 = $6.33, and the mod $6.73.

Two practical points follow. First, pixel-art sprites get shrunk to the game's frame size anyway. The test above fitted a 512×512 image into 32×32, so trying --quality medium before paying for high is reasonable. Second, the fal-assets skill tells the agent to check prices before batching 3D, video or long music, and to tell you the rough cost before more than about 20 generations. Video and music are the open-ended items in this budget.

The agent is the other bill, and it doesn't show up in fal's dashboard. Claude Code needs at least a Pro plan, and a session that decompiles a game, writes code and retries builds draws on that plan's usage limits. The Claude Code Pricing Guide 2026 covers which plan fits heavier use.

Does Universal Modder work on Mac or Linux? Setup yes, game control no

On macOS, every um command in the test worked except game control. um win, the part that launches games, takes screenshots, sends input and records game-only audio, refused to run:

Ran (macOS 26):

$ um win ps
um: `um win` drives Windows games (native Windows or WSL). On Linux use xdotool/ydotool + ffmpeg x11grab/pipewire; on macOS use screencapture + ffmpeg avfoundation (see skills/game-automation).

The game-automation skill describes itself as "Windows-first (also from WSL), with notes for Linux and macOS." On a Mac or Linux machine, the agent can plan, write code and generate assets. The "verify in the real game" step falls to you, or to capture tools the agent sets up from those notes.

Will Universal Modder get you banned? Anti-cheat games are a hard stop

The README and the toolkit's safety rules file set these limits for the agent:

• Any game you own, whether single-player, multiplayer or a server you host. It refuses to inject into online games with anti-cheat, write cheats against other players, or bypass anti-cheat, DRM or ownership checks.
• Named anti-cheat systems are a stop sign for code injection: EasyAntiCheat, BattlEye, Vanguard, EA Javelin, Ricochet, ACE, nProtect, XIGNCODE and mhyprot. Official mod tools such as Workshop, map editors and mod kits are allowed, and so are official offline modes that ship without the anti-cheat. The safety file calls launching Elden Ring offline through ModEngine2 or me3 with EAC disabled the community norm.
• Valve's VAC bans modified clients on VAC-secured servers. The rule is to test locally with -insecure and never join public servers while anything is injected.
• No game files or decompiled code in a released mod. Mods ship as code, your own assets, patches or converters.
• Backups before saves are touched, processes killed only by exact process ID, and a confirmation before input automation, loader installs or publishing.

These are instructions the agent reads and follows, not a technical lock. No refusal was tested, and you still decide which game to point the agent at. The safety file also says "None of this is legal advice" and cites takedowns that happened even without shipped game assets: Take-Two against the re3 and reVC projects in 2021, and Activision's cease-and-desist to the H2M mod in 2024.

One rule does have a tool behind it. um publish check scans a mod folder before release, and with --game pointing at the game's install folder it also looks for copied game files. On a test folder with a .env file holding a fal key, it blocked the release:

Ran (test folder):

$ um publish check mymod
FAIL  env file (secrets?): .env
FAIL  FAL_KEY assignment in .env
WARN  no README (install steps, requirements, credits)
FAIL: 3 files, 2 failures, 1 warnings

Run it before you share anything, especially if your fal key ever sat in a .env file inside the mod folder.

Universal Modder FAQ: price, Codex, Minecraft

Is Universal Modder free?

The code is free under the MIT license. Using it isn't. Claude Code needs a Pro, Max, Team, Enterprise or Console account, and fal bills per generation, about $0.211 for one sprite at um's default quality as of October 6, 2026. Without a fal key, um comfy can make images through a local ComfyUI server.

Does Universal Modder work with Codex?

The README lists a Codex route: codex plugin marketplace add rehan-remade/universal-modder, then codex plugin add universal-modder@universal-modder. Codex gets the same skills, fal MCP server and um CLI. The October 6 test covered only the Claude Code install, so the Codex route is untested.

Can Universal Modder make Minecraft mods?

Minecraft has its own playbook in the mod-any-game skill, and the GTA V example includes a Fabric mod for Minecraft. The README also links community field notes on Halo 3 weapons and vehicles ported into Minecraft, Bloons TD 6 inside Minecraft, and real Minecraft running inside Portal 2. Those are community claims; no Minecraft mod was built in the October 6 test.