Universal Modder + Claude Code: the complete setup

Why Claude Code is the reference agent

The project's author built the toolkit from real Claude Code sessions, and the repo ships Claude-specific wiring: a plugin marketplace (.claude-plugin/), skills copied to .claude/skills, the fal MCP server in .mcp.json, and a SessionStart hook that puts the umCLI on PATH every time a session starts or resumes. Other agents work too (see themulti-agent install guide), but Claude Code gets the most tested path.

1. Install Claude Code

Skip this if claude --version already works.

curl -fsSL https://claude.ai/install.sh | bash

irm https://claude.ai/install.ps1 | iex

Then make a working folder for your mods (for example ~/mods or C:\mods), runclaude inside it and sign in. You need a Claude Pro, Max, Team or Enterprise plan, or a Console account with API billing. If anything looks wrong, run claude doctor.

Also install the toolkit's prerequisites: Git, Python 3.10+, ffmpeg and uv (one-line installs).

2. Add the Universal Modder plugin

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

• Pick user scope so the plugin is available in every project folder.
• Run /reload-plugins if Claude Code asks, or restart the session.
• Prefer the shell? The same thing works as claude plugin marketplace add … and claude plugin install ….
• Getting an SSH error? See troubleshooting.

What the plugin installs

3. Connect fal for art, 3D and audio

The fal MCP server reads FAL_KEY from the environment Claude Code starts in. Create a key atfal.ai/dashboard/keys, export it, and restartclaude.

export FAL_KEY="your-key"     # macOS / Linux / WSL
setx FAL_KEY "your-key"       # Windows, then open a new terminal

Check it with /mcp inside Claude Code: the fal server should show as connected. Prices per asset are on the cost page.

Calling the skills

You rarely need to name a skill: a request like “mod Stardew Valley so…” loads mod-any-game, which pulls in the others as needed. To force one, type its slash command:

What each skill contains →

Prompts that work

Good prompts name the game, one concrete outcome, and what “done” looks like. Examples from the project README:

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

Make a new civilization for Age of Empires II with a unique unit rendered from 3D.

Put real Minecraft inside GTA V story mode. Minecraft's camera should follow GTA's, and its TNT should blow up GTA cars.

What engine is C:\Games\Foo, and has anyone modded it before?

Tips that save tokens and money:

• Recon first, build second. Ask for the plan before any change; it writes MODDING_PLAN.md.
• One slice at a time. A single working weapon beats ten half-built ones.
• Placeholders before fal. Generate final art only once the mechanic works in game.
• Ask for a price. “Check um fal price before generating the 3D model.”
• Hands off during tests. Don't use the PC while it drives the game or records.

Long projects and context limits

The skill keeps a journal in MODLOG.md (paths, IDs, formats, what failed, the next step), so nothing important is lost when Claude Code compacts the conversation. Start a fresh session with:

Read MODLOG.md and MODDING_PLAN.md and continue from the next step.

When the mod works, ask it to write a field note with the share-field-notes skill. It opens a pull request to the shared knowledge base only after you say OK.

What Claude Code has built with it

• Age of Empires II: Definitive Edition: San Franciscans: a new civilization for Age of Empires II DE with units rendered from 3D
• Baldur's Gate 3: Act 2 never loads (hang at 50% or crash): one modded NPC on a bad level layer, found by bisecting a pak
• Baldur's Gate 3: A generated wardrobe mod: 260 clothing mods sorted by race and body type into containers summoned by reusable scrolls
• Baldur's Gate 3: Custom outfits from cloned mod and vanilla meshes: visuals, materials, body masks, cloth, LODs, icons and the Blender GR2 round trip
• Baldur's Gate 3: Gameplay and compatibility patches in stats and Osiris: level-gated armour tiers, Extra Attack on a modded cantrip, crit immunity, stacking damage reduction, feats from items, removing equipment glow, a class vs starting-equipment fix
• Baldur's Gate 3: Running a 500+ mod load order by hand: modsettings.lsx rules, recovering a wiped order from a save, mod.io re-subscribes, game-folder files and conflict diagnosis
• Baldur's Gate 3: Weapons: porting a Skyrim dagger and scabbard, fixing a modded sword's sheath height with a Dummy_Sheath bone, and visible stowed shields for modded shields
• Borderlands 2: BL3 weapons and movement in Borderlands 2 (Willow2 SDK mods)
• Darkest Dungeon: A seeded randomizer (trinkets, heroes, monsters, curios, quirks, quests) as a Darkest Dungeon data mod
• Dragon's Dogma 2: Blink Strike teleports behind the target (REFramework Lua skill rework)
• Dragon's Dogma 2: Dimension Door: aimed teleport spell with a scripted arrival camera (REFramework Lua)
• Elden Ring: CS2 conversion of Elden Ring offline: native Rust DLL via me3 (fall death, spirit springs, 3D inspect, params)

Browse every game →