Free Unity AI Agent Rules (Cursor + Claude Code)

Free Cursor rules and an AGENTS.md that stop the most common AI coding mistakes in Unity C#. This is the free mini version of the Unity AI Agent Kit. MIT licensed, no account, no installs.

What it stops your AI doing

• Deleting or forgetting using lines (the #1 cause of CS0246 after an AI edit)
• Inventing Unity APIs that don't exist (GameObject.FindByTag, transform.GetChildByName, Rigidbody.AddVelocity...)
• Mixing Unity 6 and 2022.3 LTS APIs (velocity vs linearVelocity, drag vs linearDamping, obsolete FindObjectOfType)

What's inside

• 00-unity-core.mdc (always on): reads ProjectVersion.txt and manifest.json first, no invented APIs, writes complete files that compile
• 01-namespaces-usings.mdc: keeps your usings, with a type → namespace lookup table and name-clash fixes
• 04-unity-versions-api.mdc: Unity 6 vs 2022.3 LTS API table
• AGENTS.md: the same guidance for Claude Code, Codex and other agents
• PRIMING_HEADER.md: paste-in header for ChatGPT, Claude or Gemini chat
• START-HERE.txt: 1-minute install steps

How to install

Cursor: copy the .cursor folder and AGENTS.md into your Unity project root (next to Assets/). Cursor picks the rules up automatically.
Claude Code: copy AGENTS.md into the project root and add a CLAUDE.md containing the line @AGENTS.md (or just rename a copy to CLAUDE.md).
Chat tools: paste PRIMING_HEADER.md at the start of the conversation.
Test it: ask "Add a jump to PlayerController." It should read ProjectVersion.txt first and keep your using lines.
(.cursor is a hidden folder: Cmd+Shift+. in Finder on macOS, View > Show > Hidden items on Windows.)

Works with

Unity 6 and 2022.3 LTS · Cursor · Claude Code · ChatGPT / Claude / Gemini chat

Want the full kit?

The Unity AI Agent Kit adds 5 more rules (MonoBehaviour lifecycle, serialization, new Input System, performance, Unity Test Framework), a CLAUDE.md, a phased feature-planning workflow with templates, 20 task prompts (controllers, save/load, state machine, inventory, pooling, UI...) and a batchmode compile + EditMode test loop so your agent checks its own work before saying "done".
👉 Get it here: https://johnvanscoyoc.itch.io/unity-ai-agent-kit-rules-prompts-workflow-for-cursor-and-claude-code
Using Unity and Godot? Both kits together for $18: https://itch.io/s/205854/game-dev-ai-agent-kits-unity-godot

Source

Also on GitHub (issues and suggestions welcome): https://github.com/scoyoc5/unity-ai-agent-rules
Seen an AI invent a Unity API? Leave a comment with the fake call and the real one and I'll add it.

MIT license. Not affiliated with Unity Technologies, Anysphere (Cursor) or Anthropic.