unity-api-mcp

MCP server that gives AI agents accurate Unity API documentation. Prevents hallucinated signatures, wrong namespaces, and deprecated API usage.

Supports Unity 6 (one database per minor stream), Unity 2023, and Unity 2022 LTS. Works with Claude Code, Cursor, Windsurf, or any MCP-compatible AI tool. No Unity installation required. See the supported versions. New Unity releases are detected and built automatically every week.

Quick Start

Add to your MCP config (.mcp.json, mcp.json, or your tool's MCP settings), setting UNITY_VERSION to match your project:

{
  "mcpServers": {
    "unity-api": {
      "command": "uvx",
      "args": ["unity-api-mcp"],
      "env": {
        "UNITY_VERSION": "6000.3"
      }
    }
  }
}

Valid values: a Unity 6 stream like "6000.3", or "6", "2023", "2022".

On first run the server downloads the correct database (~20-30 MB) to ~/.unity-api-mcp/.

How It Works

1. Version detection. The server figures out which Unity version to serve:

2. Database download. If the database for that version isn't cached locally, it downloads from GitHub. Unity 6 minor streams (6000.0, 6000.3, 6000.5, …) get their own per-stream database, falling back to the generic 6 database when a stream database isn't published. Cached databases are freshness-checked against the release on startup, so weekly rebuilds reach existing installs automatically.

3. Serve. All tool calls query the version-specific SQLite database. Every query returns in <15ms.

Each version has its own database with the correct signatures, deprecation warnings, and member lists for that release.

Tools

Coverage

All UnityEngine and UnityEditor modules, plus packages parsed from C# source: Input System, Addressables, uGUI (incl. TextMeshPro on Unity 6), AI Navigation, and Netcode. ~42,500 records per Unity 6 database, ~500 deprecation warnings each.

Full version list: db-v1 release page. CI regenerates that table on every build. New Unity patches are detected and built automatically every Monday.

Does not cover third-party assets (DOTween, VContainer, Newtonsoft.Json). For those, rely on project source.

Benchmarks

Measured, not promised: 25 research questions across 3 testbeds, answered by 3 agent configs, every answer judged against ground truth verified in the source beforehand. The full harness lives in docs/benchmark/ and re-runs with one command.

The one reproduced hallucination is instructive. Asked to list the overloads of SceneManager.LoadSceneAsync, both non-MCP agents invented single-parameter LoadSceneAsync(string) and LoadSceneAsync(int) overloads that do not exist. Code written against them does not compile. The MCP agent returned the exact four real overloads.

Why correctness and not token savings? Agentic tools are good at code search now. Claude Code has shipped a Grep tool from the start, and current models search first and then read a narrow line range, so raw token use was comparable across all configs in our runs. But exact overloads, namespaces, and deprecations are not in your project files at all. An agent without MCP can only infer them from usage examples, and when it infers wrong you pay with a broken build.

• 3 testbeds: a real Unity 6 game project (11 questions), pure Unity API lookups (8), and Unity Input System package source with 2,700 to 4,600 line files (6)
• 3 configs, same model and turn limit: MCP tools + Grep/Read, Grep/Read only, Read only
• Ground truth verified by reading the source before any runs; answers judged by a separate model session against that ground truth; token usage taken from API usage fields
• Run it yourself: python docs/benchmark/run.py --project <unity-project-path> (results from July 2026; agent behavior moves, so re-run before quoting)

CLAUDE.md Snippet

Add this to your project's CLAUDE.md (or equivalent instructions file). This step is important. Without it, the AI has the tools but won't know when to reach for them.

## Unity API Lookup (unity-api MCP)

Use the `unity-api` MCP tools to verify Unity API usage instead of guessing. **Do not hallucinate signatures.**

| When | Tool | Example |
|------|------|---------|
| Unsure about a method's parameters or return type | `get_method_signature` | `get_method_signature("UnityEngine.Tilemaps.Tilemap.SetTile")` |
| Need the `using` directive for a type | `get_namespace` | `get_namespace("SceneManager")` |
| Want to see all members on a class | `get_class_reference` | `get_class_reference("InputAction")` |
| Searching for an API by keyword | `search_unity_api` | `search_unity_api("async load scene")` |
| Checking if an API is deprecated | `get_deprecation_warnings` | `get_deprecation_warnings("FindObjectOfType")` |

**Rules:**
- Before writing a Unity API call you haven't used in this conversation, verify the signature with `get_method_signature`
- Before adding a `using` directive, verify with `get_namespace` if unsure
- Covers: all UnityEngine/UnityEditor modules, Input System, Addressables, uGUI/TextMeshPro, AI Navigation, Netcode
- Does NOT cover: DOTween, VContainer, Newtonsoft.Json (third-party)

Setup Details

Instead of setting UNITY_VERSION, you can point to your Unity project. The server reads ProjectSettings/ProjectVersion.txt automatically:

{
  "mcpServers": {
    "unity-api": {
      "command": "uvx",
      "args": ["unity-api-mcp"],
      "env": {
        "UNITY_PROJECT_PATH": "/path/to/your/unity-project"
      }
    }
  }
}

Using pip install:

pip install unity-api-mcp

{
  "mcpServers": {
    "unity-api": {
      "command": "unity-api-mcp",
      "args": [],
      "env": {
        "UNITY_VERSION": "6000.3"
      }
    }
  }
}

If you want to build a database from your own Unity installation instead of downloading:

# Install with ingest dependencies
pip install unity-api-mcp[ingest]

# Windows
python -m unity_api_mcp.ingest --unity-version 6000.3 --unity-install "D:/Unity/6000.3.8f1" --project "F:/Unity Projects/MyProject"

# macOS
python -m unity_api_mcp.ingest --unity-version 6000.3 --unity-install "/Applications/Unity/Hub/Editor/6000.3.20f1" --project "/path/to/UnityProject"

# Legacy versions
python -m unity_api_mcp.ingest --unity-version 2022 --unity-install "D:/Unity/2022.3.62f1"

Databases are written to ~/.unity-api-mcp/unity_docs_{version}.db by default.

If an AI agent is setting this up for you:

Add unity-api-mcp to my MCP config using uvx with UNITY_VERSION set to match my project, append the CLAUDE.md snippet from the README, and verify with get_namespace("SceneManager").

unity-api-mcp/
├── src/unity_api_mcp/
│   ├── server.py          # MCP server (5 tools)
│   ├── db.py              # SQLite + FTS5 database layer
│   ├── version.py         # Version detection + DB download
│   ├── xml_parser.py      # Parse Unity XML IntelliSense files
│   ├── cs_doc_parser.py   # Parse C# doc comments from package source
│   ├── unity_paths.py     # Locate Unity install + package dirs
│   └── ingest.py          # CLI ingestion pipeline
└── pyproject.toml

Databases are stored in ~/.unity-api-mcp/ (downloaded on first run).

Troubleshooting

See Also

unreal-api-mcp: same concept for Unreal Engine (C++), with weekly auto-built databases per UE version.

Contact

Need a custom MCP server for your engine or framework? I build MCP tools that cut token waste and prevent hallucinations for AI-assisted game development. If you want something similar for your team's stack, reach out.

fuatcankoseoglu@gmail.com

License

MIT