unity-api-mcp 2.0.2

MCP server providing ground-truth Unity API documentation (2022/2023/6) -- prevents AI hallucination of signatures, namespaces, and deprecated APIs

unity-api-mcp

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

Supports Unity 2022 LTS, 2023, and Unity 6 with separate databases for each version. Works with Claude Code, Cursor, Windsurf, or any MCP-compatible AI tool. No Unity installation required.

Quick Start

pip install unity-api-mcp

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": "unity-api-mcp",
      "args": [],
      "env": {
        "UNITY_VERSION": "2022"
      }
    }
  }
}

Valid values: "2022", "2023", or "6". On Windows, use unity-api-mcp.exe.

On first run the server downloads the correct database (~18-24 MB) to ~/.unity-api-mcp/.

How It Works

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

Priority	Source	Example
1	UNITY_VERSION env var	"2022", "6", or "6000.3.8f1"
2	UNITY_PROJECT_PATH	Reads ProjectSettings/ProjectVersion.txt, maps 2022.3.62f1 to "2022"
3	Default	"6"

2. Database download. If the database for that version isn't cached locally, it downloads from GitHub (one time).

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

Tool	Purpose	Example
search_unity_api	Find APIs by keyword	"Tilemap SetTile", "async load scene"
get_method_signature	Exact signatures with all overloads	UnityEngine.Physics.Raycast
get_namespace	Resolve using directives	"SceneManager" -> using UnityEngine.SceneManagement;
get_class_reference	Full class reference card	"InputAction" -> all methods/fields/properties
get_deprecation_warnings	Check if an API is obsolete	"WWW" -> Use UnityWebRequest instead

Coverage

All UnityEngine and UnityEditor modules, plus packages parsed from C# source: Input System, Addressables, uGUI, TextMeshPro, AI Navigation, and Netcode.

Version	Records	Deprecated	Modules	Size
Unity 2022 LTS	32,000	442	86 XML + packages	18 MB
Unity 2023	31,387	436	92 XML	18 MB
Unity 6	42,223	516	139 XML + packages	24 MB

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

Benchmarks

In a 10-step research workflow, MCP uses 4x fewer tokens than a skilled agent and 11x fewer than a naive agent:

The gap holds across every question type. MCP wins on simple lookups and complex multi-part research alike:

Even in a realistic hybrid workflow where MCP results are followed up with targeted file reads, it still uses 54% fewer tokens than a skilled agent working without MCP:

"Without MCP" estimates assume full file reads. A skilled agent with good tooling may use fewer tokens than shown. What MCP guarantees is a correct, structured answer in 1 call every time.

Per-question breakdown

Accuracy

Test	Result
Search top-1 relevance (12 common queries)	100%
Namespace resolution (6 key classes)	100%
Key class coverage (17 common Unity classes)	94% (16/17)

Ranking uses BM25 with tuned column weights (member name 10x, class name 5x) plus core namespace boosting to ensure Object.Instantiate ranks above niche APIs like InstantiationParameters.Instantiate.

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
- Does NOT cover: DOTween, VContainer, Newtonsoft.Json (third-party)

Setup Details

Auto-detect version from project path

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

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

Environment variables

Variable	Purpose	Example
UNITY_VERSION	Unity version to serve	2022, 2023, 6, or 6000.3.8f1
UNITY_PROJECT_PATH	Auto-detect version from project	F:/Unity Projects/my-project
UNITY_INSTALL_PATH	Override Unity install path (for ingest only)	D:/Unity/6000.3.8f1

Building databases locally

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]

# Build for a specific version
python -m unity_api_mcp.ingest --unity-version 6 --unity-install "D:/Unity/6000.3.8f1" --project "F:/Unity Projects/MyProject"
python -m unity_api_mcp.ingest --unity-version 2022 --unity-install "D:/Unity/2022.3.62f1"
python -m unity_api_mcp.ingest --unity-version 2023 --unity-install "D:/Unity/2023.1.22f1"

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

AI-Assisted Setup

If an AI agent is setting this up for you:

Install unity-api-mcp via pip, add it to my MCP config with UNITY_VERSION set to match my project, append the CLAUDE.md snippet from the README, and verify with get_namespace("SceneManager").

Project structure

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

Problem	Fix
"Could not download Unity X database"	Check internet connection. Or build locally: python -m unity_api_mcp.ingest --unity-version 2022
Wrong API version being served	Set UNITY_VERSION explicitly. Check stderr: unity-api-mcp: serving Unity <version> API docs
Server won't start	Check python --version (needs 3.10+). Check path: which unity-api-mcp or where unity-api-mcp
Third-party packages return no results	DOTween, VContainer, Newtonsoft.Json are not indexed (third-party, not Unity packages)

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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.

[e-mail]

License

MIT