dcc-mcp-unity 0.4.1

Unity Editor adapter and typed game-authoring skills for DCC-MCP

dcc-mcp-unity

Unity Editor adapter for the DCC Model Context Protocol ecosystem. It ships a UPM Editor package, a loopback WebSocket bridge, and typed project and scene tools.

The supported Editor range starts at Unity 2018.4.25f1 with the .NET 4.x Equivalent scripting runtime. CI pins that Unity 2018 baseline, the 2021.3 baseline, and the current stable Unity 6 release instead of using a drifting latest tag.

The first-release boundary and comparison with unity-cli and two established Unity MCP projects are documented in the architecture benchmark.

Install

pip install dcc-mcp-unity
dcc-mcp-unity-install /path/to/UnityProject

Open or restart the Unity project so Package Manager compiles DCC-MCP Unity, then run:

dcc-mcp-unity

See the installation guide for upgrade, environment, and connection verification details.

The MCP endpoint uses a free loopback port and is registered for gateway discovery. Set DCC_MCP_UNITY_PORT=8765 before starting the server only when a fixed direct endpoint is needed. The Editor package reconnects to the loopback bridge at ws://127.0.0.1:3852; set DCC_MCP_UNITY_BRIDGE_PORT before the MCP server and DCC_MCP_UNITY_BRIDGE_URL before Unity starts to override it. DCC_MCP_UNITY_BRIDGE_TIMEOUT may increase the 60-second RPC timeout but cannot lower it; queued Editor work expires first so timed-out mutations are not executed later.

The default bridge targets one Unity Editor. For concurrent Editors, run one adapter per Editor and assign each pair a unique bridge port and URL before starting either process.

Standalone sidecar

Hosts without an embedded Python runtime can use the PyOxidizer sidecar released with each version. The release asset contains the executable, its adjacent lib/ runtime, and SHA256SUMS. Configure the Unity package to start it on editor load by setting DCC_MCP_UNITY_SIDECAR_PATH; optionally set DCC_MCP_UNITY_SIDECAR_SHA256 to the published digest. The launcher is loopback-only, passes the Unity process id to --watch-pid, and uses a per-project pid file to avoid duplicate sidecars after assembly reloads.

For local development, run dcc-mcp-unity-standalone --bridge-port 3852 --watch-pid <unity-pid>.

Agent workflow

1. Load unity-project and call inspect_project before assuming project or editor state. Stop if the returned project is not the intended target or the Editor is compiling, updating, entering Play Mode, or playing.
2. Load unity-scene and call inspect_scene immediately before using an instance ID. Treat IDs as opaque values and return them unchanged. Unity 6000.5+ emits decimal strings; older Editors retain integer output, and both forms are accepted as input.
3. Create GameObjects or change transforms through typed operations backed by Unity Undo.
4. Verify the hierarchy, then explicitly call save_scene.
5. Load unity-diagnostics and call read_console after failures or as a final verification step.

Do not automatically retry a timed-out scene mutation. Inspect the project and scene first because the Editor may have completed the original request near the timeout boundary.

No raw C# evaluation, shell command, or arbitrary filesystem write is exposed. The Editor bridge accepts only the methods implemented in DccMcpCommands and executes them on Unity's editor update loop. Mutations fail closed during compilation, asset updates, and Play Mode. Requests, queued work, scene snapshots, Console reads, and serialized responses have explicit size or lifetime budgets.

Validation boundary

Public CI validates Python 3.9 and 3.12 on Windows, macOS, and Linux; validates the bundled skill contracts; performs static checks for the UPM package and main-thread/Undo contracts; and builds the PyPI artifacts. Trusted pull requests, main, and the weekly schedule also compile the UPM package and run its command, scene, Undo, and validation tests through GameCI in Unity 2018.4.25f1, 2021.3.45f1, and 6000.5.4f1. Fork pull requests skip the licensed Editor jobs because GitHub does not expose repository secrets to forks. Licensed runs share one repository-wide queue across pull requests, main, releases, and schedules so a Personal seat is never activated concurrently. Each Editor also completes a real WebSocket hello → project.inspect → response smoke against the Python sidecar and records the reported Editor version as an artifact.

Development

uv sync --extra dev
uv run python -m pytest
uv run ruff check src tests tools
uv run ruff format --check src tests tools
uv run python tools/lint_skills.py
uv run python -m build
uv run python -m twine check dist/*

Unity and the Unity cube logo are trademarks of Unity Technologies. This independent adapter is not affiliated with or endorsed by Unity Technologies.