Build123d MCP服务器

build123d-mcp

An MCP (Model Context Protocol) server that exposes build123d CAD operations as tools, enabling AI assistants to build, inspect, and iterate on 3D geometry interactively.

Installation

No clone needed. Install directly from PyPI:

pip install build123d-mcp

Or just use uv tool run — it fetches and runs the package in one step with no prior install required (see below).

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Recommended workflow

Build complexity falls into two tiers and the right approach differs between them.

Simple shapes (a few primitives, up to ~5 booleans): build entirely in execute().

Complex shapes (IsoThread, multi-body fillets, high face counts): the execute() timeout (default 120 s) is a hard ceiling. The efficient pattern is:

1. Probe in the MCP — small execute() calls to discover API signatures, size strings, and face counts. Use dir() and import inspect; inspect.signature(ClassName) freely. 2. Build in a Python script — run it with Bash (or your shell). No timeout, full Python. 3. Import and verify in the MCP:

   import_cad_file("/path/to/part.step", "part")
   measure("part")          # verify volume, topology, bounding box
   render_view(objects="part")  # visualise
   

Timeout note: the default is 120 s. Raise it with --exec-timeout N or BUILD123D_EXEC_TIMEOUT=N. When a timeout fires, all session state is lost (worker is restarted) — you must re-run any setup code.

Sandboxed-host note: if every execute() fails with "Worker process failed to start", your MCP host is likely blocking subprocess creation (seen with sandboxed hosts on Windows). Relaunch with --in-process or BUILD123D_IN_PROCESS=1 — a degraded mode that runs the CAD session inside the server process: no crash containment, no operation timeouts.

Import note: after import_cad_file() the shape is a named session object. Always render it by name (objects="part") when other shapes from the same build are also in session — two co-located shapes cause Z-fighting (striped colour artifacts). STL imports produce a shell (volume = 0); render_view and measure work, but clearance() and boolean operations require a solid.

VS Code (GitHub Copilot / Continue)

For Continue extension, add to .continue/config.json:

{
  "mcpServers": [
    {
      "name": "build123d-mcp",
      "command": "uv",
      "args": ["tool", "run", "--python", "3.12", "build123d-mcp@latest"]
    }
  ]
}

For GitHub Copilot with MCP support, add to .vscode/mcp.json in your workspace:

{
  "servers": {
    "build123d-mcp": {
      "type": "stdio",
      "command": "uv",
      "args": ["tool", "run", "--python", "3.12", "build123d-mcp@latest"]
    }
  }
}

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