build123d

build123d-claude-plugin

A Claude Code plugin and MCP server for creating 3D CAD models using build123d, a Python parametric CAD library built on the OpenCascade kernel.

Features

• AI-assisted CAD modeling — Claude writes build123d code, executes it, and exports artifacts
• MCP server with 7 tools for the full CAD workflow:
  • execute_build123d — Run build123d code to create 3D models
  • export_stl — Export to STL (for 3D printing)
  • export_step — Export to STEP (for CAD interchange)
  • render_image — Render PNG/SVG images from multiple view angles
  • list_models / get_model_info / delete_model — Session management
• Sandboxed execution — Code runs in a restricted namespace (imports limited to an allow-list, dangerous builtins removed). This is best-effort hardening, not a hard security boundary.
• CLAUDE.md reference — Comprehensive build123d API guide for Claude

Installation

pip install -e .

Dependencies

• Python 3.10+
• build123d (and OpenCascade via cadquery-ocp)
• mcp (Model Context Protocol SDK)
• CairoSVG — required for PNG rendering (needs the native Cairo library installed on your system)
• Pillow — used as a placeholder fallback if CairoSVG is unavailable

Setup with Claude Code

As a plugin

This repository ships a .mcp.json that launches the server from the plugin's own bundled source via uv:

{
  "mcpServers": {
    "build123d": {
      "command": "uvx",
      "args": ["--from", "${CLAUDE_PLUGIN_ROOT}", "build123d-mcp"]
    }
  }
}

${CLAUDE_PLUGIN_ROOT} resolves to the plugin's install directory, so this always runs the code in this repo (and its pinned dependencies) rather than a same-named package from PyPI.

Standalone MCP server

If you've installed this package into an environment yourself (pip install -e .), point Claude Code at the installed console script:

{
  "mcpServers": {
    "build123d": {
      "command": "build123d-mcp",
      "args": ["--output-dir", "./cad-output"]
    }
  }
}

Usage

Once configured, ask Claude to create CAD models:

"Create a box with rounded edges, 40x30x20mm with 3mm fillets"

"Design a parametric enclosure for a Raspberry Pi with screw mounting holes"

"Make an L-bracket with mounting holes and export it as STL for 3D printing"

Claude will:

1. Write build123d code using the execute_build123d tool
2. Show you model properties (size, volume, topology)
3. Render images with render_image
4. Export to STL/STEP when you're ready

Project Structure

├── CLAUDE.md                      # Build123d reference for Claude
├── pyproject.toml                 # Python package config
├── src/build123d_mcp/
│   ├── server.py                  # MCP server & tool definitions
│   ├── executor.py                # Sandboxed code execution engine
│   ├── exporter.py                # STL/STEP export + model properties
│   └── renderer.py                # SVG/PNG image rendering
├── examples/                      # Example build123d scripts
│   ├── simple_box.py
│   ├── enclosure.py
│   └── bracket.py
└── tests/                         # Unit tests

Running Tests

pip install -e ".[dev]"
pytest

Security

The code executor applies best-effort hardening (not a hard security boundary):

• Allowed imports: build123d, math, typing, collections, itertools, functools, dataclasses, enum — enforced at both AST-validation time and runtime (via a constrained __import__). build123d and math are also pre-imported, so most code needs no import at all.
• Blocked builtins: open, exec, eval, compile, exit, input, getattr/setattr, and others are removed from the namespace.
• AST validation: disallowed imports and dunder attribute access are rejected before execution.
• Timeout: 60-second execution limit (via SIGALRM on the main thread, falling back to a subprocess where signals are unavailable).

License

MIT