pzfreo/build123d-mcp

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.

Why

When using an AI to write build123d scripts, the AI writes blind — it cannot see the geometry it produces. This server closes the feedback loop: the AI can create geometry, render views, query dimensions, and catch errors incrementally rather than writing complete scripts and hoping they are correct.

Tools

Core

• execute — run build123d Python code in a persistent session; use show(shape, name) to register named parts
• reset — clear session back to empty state (namespace, shapes, snapshots)

Geometry inspection

• measure — full geometric summary: volume, area, topology, bounding box, centre of mass, inertia tensor, face-type inventory
• clearance — minimum distance (mm) between two named shapes
• cross_sections — cross-sectional areas at evenly spaced planes along X/Y/Z; useful for detecting voids and wall-thickness variation
• session_state — full JSON snapshot of active shapes, named objects, snapshot names, and Python namespace variables
• last_error — details of the last failed execute(): type, message, line number, and code excerpt

Viewing

• render_view — render one or more shapes as PNG / SVG / DXF; auto-detects 3D vs 2D inputs (compos