cad-mcp-server Server

Dokumentation

CAD MCP Server

Read-only CAD inspection for LLMs, zero install. Bundles a WebAssembly Open CASCADE 8.0 kernel so AI assistants can read, measure, and compare STEP files locally. Returns deterministic geometry facts — the LLM interprets engineering meaning.

Quick Start

npx -y cad-mcp-server

Add to your MCP client config (Claude Desktop, OpenCode, Cursor, etc.):

{
  "mcpServers": {
    "cad": {
      "command": "npx",
      "args": ["-y", "cad-mcp-server"]
    }
  }
}

Point the AI at any STEP or STP file on your local filesystem.

Use Cases

Who	What they ask
Mechanical lead	"Review this STEP file like a mechanical lead before release. What are the top design or manufacturing risks?"
Manufacturing engineer	"Build a first-pass CNC plan: likely setups, drilling directions, and cost-driving features."
QC engineer	"Create an inspection plan from the STEP file. What should we measure? What's missing?"
Procurement / sourcing	"Prepare an RFQ summary: part count, envelope, complexity drivers, and questions the supplier will ask."
Design engineer (revision)	"Compare Rev A and Rev B as an ECO review. What changed? What should be rechecked?"
Hobbyist / maker	"Can these parts fit on a 200 x 200 x 300 mm printer? What needs splitting or reorientation?"

MCP Tools (v0.2)

Tool	Purpose
`inspect_step`	First-pass overview: dimensions, volume, topology, principal axes, OBB, watertight check, PMI hints. Use this first.
`query_step`	Declarative query: filter/sort/group faces, edges, bodies, vertices, PMI, colors, layers, materials, assembly. Measure distances, fire ray tests, compute sections, compute curvature. Aggregate stats. One call replaces 5+ primitive round-trips.
`diff_step`	Compare two STEP files: metric deltas, topology changes, body-level changes, XDE-level changes.
`transact_step`	Multi-step pipeline when a single query isn't enough: "for each hole, ray-test in +Z, then keep ones that didn't come out the other side."

Design principle: Deterministic geometry only. No interpretation, no heuristics. The server measures; the LLM decides.

The seven primitives from the v0.1 surface (face search, edge search, entity lookup, PMI query, ray test, distance, coaxial grouping) are now expressible as query_step calls — for example, find_coaxial_cylinders becomes {entities: "faces", filter: {surface_type: "cylinder"}, group_by: ["axis"]}. See docs/EXAMPLE_PROMPTS.md for prompt patterns that work with this surface.

How It Works

STEP files are parsed locally by a stripped Open CASCADE Technology (OCCT 8.0) kernel compiled to WebAssembly. No data leaves your machine. No Docker, no cloud API, no CAD license.

Why CAD MCP Server?

Zero install. One npx command, no native CAD software, no licenses, no Docker, no cloud API.
Read-only. No geometry creation or modification.
Local-first. STEP files never leave your filesystem.
WASM performance. OCCT runs at near-native speed in a bundled WebAssembly kernel.
LLM-native. Structured JSON output designed for AI consumption. Every tool has defaults, enums, pagination, and descriptions written for LLM reasoning.
OCCT-native. Every computation uses OCCT built-in classes — no custom math where OCCT already provides it.

What It Is Not

Not a CAD editor — no geometry creation or modification.
Not a CAM system — no toolpath generation.
Not a manufacturability certifier — it provides evidence, not conclusions.
Not an AP242 PMI engine — PMI hints are lightweight and heuristic-based.
Not a feature-tree recovery tool — STEP is a boundary-representation format.

Good AI answers separate measured facts, assumptions, and engineering recommendations.

Requirements

Node.js 22 or newer
Local access to STEP/STP files

No Docker, Open CASCADE install, or native CAD application required.

Distribution

The npm package is minimal: compiled JS, bundled occt-wasm WASM kernel, and TypeScript declarations.

Contributing

See CONTRIBUTING.md for setup, testing, and PR guidelines.

License

MIT. The bundled occt-wasm backend uses Open CASCADE Technology (LGPL-2.1). See THIRD_PARTY_NOTICES.md.

Support

If CAD MCP Server saves you time, consider sponsoring development.