cad-mcp-server Server

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.