CAD MCP Server

Ottogeo — CAD MCP Server

[npm version] [npm downloads] [license] [CI]

Give any AI assistant the ability to measure real CAD geometry. The server opens STEP files with the Open CASCADE kernel and answers the questions an engineer actually asks — overall size and volume, hole and boss diameters, wall thickness, clearance, draft, cross-sections, and what changed between two revisions — with numbers computed from the model's own B-rep, not estimated from a screenshot.

[The assistant measures a pocket floor to cross-bore distance of 0.8 mm, sections the model to confirm it, and verifies 3.0 mm in the revised STEP file.]

Quick start

Add the server to your MCP client, then point your assistant at a STEP file:

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

Works with any MCP client — Claude Desktop, Cursor, VS Code, and the rest.

Ask it anything about a part

• "What are the overall dimensions and volume of this part?"
• "Find the cylindrical faces and list their diameters and axes."
• "Measure wall thickness on these faces."
• "What is the minimum distance between this hole and the nearest wall?"
• "Measure draft relative to the +Z direction and list faces with negative draft."
• "Cut a section through this body at X = 40."
• "What changed between revision A and revision B?"

More examples, including DFM-style review prompts, are in docs/EXAMPLE_PROMPTS.md.

Tools

Measurement kinds are distance, thickness, draft, ray, ray_grid, point_analysis, section, and continuity. Lengths come back in the file's declared unit, labelled on every result, so an inch model stays in inches and nothing has to be converted by hand. Angles are in degrees.

Why the numbers hold up

• Computed by Open CASCADE, not guessed. The same file and the same query return the same numbers, every time.
• Revision-bound and self-verifying. Every result carries the entity IDs and the SHA-256 revision it came from, and stale IDs are rejected when a file changes underneath a session — so an answer can never be attached to the wrong geometry.
• Reads the model's own callouts. describe_pmi reports the dimensions, geometric tolerances, and datums a file declares, each bound to the entities it applies to, so declared requirements can be checked against the geometry.
• Local and private. It runs over stdio and reads files by path. It is read-only and never uploads or writes your CAD data.

Requirements

• Node.js 26+
• Windows x64, macOS ARM64 (Apple Silicon), or Linux x64
• STEP files, as exported by SolidWorks, Fusion 360, Onshape, FreeCAD, CATIA, or any other CAD system

FAQ

Does it need CAD software installed? No. It reads STEP files directly, so it works on a machine without a CAD application or license.

Do my files leave my machine? No. The server runs locally over stdio and reads files by path. It is read-only and never writes to your CAD data.

How is this different from asking an assistant to look at a screenshot? Measurements are computed from the model's B-rep geometry by Open CASCADE, so the same file and query return the same numbers. Each result also carries the entity IDs and revision it came from.

Development

Source setup, checks, packaging, and releases are in docs/DEVELOPMENT.md. The server targets Windows x64, macOS ARM64, and Linux x64, and builds its native sidecar from the pinned OCCT revision.

Packaging

npm pack builds first and includes the compiled server, the native sidecar, this README, and the third-party notices. Tests and source maps are excluded. Install the tarball to check the cad-mcp-server executable with a compatible MCP client.

Documentation

• Example prompts
• Architecture — tools, workflow, and limits
• Security — local processing and handling CAD files as sensitive input
• Changelog

License

MIT. Third-party licenses: THIRD_PARTY_NOTICES.md.