CAD MCP Server

CAD MCP Server

An MCP server that measures STEP CAD files for an AI assistant: overall size and volume, hole and boss diameters, wall thickness, clearance, draft, cross-sections, and differences between two revisions. Measurements are computed by the Open CASCADE kernel from the model's own geometry.

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, including Claude Desktop, Cursor, and VS Code.

Example prompts

• "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 and report it in millimetres."
• "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 are millimetres and angles are degrees.

Results are reproducible: the server returns the entity IDs and the SHA-256 revision each measurement came from, and rejects stale IDs when a file changes underneath a session. It reports geometry; whether a part is manufacturable remains an engineering judgment.

Requirements

• Node.js 24+
• 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.

Documentation

• Example prompts
• Architecture — tools, workflow, and limits
• Security — local processing and handling CAD files as sensitive input
• Development — source setup, checks, packaging, and releases
• Changelog

License

MIT. The bundled Open CASCADE sidecar uses LGPL-2.1. See THIRD_PARTY_NOTICES.md.