drawing-converter-mcp

Purpose

drawing-converter-mcp is an MCP (Model Context Protocol) server for converting technical drawings (PDF) and engineering annotations between metric and imperial units. It exposes the conversion engine behind metric-to-imperial-converter.imnoo.com (provided by Imnoo) to any AI assistant that supports MCP, enabling shop-floor-precision unit conversion covering dimensions, ± tolerances, ISO fit classes, threads, surface roughness, and weight, and can generate a converted PDF copy of the drawing, stamping each converted value at the original annotation position.

Main capabilities

• Convert engineering annotations in technical drawing PDFs, including dimensions, tolerances, ISO fits, threads, surface roughness, and weight.
• Generate a converted PDF copy with all converted values stamped at the original annotation positions.
• Provide the convert-drawing prompt, guiding the assistant through the "extract → classify → convert" workflow.
• Provide the extract_drawing_text tool, which hands every printed mark in the drawing and its position to the model.
• Provide the convert_drawing_pdf tool, which receives the model's classification of the marks and performs the conversion.
• Provide the convert_text tool, supporting quick single-line conversion, e.g. "How many inches is 84±0.1 mm?" → 3.3071±0.0039.
• Conversions follow the same rules as the Web app: exact internationally defined conversion factors are used (25.4 mm/in, 0.45359237 kg/lb, per NIST/ISO 80000); display rounding follows shop-floor conventions (a 0.01 mm step maps to 4 decimal places in inches, and tolerance deviations retain one extra significant digit).
• Threads are resolved using the ISO metric ⇄ UNC comparison table (M2–M30), marked as table (a row within the table) or nearest (matched by major diameter to the nearest). The tool states on every thread conversion that metric and imperial threads are not interchangeable.
• Each converted value reports how it was derived (exact / rounded / table / nearest) and a confidence score.

Usage

Requires Node.js ≥ 18. The server starts via stdio and can be added to any MCP client that supports stdio, for exampleExample:

• Claude Desktop: add to claude_desktop_config.json (Settings → Developer → Edit Config).
• Cursor: add to ~/.cursor/mcp.json.
• VS Code (GitHub Copilot).
• Windsurf or another stdio client.

Any client that can launch a stdio server can be used.

Example session:

User: Convert C:\drawings\flange.pdf to imperial. Assistant: Calls extract_drawing_text — 63 callouts, source system: metric (high confidence — "mm", ISO 2768). Classifies the callouts, skips the title block, marks the 1.6 next to the surface symbol as roughness, calls convert_drawing_pdf — writes C:\drawings\flange.imperial.pdf, converts 17 values: Ø40 H7 → Ø1.5748 H7, 2× M6 → 1/4-20 UNC (nearest standard — not interchangeable), Ra 1.6 → Ra 63 µin...

Quick one-liners work too: "How many inches is 84±0.1 mm?" → convert_text → 3.3071±0.0039.

When to use

• Manufacturing and engineering scenarios that need to convert metric technical drawings to imperial (or the reverse).
• Unit conversion of engineering annotations directly within an AI assistant.
• When a PDF copy stamped with converted values is needed for shop-floor use.

Limitations

• The PDF must contain a text layer. Scanned copies or flattened CAD exports have no text layer; the web app can handle these files through in-browser OCR + AI analysis, but this server does not provide that capability.
• Only one page is converted per call (page parameter, default 1); other pages are left as-is.
• Fractional-inch annotations (such as 1 3/4) are not currently supported for conversion; decimal-inch drawings are handled normally.
• Converted values are stamped over the original annotations. Always verify safety-critical dimensions before manufacturing.
• The AI analysis step is performed by the assistant; the server itself is fully deterministic and offline, requiring no API keys or cloud calls.

Other notes

This package is built from Imnoo's Drawing Converter monorepo and directly imports the web app's conversion engine, so the web app and this server produce identical conversion results by construction. Before each release, 31 end-to-end checks are run, which drive all five tools over stdio against generated sample drawings. Issues and feature requests are welcome in the repository.