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Configuration

Environment variables

Section titled “Environment variables”
Variable Default Purpose
MAX_FILE_SIZE_MB 100 Upper bound on input file size. Every file-reading tool checks it and returns a size error rather than loading an oversized file.
TEMP_DIR /tmp/cad_processing Scratch space for intermediate processing.
OUTPUT_DIR /app/output Where every tool that writes (conversions, renders, exports) puts its files. Tools return absolute paths under this directory.
FREECAD_PATH /usr/lib/freecad/lib Appended to sys.path so the FreeCAD Python modules import. Only relevant when running the FreeCAD tier outside the Docker image.

Directory fallback: if a configured directory can’t be created (the /app/* defaults outside a container, say), the server falls back to a per-user temp directory and logs a warning — rather than leaving every later export to fail mysteriously.

CLI

Section titled “CLI”

The cad-mcp-server console script (installed from pyproject.toml):

cad-mcp-server [--transport {http,stdio}] [--host HOST] [--port PORT]
Flag Default Notes
--transport http stdio for local subprocess clients
--host 0.0.0.0 HTTP transport only
--port 8000 HTTP transport only

The version banner and all diagnostics print to stderr; stdout is reserved for the JSON-RPC stream in stdio mode.

For development with hot reload, use the FastMCP CLI directly instead of the console script:

Terminal window
fastmcp run src/freecad_server.py:app --transport http \
  --host 0.0.0.0 --port 8000 --reload --reload-dir src

(The legacy --reload flag on cad-mcp-server exits with instructions to use the command above.)

Transports

Section titled “Transports”

stdio

Section titled “stdio”

Standard MCP subprocess transport. The client spawns the server and owns its lifecycle. See Getting started for the claude mcp add incantation.

HTTP

Section titled “HTTP”

The default. FastMCP serves the MCP endpoint at /mcp, and the server enables two options that matter for deployment:

  • json_response=True — plain JSON responses instead of SSE streams
  • stateless_http=True — no session ID required between requests

Together these keep remote clients (Claude’s remote connectors among them) working behind TLS-terminating reverse proxies, where SSE accept-header negotiation and sticky sessions are the classic failure points.

FreeCAD availability

Section titled “FreeCAD availability”

FreeCAD is probed at startup, not required:

  • Present — all 19 tools work. Core modules (Part, Mesh, Import) are all-or-nothing; optional workbenches (Draft, Sketcher, TechDraw, PartDesign, Assembly4, CAM, Arch, Material, the DXF importer) degrade individually, so one missing addon doesn’t poison the session.
  • Absent — the six DXF analysis tools work fully; FreeCAD-backed tools return a per-call error.

In Docker, FreeCAD is opt-in at build time via WITH_FREECAD=1 — see Run with Docker.