fusion-mcp-bridge

Fusion 360 via MCP-Bridge

A localhost HTTP bridge between Claude and Fusion 360, plus the small fusion CLI that wraps it. This skill documents the API patterns that recurrently fail without explicit guidance.

When to use

• Driving Fusion 360 geometry from a Claude session through the MCP-Bridge
• Writing Python scripts that will be executed via /execute against the bridge
• Debugging why a build script "ran" but produced no visible geometry change (silent-failure patterns)
• Recovering from a hung or unresponsive bridge

When NOT to use

• General Fusion modelling discussion → cad-construction
• General Python CAD scripting (OpenSCAD, FreeCAD) → cad-api-scripting
• Manufacturing or wall-thickness rules → mechanical-design-principles
• Brainstorming a design (no CAD work yet) → design-first-iteration

Setup

The bridge is a Fusion AddIn (<your-projects>/fusion360-mcp-bridge/fusion-addin/) that exposes three HTTP endpoints on 127.0.0.1:7654:

• GET /health — bridge alive + active document info
• POST /execute — body {"script": "<python>"} runs script in Fusion, returns {"result": "<stdout>"}
• POST /screenshot — body {"direction": "<dir>", "width": w, "height": h} returns {"screenshot": "<base64-png>"}

Bearer token from ~/.fusion-mcp-secret is required on all endpoints.

The fusion CLI wraps these endpoints. Always prefer the CLI over raw curl — it's shorter, error-handled, and consistent. Curl examples in this skill are fallbacks for when the CLI is unavailable.

fusion check                           # pre-flight
fusion run /tmp/build.py               # execute a script
fusion eval "print(1+1)"               # inline expression
fusion screenshot --direction front --out f.png
fusion components                      # list components + volumes
fusion volume "Hauptgehaeuse"          # specific body volume

Pre-flight protocol

Before every Fusion build session, run:

fusion check

This confirms: bridge alive, bearer token loaded, active document with a Design product. If any of these fail, the bridge will hang or scripts will silently no-op — fix the prerequisite first.