# Fusion360 MCP Server
## What this is
An MCP server that bridges Claude Code to Autodesk Fusion 360 for CAD automation. Two components:
1. **This repo** — Python MCP server (stdio transport, 80 tools). Claude talks to this.
2. **Fusion360MCP add-in** — installed in Fusion's AddIns folder. Listens on `localhost:9876`.
The MCP server receives tool calls from Claude, forwards them as JSON over TCP to the add-in, and returns results.
## Architecture
```
Claude Code ←(stdio MCP)→ This Server ←(TCP :9876)→ Fusion360MCP Add-in ←(CustomEvent)→ Fusion Main Thread
```
## Development
```bash
uv sync --dev # install deps
uv run pytest -v # run tests (245 tests)
uv run ruff check # lint
```
## Key files
- `src/fusion360_mcp/server.py` — MCP server entry point (click CLI), resources, prompts
- `src/fusion360_mcp/connection.py` — TCP client to Fusion add-in
- `src/fusion360_mcp/tools.py` — 80 tool definitions with annotations
- `src/fusion360_mcp/mock.py` — mock responses for `--mode mock` testing
- `tests/` — 245 tests covering tools, mock handlers, server routing, connection, annotations
## Adding a new command
1. Add the handler method in the **add-in's** `command_handler.py`
2. Add a tool definition dict in `src/fusion360_mcp/tools.py`
3. Add a mock handler in `src/fusion360_mcp/mock.py` + dispatch entry
4. Add tool name to the annotation sets if read-only/destructive/idempotent
5. Update `tests/test_tools.py` expected set and add mock test in `tests/test_mock.py`
6. The MCP server forwards tool calls 1:1 — no mapping code needed
## Conventions
- Tool names use snake_case and must match the add-in's command names exactly
- All Fusion API units are in **centimeters** (Fusion's internal unit)
- The add-in uses newline-delimited JSON over TCP
- `ping` is the health check — it never touches the Fusion API
- Every tool has annotations (`readOnlyHint`, `destructiveHint`, `idempotentHint`)
- Every tool has a mock handler so `--mode mock` works without Fusion running
