Fusion MCP

Your agent can design a part from scratch in Autodesk Fusion, export it, and hand the STL to the slicer and printer tools in this server. Fusion keeps the design parametric, so a later change ("make it 1 mm wider") can be a single parameter edit instead of a new mesh.

This server does not bundle Fusion. It connects as an MCP client over stdio to faust-machines/fusion360-mcp-server (MIT), which talks over TCP to that project's Fusion360MCP add-in running inside Fusion. Fusion and its licence, including Autodesk's free personal-use licence, are yours. Printer tools work without Fusion configured. Scan cleanup and touch-ups still use Blender.

Set it up

The server and the add-in are pinned to commit 86a3016a5a5b of DMontgomery40/fusion360-mcp-server: faust-machines' server and add-in with document binding, while that change is reviewed upstream (bambu-printer-mcp pins the same commit). The PyPI release (0.1.0) crashes under mcp 2.x (issue #30), and the pinned commit keeps mcp>=1.0,<2.

On macOS, fusion_mcp_setup does steps 2 and 3 and the port login item below. Without arguments it reports, changing nothing: whether Fusion is installed, whether the add-in is at the pin and runs on startup, whether the login item is installed and whether this server has its Fusion settings. With {"install": true} it downloads the pinned commit's archive, checks every add-in file against its SHA-256 (a symlink, an extra file or a changed byte installs nothing), installs it set to run on startup (an add-in already at the pin is left in place), loads a login LaunchAgent, com.scantomake.mac.fusion-port, that runs launchctl setenv FUSION_MCP_PORT 9877, and adds the settings this server is missing to its own .env after a copy of the file. A setting the server or its .env already has is never rewritten. It never starts or quits Fusion.

1. Install Autodesk Fusion and uv.

2. Install the add-in from the same commit: copy the repository's addon/ folder at 86a3016a5a5b to ~/Library/Application Support/Autodesk/Autodesk Fusion 360/API/AddIns/Fusion360MCP. In Fusion, open Utilities → Add-Ins → Scripts and Add-Ins, select Fusion360MCP, and turn on Run on Startup.

3. Give this server its settings, in the same env file as BLENDER_MCP_* (your agent can do this during setup):

   Variable	Value
   FUSION_MCP_COMMAND	The full path to uvx
   FUSION_MCP_ARGS	["--from","git+https://github.com/DMontgomery40/fusion360-mcp-server@86a3016a5a5b","fusion360-mcp-server","--mode","socket"] (the default when unset)
   FUSION_MCP_TIMEOUT_MS	Optional, default 180000. The first start downloads the pinned server
   FUSION_MCP_HOST	Optional, default localhost. Passed through to the Fusion server
   FUSION_MCP_PORT	9877 (the default). Blender's MCP addon holds 9876, the add-in's own default

   The bridge passes FUSION_MCP_PORT to the Fusion server, but the add-in reads it from Fusion's environment, and an app opened from the Dock gets no shell environment. fusion_mcp_status with launch: true opens Fusion with open -a "Autodesk Fusion" --env FUSION_MCP_PORT=9877. To open it yourself on that port, run launchctl setenv FUSION_MCP_PORT 9877 once per login, then start Fusion.

4. Open Fusion and open or create any design once (File → New Design); see the bootstrap gap below.

Check it: ask your agent to call fusion_mcp_status. connected: true means the Fusion server started and the add-in answered.

How the pieces fit

Step	Tool	What it does
Check Fusion	fusion_mcp_status	{configured, connected, addinReachable, fusionRunning, tools[], launched, pin, server, error}. launch: true opens Fusion on this Mac when it isn't running and waits up to 90 s for the add-in
Start a design	fusion_mcp_new_design	Opens a new parametric design document through execute_code
Model	fusion_mcp_call	Forwards any of the server's 93 tools: create_sketch, extrude, revolve, create_hole, create_thread, fillet, shell, boolean_operation, create_parameter, set_parameter, check_interference, execute_code, …
Export	fusion_mcp_export	Writes <name>.stl, <name>.f3d and <name>.parameters.json into output_dir and returns their absolute paths as stl, f3d and parameters
Check and print	get_stl_info, lay_flat, slice_stl, …	The usual path, with every print safety check

fusion_mcp_status checks the add-in by sending it the protocol's ping over TCP and requiring its pong within a 2 s hard deadline, so another program on the port (such as Blender's addon) is not mistaken for Fusion. fusionRunning comes from the Fusion process on macOS. Elsewhere, or when FUSION_MCP_HOST is another computer, it is whether the add-in answered.

fusion_mcp_export exports one body as the STL: the only visible solid body, or the one named in body_name. export_stl picks the first body with that name, hidden or not, so the name must be unique across every body, including hidden ones and copies of an instanced component; otherwise rename it in Fusion. It stages the files, checks that Fusion wrote them, validates the STL as a finite triangle mesh, and only then publishes all three. Existing files are never overwritten, and on any failure nothing is left behind. The parameters file holds the design's user parameters (name, value, expression, unit, comment), read through execute_code, because get_parameters returns its result as Python text rather than JSON. Fusion and this server must share the file system, so keep FUSION_MCP_HOST local for exports.

Units. Fusion works in centimetres internally, and most tools take lengths in centimetres. STL files carry no units and slicers read them as millimetres. fusion_mcp_export compares the STL's size with the Fusion body's size and reports stlUnits (mm, cm, or unknown) and the body's fusionSizeMm. If the STL came out in centimetres, the result warns you to scale it by 10 before slicing. Compare boundingBox.dimensions with what you asked for before printing.

The bootstrap gap (issue #12)

At the pinned commit every Fusion tool, including execute_code, needs an active design. When Fusion sits on its home screen with no document open, no tool can create the first one (issue #12). fusion_mcp_new_design works once any design is open; on the home screen it fails with instructions to open or create a design once in Fusion. The fix proposed upstream lets execute_code run without a design; move the pin only after it lands and the acceptance check below passes.

Check a Fusion install end to end

PRD §8.9's acceptance check, run on a Mac with Fusion before the pin moves:

1. Start a "make something that fits" pass for a dimensioned bracket.
2. fusion_mcp_export returns STL, F3D and parameters.
3. get_stl_info matches the requested dimensions within ±0.2 mm.
4. A follow-up that changes one dimension by 1 mm is a single set_parameter, and the re-export matches within ±0.2 mm.
5. slice_stl succeeds on the P1S profile.

Evidence for this release: the pinned server was started through this bridge with uvx and listed its 93 tools, and the bridge's tests run against a stdio peer that reproduces that commit's recorded output. The acceptance check above has not been run here, because Fusion was not installed on the test Mac.

Safety and limits

• fusion_mcp_call can change your open Fusion design. Calls are never retried automatically; after a timeout, look at Fusion before trying again, because the request may still have run.
• Fusion executables come only from server configuration. No tool accepts an executable or command argument.
• Printer access codes and other server secrets are not passed to the Fusion server process; only FUSION_* settings are.
• The client stays connected for the life of this server, so the Fusion server starts once. If it exits, the next call starts it again.
• measure_distance is broken at the pinned commit (issue #27). Measure the exported STL with get_stl_info instead.
• A valid STL is not a guarantee of a good print. Check the reported dimensions, slice it, and look at the preview before printing.