Fusion Toolsmith MCP

Safety-first Autodesk Fusion 360 MCP add-in for agents that need to inspect, plan, validate, and package CAD changes without blindly running raw scripts.

Fusion Toolsmith MCP runs inside Fusion 360, exposes MCP over local HTTP/SSE on port 9100, and writes live discovery data to ~/.fusion_mcp.json. The add-in is opt-in by default and does not start automatically with Fusion.

The installed Fusion add-in folder is still named FusionMCP for compatibility with existing local installs.

Toolsmith inspecting a live Fusion model, applying a structured parameter edit from toolsmithWidth = 42 mm to 56 mm, validating the before/after state, and passing export preflight.

Why Toolsmith

Generic Fusion MCP servers often expose a raw script bridge. Toolsmith adds a disciplined CAD workflow around that bridge:

• Inspect the live model before editing.

• Map sketches, features, parameters, projected geometry, and downstream dependencies.

• Route agents through structured tools before raw Fusion API scripts.

• Preflight exports and model mutations.

• Keep dangerous tools separated from normal inspection/modeling workflows.

• Record a local redacted tool-call journal.

Use Toolsmith when you want an agent to behave like a careful CAD assistant, not just a Python executor.

Related MCP server: Fusion 360 MCP

What It Is Good At

• Inspecting existing designs before editing: sketches, features, parameters, projected geometry, selections, dependency reports, and coordinate mapping.

• Safer model mutation: explicit operations, preflight checks, downstream-consumer warnings, before/after design-state comparisons, and validation tools.

• Export safety: preflight-gated STEP/STL/PDF workflows.

• Local runtime hardening: fixed port, bearer-token support, token-free /health, session TTL cleanup, single active SSE client, and automatic Antigravity config sync.

Runtime Shape

MCP client
  -> http://127.0.0.1:9100/sse
  -> FusionMCP add-in running inside Fusion 360
  -> Fusion API on Fusion's main thread

Discovery file:

C:\Users\<you>\.fusion_mcp.json

The discovery file includes:

• sse_url: legacy query-token URL for clients that only support URL auth.

• bearer_sse_url: preferred token-free URL.

• authorization_header: preferred bearer auth header.

• port and token.

Install From This Checkout

Detailed installation and troubleshooting notes are in docs/installation.md.

Install the management CLI in editable mode:

python -m pip install -e .

Install or refresh the Fusion add-in files:

fusion-mcp install-addin

Build a distributable add-in ZIP:

fusion-mcp package-addin

The package is written to:

dist\FusionMCP-addin.zip

Then start or restart the FusionMCP add-in from Fusion 360:

Utilities > Add-Ins > Scripts and Add-Ins > Add-Ins > FusionMCP > Run

The manifest keeps runOnStartup set to false. Start the add-in only when you need it.

Verify

Run the live smoke test:

fusion-mcp test-live

Or use the PowerShell script directly:

powershell -ExecutionPolicy Bypass -File scripts/test_fusion_mcp_live.ps1

Check runtime health:

Invoke-RestMethod http://127.0.0.1:9100/health | ConvertTo-Json

Expected health output includes discovery, active_sessions, active_http_sessions, task_manager_running, and pending_tasks. It should not include a token or sse_url.

Client Config

Print both legacy and bearer-style client snippets:

fusion-mcp print-client-config

For Antigravity/Gemini-style config, FusionMCP auto-syncs this file on add-in startup:

C:\Users\<you>\.gemini\config\mcp_config.json

Manual sync is still available:

fusion-mcp sync-config

Tool Profiles

Machine-readable profiles are available through both the CLI and MCP resource layer:

fusion-mcp list-profiles

fusion://agent/tool-profiles

Use these mental profiles when exposing tools to agents or documenting workflows:

• core: doctor, get_runtime_diagnostics, get_change_journal, recommend_mcp_workflow, get_best_practices.

• inspection: inspect_design, capture_design_state, compare_design_state, inspect_sketch, inspect_feature, get_dependency_graph, query_selection.

• modeling: create_sketch, draw_line, draw_rectangle, draw_circle, project_geometry, extrude_feature, fillet_feature, chamfer_feature, combine_bodies.

• parameters: get_parameter, set_parameter, modify_parameters, plan_parameterization, get_parameter_usage.

• export: preflight_export, export_asset, create_2d_drawing.

• docs: search_local_fusion_docs, get_fusion_api_help, search_fusion_api_documentation, get_mcp_workflow_guide, get_best_practices.

• dangerous: run_fusion_script, clear_change_journal, document activation/revert tools, delete/suppress tools. Use only after structured tools are insufficient.

Development

Run the unit suite:

python -m unittest discover -s tests

Run the structural live fixture when FusionMCP is loaded and you want deeper end-to-end coverage:

powershell -ExecutionPolicy Bypass -File scripts/test_fusion_mcp_inspection_fixture.ps1

Useful starter prompts are in examples/prompts.md.

Use docs/demo-script.md to record the short demo GIF/video for the README.

CI And Releases

GitHub Actions runs the unit suite and builds the add-in ZIP on pushes and pull requests.

To publish a GitHub release with the packaged add-in attached:

git tag v1.0.0
git push origin v1.0.0

License

MIT. See LICENSE.

Change Journal

FusionMCP writes local JSONL tool-call audit entries to:

C:\Users\<you>\.fusion_mcp\journal.jsonl

Read it through MCP:

fusion://runtime/change-journal

Or call:

get_change_journal
clear_change_journal

The journal redacts tokens, authorization headers, raw scripts, and long string arguments.

Local Docs

FusionMCP exposes a local Fusion API and best-practices index:

fusion://docs/fusion-api

Search it with:

search_local_fusion_docs

This is an offline companion to official Autodesk docs and is meant for quick planning before writing raw Fusion API scripts.

Safety Notes

• Fusion API calls must execute on Fusion's main thread through TaskManager.

• run_fusion_script is intentionally a last-resort tool and requires intent/gap fields.

• Query-token auth remains for legacy clients, but bearer auth is preferred.

• If behavior does not change after editing files, reload the add-in or restart Fusion; Fusion may still hold the old Python modules in memory.