SolidWorks MCP

Let an AI agent (Claude, or any other MCP client) model real parametric parts and assemblies in your own SolidWorks — and check its own work. Every modelling call returns the measured volume, mass and bounding box, so the agent can compare the result with the spec and correct itself instead of guessing that it "looks about right".

_{Built by the tools themselves: a mounting bracket (every step checked against a hand calculation), a revolved + shelled vase, a swept pipe.}

Why this server

• It verifies, not just generates. Features report measured geometry; dimensions and mates are measured back after the rebuild.
• Real CAD, not just primitives. Extrude, revolve, sweep, loft and splines; holes, counterbores, slots and pockets on any face; fillets, chamfers, shells, patterns, equations and materials. Assemblies with mates and interference checks. STEP/STL/3MF export and screenshots. 45 tools in total.
• It fails loud. A call that cannot do what was asked returns {ok: false, error} with the cause, never silently wrong geometry.
• A fixed, typed tool surface. There is no "run arbitrary code" tool; the agent can only do what the tools allow.
• Tested against real SolidWorks. 175 tests; each feature's integration test compares the result with a hand calculation.
• Local. It talks to your running SolidWorks over COM; the server itself makes no network calls.

Quickstart

1. Install uv.

2. Start SolidWorks and leave it open (the server attaches to the running instance — it does not launch one).

3. Register the server with your MCP client.

   Claude Code:

   claude mcp add solidworks -- uvx --from git+https://github.com/hjbaard/SolidWorks-MCP solidworks-mcp
   

   Claude Desktop (claude_desktop_config.json) or any other client:

   {
     "mcpServers": {
       "solidworks": {
         "command": "uvx",
         "args": ["--from", "git+https://github.com/hjbaard/SolidWorks-MCP", "solidworks-mcp"]
       }
     }
   }
   

4. Ask for a part, for example:

   Design a 100 × 80 × 8 mm mounting plate with a Ø16 mm centre bore, four counterbored M5 holes 12 mm from the corners and R5 corners. Check the volume against your own calculation, then export a fine STL.

Requirements and compatibility

• Windows, with SolidWorks installed, licensed and running.
• Python 3.11+ (uv fetches one if needed).
• Tested on SOLIDWORKS 2026 (3DEXPERIENCE R2026x). The API calls it uses exist since SOLIDWORKS 2020 SP2, so 2020–2025 should work, but that is untested. Tried another version? Please open an issue with the result, whether it worked or not.

Status: early (v0.2). It works end-to-end, but tool names and conventions may still change. See CHANGELOG.md.

Troubleshooting

• "Geen draaiende SolidWorks gevonden" / connection fails — SolidWorks must be running before you start the server or run a script; it attaches to the active instance via GetActiveObject and does not launch one.
• First call is slow or EnsureModule errors — the first COM call generates the makepy typelib wrappers under your temp gen_py folder. Let it finish; if it gets into a bad state, delete the gen_py cache and retry. Early binding is mandatory on this build (see Architecture).
• A feature returns {ok: false, error: ...} — that is by design: every tool fails loud with a readable (Dutch) message rather than silently producing wrong geometry. Read the message; it names the likely cause.
• Only tested against SOLIDWORKS 2026 (3DEXPERIENCE R2026x). On other builds the verified enum values or method signatures may differ — re-run scripts/introspect_api.py to inspect your installed typelib.

Development

Clone the repository, then install it editable into a venv:

python -m venv .venv
.\.venv\Scripts\python.exe -m pip install -e .[dev]

To run the MCP server from this checkout instead of via uvx, point your client at the venv's Python:

{
  "mcpServers": {
    "solidworks": {
      "command": "C:\\path\\to\\SolidWorks-MCP\\.venv\\Scripts\\python.exe",
      "args": ["-m", "solidworks_mcp.server"]
    }
  }
}

Run the verification scripts

With SolidWorks open:

.\.venv\Scripts\python.exe scripts\probe_connection.py     # M0
.\.venv\Scripts\python.exe scripts\m1_block.py             # M1
.\.venv\Scripts\python.exe scripts\m2_parametric.py        # M2
.\.venv\Scripts\python.exe scripts\test_mcp_server.py      # M3 (full MCP loop over stdio)
.\.venv\Scripts\python.exe scripts\m5_demo_bracket.py      # M5 (3D-print bracket, every step verified)

scripts/introspect_api.py regenerates/inspects the installed typelib and prints verified enum values — run it if SolidWorks is upgraded and signatures change.

Tests

.\.venv\Scripts\python.exe -m pytest                 # all tests
.\.venv\Scripts\python.exe -m pytest -m "not solidworks"   # fast unit layer, no SolidWorks

Two layers: pure unit tests (units, selector/direction parsing, polygon cleaning, the component-placement maths, and that every MCP tool forwards its arguments to the right session method) run anywhere; integration tests (solidworks marker) drive a running SolidWorks and verify each feature's volume — or each component's placement — against a hand calc. They auto-skip if SolidWorks isn't reachable.

Tools

The server speaks MCP over stdio.

Part tools

Assembly tools

export and screenshot work on assemblies too.

Faces are selected by direction in the component's own frame (+x, -z, …), so a selector keeps meaning the same face however the component is turned. Add :inner (e.g. +y:inner) for the cavity side of a hollow part — the inside of a room wall instead of its outer skin.

All linear dimensions are millimetres; the server converts to/from the SolidWorks-internal metre/radian units at the boundary.

Architecture

src/solidworks_mcp/
  binding.py     early-binding plumbing (wrap raw dispatches in generated classes)
  com_worker.py  one dedicated STA thread; all COM calls serialised through it
  session.py     SolidWorks operations (must run on the COM thread)
  server.py      FastMCP tools that delegate to session via the worker
  constants.py   enum values read from the installed typelib (verified)
  units.py       mm<->m, deg<->rad
  errors.py      SolidWorksError -> agent-facing {ok:false,error}

Two non-obvious design decisions, both load-bearing:

1. Early binding is mandatory. On this build GetActiveObject returns a dispatch whose GetTypeInfo() fails, so EnsureDispatch/CastTo cannot infer types and pure late binding breaks (IModelDoc2.FirstFeature → DISP_E_MEMBERNOTFOUND). We generate makepy wrappers from the installed typelib and wrap each raw dispatch in the right interface class; calls then go by dispid via InvokeTypes, bypassing name resolution. See binding.py.

2. A dedicated COM thread. COM is STA and thread-affine. The MCP server runs on asyncio, so all COM work is pinned to one worker thread (com_worker.py) that handlers post to and await — actively enforcing the "one COM session, single-threaded" rule that does not hold automatically in an async server.

Status and roadmap

Proven end-to-end against SOLIDWORKS 2026 (3DEXPERIENCE R2026x):

See Docs/PROGRESS.md for the detailed log and roadmap. Feedback and contributions are welcome.

Known limitations

• Geometry so far: boxes, cylinders/cones (revolve), arbitrary extruded profiles, holes, polygon pockets/slots (cut_profile), fillets, chamfers, shells, linear + circular patterns (bolt circles); plus equations, materials, geometry inspection, and save/open of .sldprt, holes + pockets on any planar face (model→sketch transform), round flanges (disc + bore + bolt circle), and slotted holes (cut_slot, obround at any angle — the first arc-based sketch), general revolves (add_revolved_profile: any (r,z) profile → shafts, vases, rings), swept pipes/tubes (add_swept_pipe: a round profile along a rounded 2D path), and lofts (add_lofted_solid: blend stacked polygon profiles → transitions/adapters), free-form extrusions (add_extruded_spline: a smooth closed spline → organic/aesthetic outlines), and non-circular sweeps (add_swept_profile: any cross-section along a path → rails, gaskets, trim). Mirror is shelved — both routes fail on this build; an AI mirrors by placing features symmetrically.
• Selection: plane walk, face-by-normal/direction (_planar_face_by_normal, +z/…, with :inner for the cavity side of a hollow part), and edge selection by axis or explicit index (_select_edges). list_faces/list_edges let an agent inspect geometry before selecting.
• Assemblies (M6): components, transforms, mates and interference detection. Component patterns, in-context features, configurations, drawings and Simulation (FEA) are out of scope.