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), an M10 bolt with a real thread, a revolved + shelled vase, a swept pipe, a lofted + shelled horn.}

Why this server

• It verifies, not just generates. Features report measured geometry;
  dimensions and mates are measured back after the rebuild.
• Fully defined sketches. Every sketch is constrained the way a designer
  would: dimensions from the origin, relations only where the geometry is
  exactly horizontal, vertical or on the origin. Tools return their dimensions
  by role (width@Sketch1), so the part stays editable, in SolidWorks or
  through the agent.
• Real CAD, not just primitives. Extrude, revolve, sweep, loft and splines;
  holes, counterbores, slots and pockets on any face; rounded polygon corners; ISO holes from the Hole Wizard; real ISO metric threads;
  fillets, chamfers, shells, patterns, mirrors, ribs, equations and materials. Assemblies
  with mates and interference checks. STEP/STL/3MF export and screenshots.
  Engraved and embossed text. Work on existing parts: list, delete, suppress and reorder features; read, extrude and cut a person's sketches; import STEP. Joints with concentric and angle mates, checked over their range. Printability checks and dimensioned drawings. Planes at any offset or angle. Several bodies per part, combined and split. Variable fillets and full rounds. Free sketches with tangent arcs and splines. 85 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. 673 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 solidworks-mcp
   

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

   {
     "mcpServers": {
       "solidworks": {
         "command": "uvx",
         "args": ["solidworks-mcp"]
       }
     }
   }
   

   It is also listed in the official
   MCP Registry
   as io.github.hjbaard/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.

Guidelines for agents

The server hands every MCP client short modelling guidelines when it connects
(conventions, verify each step, known pitfalls). The full guide is the resource
solidworks://guide: recipes for holes, ribs, threads and assemblies, 3D-print
advice, and how to reverse-engineer a part from a mesh (STL/3MF). The same text
is in src/solidworks_mcp/guide.md.

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. To check your installation, run this with SolidWorks open:

  uvx solidworks-mcp --selftest
  

  It builds a few small parts, compares each with a hand calculation and
  closes them unsaved. Please paste its output in a
  compatibility report,
  whether it worked or not.

Status: early (0.x). It works end-to-end, but tool names and conventions
may still change. See CHANGELOG.md.

Troubleshooting

• Start with the selftest: uvx solidworks-mcp --selftest shows your
  SolidWorks release, language and templates, and which tool areas work. Add
  its output to a bug report.
• "No running SolidWorks found" / 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 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), and mirrors (add_mirror: features or the whole
  body about a plane through the part).
• 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.