MCP CAD Studio

MCP CAD Studio

A self-contained parametric CAD workspace delivered as an MCP server and an interactive MCP App. Agents can create and edit models through tools; people can work on the same models in a live 3D studio rendered inside any compatible host.

What it does

• Renders a full 3D editor through the studio_ui tool.
• Creates boxes, spheres, cylinders, cones, polygon extrusions, imported meshes, transforms, and nested union/difference/intersection trees.
• Generates editable brackets, pipes, gears, enclosures, and bolts.
• Loads, patches, regenerates, and deletes persistent model documents with optimistic revision checks.
• Preflights extrusion outlines and raw meshes with actionable topology diagnostics before they reach the CAD kernel.
• Imports ASCII/binary STL and OBJ; exports ASCII STL and OBJ.
• Keeps an open app synchronized with model-initiated MCP tool calls.
• Runs over stdio or Streamable HTTP, with direct HTTPS support.
• Uses a bundled WebAssembly CAD kernel—no OpenSCAD, Python, compiler, Docker, or native CAD installation is needed.

The server's data tools are UI-independent. A client that cannot render MCP Apps can still perform every CAD operation and receive structured model/mesh data.

Install

Node.js 20 or later is the only runtime requirement. The CAD engine and all JavaScript dependencies install with the package.

Run the published npm package:

npx -y mcp-cad-studio --stdio

Or clone and build:

git clone https://github.com/flujo-app/mcp-cad-studio.gitcd mcp-cad-studionpm installnpm run buildnpm start -- --stdio

MCP client configuration (stdio)

{  "mcpServers": {    "cad-studio": {      "command": "npx",      "args": ["-y", "mcp-cad-studio", "--stdio"]    }  }}

Models persist by default to ~/.mcp-cad-studio/models.json. Use --data-file <path> to choose another file or --no-persist for an in-memory session.

HTTPS / Streamable HTTP

Run a local HTTPS endpoint with a generated self-signed certificate:

mcp-cad-studio --transport https --host 127.0.0.1 --port 8787

For a remotely reachable production server, use a trusted certificate:

mcp-cad-studio --transport https \  --host 0.0.0.0 \  --port 8787 \  --tls-cert /run/secrets/fullchain.pem \  --tls-key /run/secrets/privkey.pem

The MCP endpoint is /mcp; a read-only health endpoint is available at /health. TLS termination at a reverse proxy is also supported—run with --transport http behind the proxy.

MCP tools

All mutating results include models, activeModel, and mesh in structuredContent, so the UI and model see the same canonical state. Model creation is reserved for genuinely separate models. For revisions, first call load_model, then pass its modelId and revision back as expectedRevision to update_model, generate_model, or delete_model.

Updating without creating copies

update_model preserves the model ID and supports either a complete replacement shape or small RFC 6901 JSON-Pointer-style patches. This changes the X size of a saved box without resending its whole definition:

{  "modelId": "5e44fd24-b7df-450a-a7bb-31c95496832f",  "expectedRevision": 3,  "patches": [    { "op": "replace", "path": "/shape/size/0", "value": 80 }  ]}

Patches can target /shape, /name, or /color and are applied in order. add, replace, and remove are supported. The completed definition is schema-checked and geometry-checked before the saved model is changed.

For template-level edits, such as changing a gear's tooth count, call generate_model with the existing modelId and expectedRevision. The template is regenerated into the same document instead of creating another model.

Parametric model format

create_model and update_model accept a recursive shape tree. For example, a plate with a cylindrical hole:

{  "name": "Mounting plate",  "color": "#60a5fa",  "shape": {    "kind": "difference",    "children": [      { "kind": "box", "size": [80, 50, 6], "center": true },      {        "kind": "cylinder",        "height": 8,        "radius": 5,        "segments": 48,        "center": true      }    ]  }}

Every node can include a transform:

{  "transform": {    "translation": [10, 0, 4],    "rotation": [0, 0, 45],    "scale": [1, 1, 1]  }}

Rotations use degrees. Dimensions are unit-agnostic in the kernel; the studio labels them as millimeters.

Shape objects are strict: misspelled or unsupported fields produce an error instead of being silently ignored. validate_shape checks a draft without saving and reports JSON paths, error codes, and suggested repairs. Checks include:

• repeated, zero-length, zero-area, and self-intersecting extrusion outlines;
• incomplete or out-of-range mesh arrays and degenerate triangles;
• open boundaries, edges shared by too many faces, inconsistent winding, and disconnected surface fans at a vertex;
• shape-tree and twisted-extrusion complexity limits;
• final verification by the Manifold CAD kernel.

If the kernel still rejects a shape, its status is translated into guidance for non-finite vertices, non-manifold geometry, invalid construction, oversized results, and the other kernel status classes.

Architecture

flowchart LR  A[Agent or person] --> H[MCP host]  H <-->|stdio or Streamable HTTP/S| S[MCP CAD Studio server]  H <-->|MCP Apps JSON-RPC bridge| U[Interactive CAD app]  U -->|tools/call| H  S --> P[Persistent parametric documents]  S --> K[Bundled Manifold WebAssembly kernel]  K --> M[Render mesh and STL/OBJ]  M --> S

The studio_ui tool links to ui://cad-studio/studio.html with _meta.ui.resourceUri. The component uses the stable MCP Apps bridge (ui/initialize, ui/notifications/*, and tools/call) rather than requiring host-specific globals. Model polling is revision-aware, making external tool edits visible in an already-open editor.

Development

npm installnpm run check

npm run check performs strict TypeScript checking, 16 kernel/store/protocol/ transport tests, and a production build. The test suite uses the real WebAssembly geometry engine and both in-memory and Streamable HTTP MCP clients.

Useful commands:

npm run dev       # HTTP development server on port 8787npm test          # Vitest suitenpm run typecheck # TypeScript onlynpm run build     # bundle the MCP App and servernpm pack          # verify the single-package artifact

To publish the current version to npm:

npm run release

The release command signs in through npm when necessary, runs the complete check suite, publishes the package publicly, and confirms that npm serves the version. It is safe to rerun: if that exact version is already published, it verifies the project and skips the duplicate publish.

Run npm run release:check to validate the release helper without publishing.

Security notes

• Tool schemas cap shape depth, node count, mesh size, and imported file size.
• Mutation tools accurately declare read-only/destructive/open-world hints.
• expectedRevision prevents accidental overwrites and stale deletion during concurrent editing.
• Patch paths are restricted to editable model fields and reject prototype traversal.
• The app resource declares an empty external-resource/connect CSP.
• A generated self-signed certificate is intended for local development only.
• Authentication is deployment-specific. Put remote multi-user instances behind an authenticated gateway and enforce per-user authorization there.

License

MIT