# ParCAD: open source CAD MCP server for Claude, ChatGPT and Cursor > Open source CAD your AI drives over MCP. Add mcp.parcad.dev/mcp to Claude, ChatGPT or Cursor, or run it on your own machine. Parts are JavaScript on an OpenCASCADE kernel, measured and checked, and exported as STEP, 3MF or STL for 3D printing. Experimental, made by Maging Studio. Units are millimetres. AGPL-3.0 or later; the parts you make are yours. Source: https://github.com/ierehon1905/parcad ## Get it - Your AI · nothing to install: `https://mcp.parcad.dev/mcp` - macOS · Linux: `brew tap ierehon1905/parcad && brew install parcad` - Desktop app · Windows, macOS, Linux: [Download from Releases](https://github.com/ierehon1905/parcad/releases) - Browser · nothing to install: [Open ParCAD web](https://parcad.dev/app/) ## Connect your AI The hosted MCP server is https://mcp.parcad.dev/mcp. Sign in with GitHub or Google when your client asks. - Claude (web and desktop): Customize, then Connectors, then Add custom connector. Paste the URL and sign in with GitHub or Google. - Claude Code: One line, then sign in when /mcp asks. ```bash claude mcp add --transport http parcad https://mcp.parcad.dev/mcp ``` - Codex: Add it, then sign in. ```bash codex mcp add parcad --url https://mcp.parcad.dev/mcp && codex mcp login parcad ``` - ChatGPT, Cursor and other clients: Add a remote MCP server with the URL. The client opens the sign-in page itself. ## The case for it ### Select edges by description Write what you mean: the circular rims that open onto the top face, the seam where the arm meets the hub. The description keeps matching after you move a hole or add three more. ### A drifted selector stops the build Add .expect({ count: 4 }) to a selector. If an edit changes what it matches, the build stops and lists every edge it found, with its length and position, so you know what to change. ```text expected 3 edge(s), but matched 4. The model's topology changed; inspect the current edges and update the selector or expectation. The edges matched, shortest first: 18.84 mm arc at (-18.00, -20.00, 4.00), convex 90° 18.84 mm arc at (-18.00, 20.00, 4.00), convex 90° 18.84 mm arc at (18.00, -20.00, 4.00), convex 90° 18.84 mm arc at (18.00, 20.00, 4.00), convex 90° ``` ### One OpenCASCADE model Your script builds a small graph, and OpenCASCADE turns it into faces and edges. The viewport, the measurements and the STEP file all come from that one solid. ### Every number is measured Reports read volume, wall thickness, whether two bores meet and the gap between a lid and its base off the built solid. The jar and cap in the picture sit 0.25 mm apart on the thread. ### See inside the part Cut any part on a plane to check that bores meet and walls keep their thickness. An agent gets the same section views over MCP. ## In code ### Selectors `bracket.js`: ```js const plate = box(80, 60, 8).tag("plate"); const wall = box(8, 60, 40).at(-36, 0, 20).tag("wall"); const body = union(plate, wall, { blend: 6 }); // the blend is the fillet const drilled = body.cut( ...grid(2, 2, 36, 40).map(([x, y]) => cylinder(3, 32).at(x, y)), ); return drilled .edges({ curve: "circle", role: "hole", adjacentTo: { faceNormal: "+z" }, }) .expect({ count: 4 }) // four rims, or the build stops .fillet(0.8); ``` - Size: 80 × 60 × 44 mm - Volume: 55 231.168 mm³ - Bodies: 1 - Watertight: yes The selector matches the four hole rims on the top face. Move a hole and it matches them again; lose one and the build stops at .expect(). ### Two bodies `spur-gears.js`: ```js const m = 2; const pinionTeeth = 20; const wheelTeeth = 30; const width = 8; const backlash = 0.1; const centres = (m * (pinionTeeth + wheelTeeth)) / 2; const pinion = extrude( spurGearOutline({ module: m, teeth: pinionTeeth, backlash }), width, ) .cut(cylinder(5 / 2, width * 2)) .tag("pinion"); const wheel = extrude( spurGearOutline({ module: m, teeth: wheelTeeth, backlash }), width, ) .cut(cylinder(8 / 2, width * 2)) .rotate("z", 180 / wheelTeeth) .at(centres, 0, 0) .tag("wheel"); return { pinion, wheel }; ``` - Pinion ↔ wheel: clear - Clearance: 0.094 mm - Bodies: 2 - Volume: 31 375.868 mm³ 0.1 mm of backlash predicts 0.1 · cos 20° = 0.094 mm between the flanks. The kernel measures 0.094 mm. ### Sections `tools/call · evaluate_part`: ```json { "name": "evaluate_part", "arguments": { "script": "…examples/manifold-block.js…", "views": ["iso"], "section": { "axis": "y" } } } ``` - Size: 80 × 50 × 40 mm - Volume: 145 263.889 mm³ - Cut: y, through the middle - Watertight: yes Cut the block on a plane to check that the drilled galleries meet. The cut applies to the picture only. ### Tags `bracket.js`: ```js const plate = box(w, d, t).tag("plate"); const wall = box(t, d, wallH) .at(-(w - t) / 2, 0, (wallH + t) / 2 - t / 2) .tag("wall"); const drilled = body .cut(...grid(2, 2, 36, 40).map(([x, y]) => hole.at(x, y))) .tag("mount_holes"); return chamferedBase .vertices(">X and >Y and