vcad - SKILL.md Agent Skill

name: vcad description: Create 3D CAD models using vcad MCP tools. Use when the user asks to create 3D parts, mechanical components, enclosures, brackets, gears, or any parametric geometry. Supports primitives, sketch-based operations (extrude, revolve, sweep, loft), booleans, patterns, fillets, shell, assemblies, and export to STL/GLB.

vcad - Parametric CAD for AI Agents

Create 3D CAD models programmatically using the vcad MCP tools. All dimensions are in millimeters.

Available Tools

Tool	Purpose
`create_cad_document`	Build geometry from primitives, sketches, and operations
`export_cad`	Export to STL (3D printing) or GLB (visualization)
`inspect_cad`	Get volume, surface area, bounding box, center of mass, mass
`import_step`	Import geometry from STEP files
`open_in_browser`	Generate shareable vcad.io URL
`get_changelog`	Query recent changes and features

For assembly and physics tools, see the assembly-physics skill.

Output Format

Use "format": "vcode" (default) for token-efficient output (~5x smaller). Use "format": "json" for human-readable debugging.

Part Types

Each part must use exactly ONE base geometry type:

Primitive-based

{
  "name": "plate",
  "primitive": {"type": "cube", "size": {"x": 100, "y": 60, "z": 5}},
  "operations": [...]
}

Extrude-based (sketch → solid)

{
  "name": "bracket",
  "extrude": {
    "sketch": {
      "plane": "xy",
      "shape": {"type": "rectangle", "width": 40, "height": 20, "centered": true}
    },
    "height": 10
  }
}

Revolve-based (sketch → solid of revolution)

{
  "name": "vase",
  "revolve": {
    "sketch": {
      "plane": "xy",
      "shape": {
        "type": "polygon",
        "points": [
          {"x": 10, "y": 0}, {"x": 15, "y": 20},
          {"x": 12, "y": 40}, {"x": 14, "y": 50},
          {"x": 0, "y": 50}, {"x": 0, "y": 0}
        ]
      }
    },
    "axis": "y",
    "angle_deg": 360
  }
}

Sweep-based (sketch along path)

{
  "name": "tube",
  "sweep": {
    "sketch": {
      "shape": {"type": "circle", "radius": 5}
    },
    "path": {"type": "line", "start": {"x": 0, "y": 0, "z": 0}, "end": {"x": 50, "y": 0, "z": 30}}
  }
}

Helix path for springs/threads:

"path": {"type": "helix", "radius": 20, "pitch": 10, "height": 60}

Optional sweep parameters: twist_deg, scale_start, scale_end.

Loft-based (interpolate between sketches)

{
  "name": "transition",
  "loft": {
    "sketches": [
      {"plane": "xy", "at": {"x": 0, "y": 0, "z": 0}, "shape": {"type": "rectangle", "width": 40, "height": 40, "centered": true}},
      {"plane": "xy", "at": {"x": 0, "y": 0, "z": 30}, "shape": {"type": "circle", "radius": 15}}
    ]
  }
}

Sketch Shapes

Sketches are used by extrude, revolve, sweep, and loft operations:

Shape	Parameters
`rectangle`	`width`, `height`, `centered` (bool, default false)
`circle`	`radius`
`polygon`	`points` (array of `{x, y}`), `closed` (default true)

Sketch planes: "xy" (default), "xz", "yz". Origin set with "at": {x, y, z}.

Primitive Origins

Primitive	Origin	Extent
Cube	Corner at (0,0,0)	Extends to (size.x, size.y, size.z)
Cylinder	Base center at (0,0,0)	Height along +Z
Sphere	Center at (0,0,0)	Radius in all directions
Cone	Base center at (0,0,0)	Height along +Z, `radius_bottom`/`radius_top`

Positioning

The at parameter for boolean operations and holes:

Absolute: {"x": 25, "y": 15, "z": 0} — exact coordinates in mm
Named: "center", "top-center", "bottom-center" — relative to base primitive
Percentage: {"x": "50%", "y": "50%"} — percentage of base primitive bounds

Operations

Applied in order after the base geometry:

Operation	Key Parameters
`union`	`primitive`, `at`
`difference`	`primitive`, `at`
`intersection`	`primitive`, `at`
`hole`	`diameter`, `at`, `depth` (omit for through-hole)
`translate`	`offset: {x, y, z}`
`rotate`	`angles: {x, y, z}` (degrees)
`scale`	`factor: {x, y, z}`
`linear_pattern`	`direction: {x, y, z}`, `count`, `spacing`
`circular_pattern`	`axis_origin`, `axis_dir`, `count`, `angle_deg`
`fillet`	`radius` — rounds all edges
`chamfer`	`distance` — bevels all edges
`shell`	`thickness` — hollows the part

Materials

Assign via "material" on each part: "steel" (density 7850), "aluminum" (2700), "default".

inspect_cad reports mass when density is available.

Common Patterns

Plate with Corner Holes

{
  "parts": [{
    "name": "mounting_plate",
    "primitive": {"type": "cube", "size": {"x": 100, "y": 60, "z": 5}},
    "operations": [
      {"type": "hole", "diameter": 4, "at": {"x": 10, "y": 10}},
      {"type": "hole", "diameter": 4, "at": {"x": 90, "y": 10}},
      {"type": "hole", "diameter": 4, "at": {"x": 10, "y": 50}},
      {"type": "hole", "diameter": 4, "at": {"x": 90, "y": 50}}
    ]
  }]
}

Cylinder with Blind Hole

{
  "parts": [{
    "name": "bushing",
    "primitive": {"type": "cylinder", "radius": 15, "height": 20},
    "operations": [
      {"type": "hole", "diameter": 10, "depth": 15, "at": "center"}
    ]
  }]
}

L-Bracket

{
  "parts": [{
    "name": "bracket",
    "primitive": {"type": "cube", "size": {"x": 40, "y": 40, "z": 5}},
    "operations": [
      {"type": "union", "primitive": {"type": "cube", "size": {"x": 5, "y": 40, "z": 30}}, "at": {"x": 0, "y": 0, "z": 5}},
      {"type": "hole", "diameter": 5, "at": {"x": 20, "y": 20}},
      {"type": "difference", "primitive": {"type": "cylinder", "radius": 2.5, "height": 40}, "at": {"x": 2.5, "y": 20, "z": 20}}
    ]
  }]
}

Flange with Circular Bolt Pattern

{
  "parts": [{
    "name": "flange",
    "primitive": {"type": "cylinder", "radius": 40, "height": 10},
    "operations": [
      {"type": "hole", "diameter": 20, "at": "center"},
      {"type": "difference", "primitive": {"type": "cylinder", "radius": 4, "height": 15}, "at": {"x": 30, "y": 0, "z": -2}},
      {"type": "circular_pattern", "axis_origin": {"x": 0, "y": 0, "z": 0}, "axis_dir": {"x": 0, "y": 0, "z": 1}, "count": 6, "angle_deg": 360}
    ]
  }]
}

Linear Pattern of Holes

{
  "parts": [{
    "name": "rail",
    "primitive": {"type": "cube", "size": {"x": 200, "y": 20, "z": 10}},
    "operations": [
      {"type": "difference", "primitive": {"type": "cylinder", "radius": 3, "height": 15}, "at": {"x": 20, "y": 10, "z": -2}},
      {"type": "linear_pattern", "direction": {"x": 1, "y": 0, "z": 0}, "count": 5, "spacing": 40}
    ]
  }]
}

Extruded T-Profile

{
  "parts": [{
    "name": "t_beam",
    "extrude": {
      "sketch": {
        "plane": "xz",
        "shape": {
          "type": "polygon",
          "points": [
            {"x": -25, "y": 0}, {"x": 25, "y": 0},
            {"x": 25, "y": 3}, {"x": 3, "y": 3},
            {"x": 3, "y": 30}, {"x": -3, "y": 30},
            {"x": -3, "y": 3}, {"x": -25, "y": 3}
          ]
        }
      },
      "height": 100
    }
  }]
}

Shelled Box (Enclosure)

{
  "parts": [{
    "name": "enclosure",
    "primitive": {"type": "cube", "size": {"x": 80, "y": 60, "z": 40}},
    "operations": [
      {"type": "shell", "thickness": 2}
    ]
  }]
}

Filleted Part

{
  "parts": [{
    "name": "rounded_block",
    "primitive": {"type": "cube", "size": {"x": 30, "y": 20, "z": 15}},
    "operations": [
      {"type": "fillet", "radius": 2}
    ]
  }]
}

Spring (Helix Sweep)

{
  "parts": [{
    "name": "spring",
    "sweep": {
      "sketch": {"shape": {"type": "circle", "radius": 1.5}},
      "path": {"type": "helix", "radius": 10, "pitch": 8, "height": 40}
    },
    "material": "steel"
  }]
}

Workflow

Create — create_cad_document to build geometry
Inspect — inspect_cad to verify dimensions, volume, and mass
Export — export_cad to save as .stl or .glb
Share — open_in_browser to generate a vcad.io URL

Tips

Holes default to through-holes; specify depth for blind holes
Use percentage positioning for parametric designs that scale
Cube origin is at corner — add half-size to center operations
Cylinder/cone origins are at base center — no X/Y offset needed for centered holes
Always extend cutting cylinders past the part (the hole operation does this automatically)
fillet and chamfer apply to all edges — use them as the last operation
shell hollows the entire part — combine with difference to remove specific faces
For multi-part designs, define each part in the parts array with a unique name
Use "format": "vcode" (default) to save tokens in the response