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MCP OpenSCAD Render Loop

OpenSCAD wrapped as an MCP server so an agent can iterate on parametric CAD designs without bouncing in and out of the GUI. Render .scad source with parameter overrides, run parameter sweeps, validate syntax, extract module signatures, and compute STL geometry metrics.

Tools

• render_stl — render a .scad file or inline source to STL with -D parameter overrides

• render_png — preview render to PNG with camera + image-size control

• parametric_sweep — Cartesian sweep over one or more parameter ranges, returns a manifest of outputs

• validate_scad — syntax check via openscad --check (no render)

• list_modules — extract top-level module foo(...) and function bar(...) signatures with defaults

• compute_metrics — bounding box, volume, surface area, triangle count from an STL

Why this server exists

OpenSCAD's CLI is well-designed but verbose. Most agent CAD workflows do the same loop: edit parameters → render → measure → adjust. This server collapses that to one tool call per iteration and returns geometry metrics directly so the agent doesn't have to parse STL bytes itself.

Quick start

# 1. Install OpenSCAD (must be on PATH)
brew install openscad      # macOS
apt-get install openscad   # Debian/Ubuntu

# 2. Install the MCP server
pip install mcp-openscad-render-loop

# 3. Set output directory and run
export MCP_OPENSCAD_OUTPUT_DIR="/tmp/scad-renders"
mcp-openscad-render-loop serve

Claude Desktop config:

{
  "mcpServers": {
    "openscad": {
      "command": "mcp-openscad-render-loop",
      "args": ["serve"],
      "env": {
        "MCP_OPENSCAD_OUTPUT_DIR": "/tmp/scad-renders",
        "MCP_OPENSCAD_BINARY": "/usr/local/bin/openscad"
      }
    }
  }
}

Typical agent workflow

Agent: "Design an enclosure for a 60x40x15mm PCB with 2mm walls and M3 mounting posts."
↓
1. list_modules on enclosure.scad → finds module enclosure(pcb_l, pcb_w, pcb_h, wall, post_dia)
2. render_stl with pcb_l=60, pcb_w=40, pcb_h=15, wall=2, post_dia=3 → enclosure_v1.stl
3. compute_metrics on enclosure_v1.stl → bbox 66x46x21, volume 18.4cm³, 1,240 triangles
4. parametric_sweep on wall ∈ [1.5, 2.0, 2.5] → 3 STLs + metrics → wall=2 is the strength/weight knee
5. render_png at iso camera → preview image attached to agent's reply

Safety

• MCP_OPENSCAD_OUTPUT_DIR is the only writable path. Any output path outside this dir is rejected.

• Each render is hard-capped at 60 seconds (configurable). Long sweeps run renders sequentially, not in parallel — keeps memory bounded.

• Inline .scad source is written to a temp file inside the output dir; nothing executes outside openscad.

• No import("/some/path.dxf") traversal — relative paths in .scad are resolved against the output dir or the source file's dir, never against /.

License

MIT.