Text To Cad

Generate validated parametric CAD parts from text or drawings.

Skill metadata

Source	Bundled (installed by default)
Path	skills/creative/text-to-cad
Version	1.0.0
Author	Fabric
License	MIT
Platforms	linux, macos, windows
Tags	cad, build123d, step, stl, 3d-printing, parametric, hardware
Related skills	hardware-manufacturing

Reference: full SKILL.md

info

The following is the complete skill definition that Fabric loads when this skill is triggered. This is what the agent sees as instructions when the skill is active.

Text-to-CAD

Overview

Turn a natural-language description (optionally with reference images or 2D drawings) into a parametric CAD part. You write a small build123d Python generator, run it in the skill's isolated environment, validate the geometry numerically, and deliver STEP as the primary artifact with STL/3MF/GLB as secondary exports plus PNG snapshots for visual review. The .py generator is the model: it is source-controlled, parameter-editable, and regenerating it reproduces every artifact byte-for-byte deterministically.

Code-first modeling (build123d on the OpenCASCADE kernel) is the default because it is deterministic and reviewable. A cloud fallback (scripts/zoo_text_to_cad.py, Zoo Text-to-CAD API) exists for organic or underspecified shapes where parametric code is not converging — see references/providers.md for the landscape and trade-offs.

When to Use

• "Design/model/CAD me a <part>" — brackets, enclosures, plates, adapters, spacers, mounts, gears, jigs, fixtures
• Producing STEP/STL/3MF/GLB files for machining, 3D printing, or import into Fusion 360 / FreeCAD / Onshape
• Modifying a part this skill generated earlier (edit the generator, rerun)
• Measuring or sanity-checking an existing STEP/STL file (scripts/cadcheck.py)

Don't use for: photorealistic renders or concept art (image generation), animated 3D scenes (manim-video), architectural BIM, CAM toolpaths, or manufacturing strategy beyond the part itself (hardware-manufacturing).

Modeling Defaults

State any deviation explicitly in the brief; otherwise these hold:

Convention	Default
Units	millimeters, everywhere
Base plane / up axis	XY plane, +Z up
Solids	closed, positive volume
Enclosure walls	2.0–3.0 mm
M3 / M4 / M5 clearance holes	3.4 / 4.5 / 5.5 mm
Cosmetic fillets	1.0–3.0 mm where geometrically safe

Environment (isolated — never core dependencies)

CAD libraries are heavyweight and must not enter pyproject.toml or uv.lock. The skill owns a private virtualenv:

python scripts/setup.py       # works on macOS, Linux, and Windows
# Unix convenience wrapper:
bash scripts/setup.sh

setup.py installs the pinned requirements.txt (build123d, numpy-stl, matplotlib, ezdxf) with uv when available, else pip. It chooses the platform's venv interpreter (bin/python or Scripts/python.exe) and prints that path on success — use it for every script below. Done when setup exits 0 and prints the interpreter path.

Pipeline

BRIEF --> SETUP --> MODEL --> CHECK --> EXPORT --> SNAPSHOT --> REVIEW

1. BRIEF — Extract every dimension, unit, datum, and validation target from the request into a short written brief (see references/cad-brief.md for prose/image/drawing extraction). Done when: every dimension has a number + unit, or a named assumption from the defaults table.
2. SETUP — Run python scripts/setup.py (or scripts/setup.sh on Unix). Done when: it prints the venv python.
3. MODEL — Write <part>.py next to where the outputs belong, parameters as named constants at the top, exports sharing the generator's basename (bracket.py → bracket.step). Patterns, selectors, and error fixes: references/build123d-modeling.md. Never edit generated artifacts by hand; edit the generator. Done when: the generator runs clean under the venv python and writes its exports.
4. CHECK — <venv-python> scripts/cadcheck.py <part>.step --expect-bbox X,Y,Z --min-volume V prints JSON geometry facts (solids, volume, area, bounding box, validity) and exits non-zero on failure. Done when: facts match the brief's targets within tolerance.
5. EXPORT — STEP is mandatory; add STL/3MF/GLB per the request (references/validation-and-exports.md). Done when: every requested format exists on disk.
6. SNAPSHOT — <venv-python> scripts/cadsnap.py <part>.step -o <part>.png renders iso/front/top/right views. Review the PNG against the brief. Done when: the snapshot visually matches the brief (hole count, proportions, features present).
7. REVIEW / ITERATE — On any mismatch, change the smallest responsible parameter or feature in the generator and rerun steps 3–6. Done when: the final response lists artifact paths, the cadcheck facts that were actually verified, the snapshot, and every assumption made.

Scripts

Script	Purpose	Reference
scripts/setup.py	Cross-platform preflight + isolated venv setup	—
scripts/setup.sh	Unix wrapper for setup.py	—
scripts/cadcheck.py	Geometry facts + pass/fail validation for STEP/STL	validation-and-exports.md
scripts/cadsnap.py	Multi-view PNG snapshots from STEP/STL	validation-and-exports.md
scripts/stdparts.py	Parametric ISO fasteners (screws, nuts, washers)	standard-parts.md
scripts/assembly.py	Combine placed STEP parts, flag bbox overlap	assemblies.md
scripts/printcheck.py	FDM print-readiness checks from an STL	print-prep.md
scripts/dxfcheck.py	Validate 2D DXF cut profiles (closure, extents)	dxf-drawings.md
scripts/cadviewer.py	Self-contained HTML 3D viewer from a GLB	validation-and-exports.md
scripts/zoo_text_to_cad.py	Cloud generation via the Zoo Text-to-CAD API	providers.md

Stack Capabilities

Beyond single-part generation, the skill covers the surrounding hardware workflow. Reach for these when the request needs them; each has its own reference and, where it produces a file, its own validator.

• Standard parts — don't model a screw from scratch. stdparts.py emits sized ISO fasteners as STEP so mating features clear real hardware.
• Assemblies — place parts by explicit transform and export one STEP; assembly.py reports bounding-box interference (use --allow-overlap for intended fits like screws in bores).
• 2D DXF drawings — author flat cut profiles with build123d's ExportDXF; validate closure and extents with dxfcheck.py before sending to a laser cutter.
• Print prep — printcheck.py verifies an STL fits the bed and flags steep overhangs and thin features before slicing (no slicer required).
• Interactive viewer — cadviewer.py wraps a GLB into a portable, shareable single-file HTML viewer (orbit/zoom) for review or handoff.

Cloud Fallback: Zoo Text-to-CAD

For organic shapes or when parametric code is not converging after ~3 iterations, offer the Zoo ML API (requires the ZOO_API_TOKEN environment variable; the user creates a token at zoo.dev):

<venv-python> scripts/zoo_text_to_cad.py "a 40mm herringbone gear" --format step --out gear.step

Cloud output is a mesh-derived artifact, not a parameter-editable generator — say so when delivering it, and still run CHECK and SNAPSHOT on the result.

Common Pitfalls

1. Part.is_valid is a property, not a method in current build123d — part.is_valid() raises TypeError: 'bool' object is not callable.
2. Editing exported STEP/STL by hand. The generator is the source of truth; regenerate instead, or the next rerun silently reverts your edit.
3. Installing CAD deps into the repo or system python. They belong only in the skill venv; uv.lock/pyproject.toml changes are a shared-surface violation and will be rejected.
4. Delivering STL without STEP. Meshes are lossy; STEP is the primary, editable interchange artifact. Export both.
5. Unit drift. build123d is unitless — the mm convention only holds if every literal is mm. Convert inches/cm in the brief, not in the code.
6. Trusting the picture. A snapshot that "looks right" can hide a non-manifold solid or an off-by-2x scale. cadcheck facts are the gate; the snapshot is corroboration.
7. Subtracting holes after fillets. Order features so fillets come last; filleting edges consumed by a later boolean fails or produces slivers.

Verification Checklist

• Brief written; every dimension numbered or explicitly assumed
• Generator <part>.py runs clean in the skill venv
• cadcheck.py passed: closed solid, positive volume, bbox within brief
• STEP exported; requested secondary formats (STL/3MF/GLB) exported
• Snapshot PNG rendered and reviewed against the brief
• Final response lists artifact paths, verified facts, and assumptions
• No changes to pyproject.toml, uv.lock, or the system python