# Backend capabilities

## build123d through CAD Skill

Use as the default STEP-first backend.

Best fit:

- Brackets, connecting rods, cranks, levers, shafts, bushings, flanges, plates, housings, covers, enclosures, fixtures, and machined features.
- Parametric Python sources with holes, pockets, slots, bosses, ribs, shells, fillets, chamfers, lofts, sweeps, and revolves.
- Source-level assemblies, named datums, joints, imported components, measurements, alignment checks, and existing STEP inspection.
- STEP primary output with STL, 3MF, or GLB sidecars.

Weak signals: a specialized mechanical family already implemented by SimpleCADAPI, SCAD-native output, browser-only execution, or decorative repeated CSG where OpenSCAD is substantially shorter.

## SimpleCADAPI

Use for its standard mechanical factories and replayable modeling graph.

Best fit:

- Spur, helical, and herringbone gears; internal ring gears; racks; cycloidal discs; ball bearings.
- Planetary and cycloidal reducers, joint actuators, and mechanism-heavy assemblies.
- Parameter expressions, operation-graph JSON, replay, semantic tags, topology queries, and FreeCAD translation.
- Reusable mechanical product families whose formulas should become deterministic library functions.

Before invocation, inspect the installed package and Skill versions together. Do not mix the current single-`Solid` boolean API with older `*rsolidlist` documentation. If the installed runtime and docs disagree, stop that route and use build123d or repair the installation.

## CADAM

Use CADAM's separately installed OpenSCAD WASM runtime for fast CSG authoring and printable parameterized models. Execute generated SCAD through `scripts/cadam_compile.mjs`; do not copy CADAM's GPL runtime into this Skill.

Best fit:

- Vases, containers, knobs, adapters, printable threads, lattice/honeycomb patterns, repeated details, decorative models, and quick concept geometry.
- SCAD source, STL output, simple projected DXF, and UI-facing parameter controls.
- BOSL/BOSL2/MCAD-backed printable features.

Do not use as the primary route for editable STEP, stable face/edge references, fit-critical source-level assemblies, or modification of imported STEP.

## Router refinement and repair

Use text-to-cad's own requirement expansion and visual repair when requirements
are vague, reference images carry important intent, or visual complexity makes
one-pass generation unreliable:

1. Refine the request into a measurable brief.
2. Confirm important fit- or safety-critical unknowns.
3. Generate and execute backend source.
4. Validate deterministic geometry facts.
5. Inspect a multi-view render against the brief.
6. Repair visual mismatches, capped at three automatic visual rounds.

## Focused downstream Skills

- `$dxf`: 2D profiles, flat patterns, laser/plasma/waterjet drawings.
- `$urdf`, `$srdf`, `$sdf`: robot structure, MoveIt semantics, and simulation models/worlds.
- `$gcode`: slice validated meshes with a real slicer.
- `$sendcutsend`: vendor-specific manufacturing preflight.
- `$bambu-labs`: cautious local printer handoff.
- `$cad-viewer`: visual review of supported generated artifacts.