fluidcad-custom-features

Provenance: maintained in the FluidCAD repo (https://github.com/Fluid-CAD/FluidCAD), under mcp/skills/. The installed local skill files are the runtime source of truth.

Writing a custom feature

This skill layers on top of the fluidcad skill. That one owns the loop: read the docs, plan in generic CAD terms, build in increments, check render.state and objectErrors, resolve filters before writing them, screenshot when a feature earns it, and report only what was checked. Follow it for the test part. This skill covers what is specific to a custom feature: deciding that one is warranted, designing it as a feature a user fills in, writing the module, and proving it in a part.

The governing principle: a custom feature is a CAD feature first and code second. Its user picks a face and types a height in a dialog, then fillets its rim and repeats it; design for that user, write the code to that design, and prove it the way that user will use it.

1. Decide whether one is warranted

Write a custom feature when one construction recurs (across models, or across places in a model with different values) and should be one statement, one dialog, one timeline row: a PCB standoff on any face, a ring of clearance holes around any axis, a vent grid on any panel, bosses at a set of connectors.

Don't write one, and say why, when:

• the geometry occurs once: write the statements in the model;
• it is the same geometry again in one model: repeat() re-applies a feature at new positions, copy() duplicates a finished shape;
• it is a whole part reused with other dimensions: a part() with param() values, inserted where needed (the fluidcad-assembly skill) — unless one feature builds that part and it should carry the feature's dialog: then the feature plus definePart (section 9);
• it is several parts that move against each other, sized from one set of values (a wardrobe with hinged doors and sliding drawers): a generated assembly, Generator + defineAssembly (section 9);
• a built-in already does it (hole() for drilled, clearance, tapped, counterbored and countersunk holes; draft(); rib(); shell()): search the docs first.