FastBuild123

Turn any build123d model into a live, interactive parametric web UI. Annotate your part function's parameters with a FastAPI-style @app.part() decorator and get auto-generated sliders in the browser with instant 3D preview — the type-annotated signature is the UI definition.

Quick start

Run a bundled example without installing anything:

uvx fastbuild123 demo enclosure

Or install it into your own project:

uv add fastbuild123      # or: pip install fastbuild123
fastbuild view my_model.py

A browser page opens with parameter controls on the left and a live 3D view on the right. Drag a slider or save the file — the model updates in place, keeping your camera pose, tree state, and clipping planes. A model that raises keeps the last-good geometry on screen with an error banner; fix the file and it recovers.

Defining parts

from typing import Annotated, Literal
from build123d import Part, Box
from fastbuild import App, Group, Range

app = App()

@app.part()
def enclosure(
    width:  Annotated[float, Range(20, 200, step=1, unit="mm")] = 80,
    wall:   Annotated[float, Range(0.8, 5, step=0.1, unit="mm")] = 2,
    ribs:   Annotated[int, Range(0, 8), Group("Ribs")] = 4,
    vented: bool = False,
    style:  Literal["rounded", "chamfered"] = "rounded",
) -> Part:
    ...

Widget mapping: float/int + Range → slider, bare numbers → number input, bool → checkbox, Literal/Enum → dropdown. Every parameter needs a default — defaults are the initial build. Multiple @app.part() functions in one file get a part selector. Add Group("Label") to a parameter's annotation to place it under a named collapsible section in the panel; ungrouped parameters render first.

Headless export

fastbuild export my_model.py enclosure --param width=120 -o enclosure.step

Values are validated against each parameter's Range; output format follows the extension (.step/.stp/.stl).

Requirements

Python 3.10–3.13 on macOS (Apple Silicon or Intel), Linux (glibc 2.31+, x86-64 or aarch64), or 64-bit Windows — wherever cadquery-ocp publishes wheels. Expect a ~500 MB install; the OpenCASCADE kernel is most of it. Alpine/musl is not supported.

Development

uv sync
uv run pytest
uv run fastbuild demo enclosure

Examples live in fastbuild/examples/ so they ship with the package and stay runnable via fastbuild demo. Specs live in specs/. The 3D component is a vendored, pinned build of three-cad-viewer (fastbuild/static/vendor/, see VERSION there) fed by ocp-tessellate output over a versioned websocket protocol.

License

MIT — see LICENSE. Bundles three-cad-viewer (MIT), whose license is included at fastbuild/static/vendor/LICENSE-three-cad-viewer.