# build123d

53 Hacker News commenters recommended build123d and 9 criticized it, November 2025 to November 2026. It was recommended in 11 of 13 months; owners who said how long report a median of 1 years (3 owners). It meets the Hacker Approved badge rule.

**Verdict:** Python CAD library that builds solid models and exports STEP files, liked for its Python-friendly design and AI coding assistant use. Common caveat: documentation is often lacking.

## Why people recommend it

- Works well with AI coding assistants (6 comments): "I've had a positive experience building a library of parametric HVAC duct parts using Claude, Gemini and Codex" ([source](https://news.ycombinator.com/item?id=48237448)) "I have been using these models to make 3d models with build123d — they are great at it." ([source](https://news.ycombinator.com/item?id=50001543)) "I model with `build123d` or `openscad` using Claude Code to do the heavy lifting" ([source](https://news.ycombinator.com/item?id=50158907))
- Exports STEP files (5 comments): "I like build123d simply because it can export proper STEP (like CadQuery) but has a nicely python friendly design." ([source](https://news.ycombinator.com/item?id=49677974)) "at least build123d (which I had never heard of, thanks!) can export STEP" ([source](https://news.ycombinator.com/item?id=46031868)) "you can use CadQuery/Build123D and generate STEP files for some of it" ([source](https://news.ycombinator.com/item?id=46394095))
- Python-based solid (BREP) modeling (3 comments): "I think it is much more capable than OpenSCAD due to BREP and Python." ([source](https://news.ycombinator.com/item?id=47084730)) "go straight for build123d which operates on real solid models (BREP)" ([source](https://news.ycombinator.com/item?id=47213405)) "something built on the open-source Open Cascade geometry kernel" ([source](https://news.ycombinator.com/item?id=50035553))
- Better than OpenSCAD (4 comments): "I've enjoyed Build123d (and it's over-loaded python operators) as an alternative to OpenSCAD" ([source](https://news.ycombinator.com/item?id=47092402)) "I think it is much more capable than OpenSCAD due to BREP and Python." ([source](https://news.ycombinator.com/item?id=47084730)) "I have found better results with `build123d` than with OpenSCAD" ([source](https://news.ycombinator.com/item?id=50039903))

## What people warn about

- Increasingly vibe-coded codebase (2 comments): "which has been great but is increasingly vibe-coded" ([source](https://news.ycombinator.com/item?id=47496139)) "has been great but is increasingly vibe-coded" ([source](https://news.ycombinator.com/item?id=47500135))
- Documentation is lacking (2 comments): "it's always 0. Lots of other issues/bugs too, and severely lacking in ddocumentation." ([source](https://news.ycombinator.com/item?id=46345830)) "it has a lot of issues, mainly in documentation" ([source](https://news.ycombinator.com/item?id=47503698))
- Needs lots of code (2 comments): "Build123d seems to require a lot of coding to calculate constraints and positions" ([source](https://news.ycombinator.com/item?id=50039468)) "I haven't found it as ergonomic as SolidPython" ([source](https://news.ycombinator.com/item?id=50151512))

## Alternatives hackers recommend

- [CadQuery](https://hackerapproved.com/p/cadquery.md): 40 recommend
- [BOSL2 library for OpenSCAD](https://hackerapproved.com/p/bosl2-library-for-openscad.md): 22 recommend
- [Cadova](https://hackerapproved.com/p/cadova.md): 5 recommend

## Cite as

Hacker Approved, "build123d", https://hackerapproved.com/p/build123d/ (counts from 1,795,640 Hacker News comments, November 2025 to November 2026).