build123d
Python library for code-based parametric CAD, built on the OpenCascade kernel.
Liked as a Python code-CAD library that pairs well with LLM coding assistants123 and builds real BREP solid models rather than meshes like OpenSCAD,45 with commenters using it for 3D printing prototypes and CNC-cut parts.67 The most common caveat is that AI models still struggle to write correct geometry scripts for it.89
Why people recommend it
Works with LLMs · 3
Commenters say LLM assistants handle build123d well and make a useful iteration loop for modeling.
“I have been using these models to make 3d models with build123d — they are great at it.”
“It's really useful to get an iteration loop going with an LLM.”
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“I use build123d + blender”
Real solid models · 2
Recommended over mesh-based OpenSCAD because it works on BREP solids via the OpenCascade kernel.
“go straight for build123d which operates on real solid models (BREP)”
“I've enjoyed Build123d (and it's over-loaded python operators) as an alternative to OpenSCAD”
Physical fabrication · 2
Used to prototype 3D prints and produce STEP files that were CNC cut into working parts.
“CadQuery and build123d have been very handy for prototyping stuff for 3d printing.”
“Build123d (and CadQuery) are fantastic”
Python API · 1
Commenters enjoy its Python interface, including its overloaded operators.
“I've enjoyed Build123d (and it's over-loaded python operators) as an alternative to OpenSCAD”
Over CadQuery · 1
One commenter advises choosing build123d over CadQuery.
Caveats and dissent
AI accuracy · 2
LLMs still often fail to generate correct scripts and have a poor sense of geometric relationships.
“CadQuery and build123d have been very handy for prototyping stuff for 3d printing.”
“go straight for build123d which operates on real solid models (BREP)”
Not native CSG · 1
One commenter is more excited about libfive's native constructive modeling than modeling built on edge and face representations.
“I've enjoyed Build123d (and it's over-loaded python operators) as an alternative to OpenSCAD”
Often compared with
1 moved from OpenSCAD to build123d
1 moved from Fusion 360 to build123d
1 moved from build123d to Zoo
Who recommends it in their own words
Threads where it came up
- CadQuery is an open-source Python library for building 3D CAD models 2 mentions
- OpenSCAD the Programmers Solid 3D CAD Modeller 1 mention
- Claude Haiku 5.5 1 mention
- Run Qwen 3.8 Flash Next (125B) on consumer hardware (RTX 4090) at 100T/s 1 mention
- CAD in Codex 1 mention
- Build123d: A Python CAD programming library 1 mention
Also written as Build123d. Data: build123d.json. Quotes are verbatim; the verdict and theme labels are written by a model from these comments, and every clause links to its sources.
All comments 9
“I have dabbled with build123d”
“I have been using these models to make 3d models with build123d — they are great at it.”
“I use build123d + blender”
“Use build123d > cadquery.”
“Build123d (and CadQuery) are fantastic”
“CadQuery and build123d have been very handy for prototyping stuff for 3d printing.”
“It's really useful to get an iteration loop going with an LLM.”
“go straight for build123d which operates on real solid models (BREP)”
“I've enjoyed Build123d (and it's over-loaded python operators) as an alternative to OpenSCAD”