build123d — The Complete Guide: Free Parametric CAD Written in Python Code
build123d is an open-source Python library (Apache-2.0) for parametric BREP CAD on the Open Cascade kernel. Instead of drawing with the mouse, you write the part in code: change one parameter and you get a new version of the whole part family.
build123d
build123d developers (gumyr)
Parametric CAD in Python code on the OpenCascade kernel — solid parts and assemblies exported to STEP and STL.
Get it from the vendorWhat you get
- Real solid geometry — sketches, extrusions, revolves, chamfers and fillets.
- Convenient selectors — pick faces and edges by direction, position or type.
- STEP and STL export — for further work in another CAD program or for printing.
- Automation — generate dozens of variants from a parameter table.
- Version control — the model is a text file that works well with Git.
build123d or CadQuery?
build123d was originally derived from CadQuery and restructured into an independent framework with its own syntax. Both rely on the same kernel and export STEP. Anyone used to CadQuery will find familiar concepts. Either way, you need to be comfortable with programming.
Related tools
For code-based modelling in a dedicated language — OpenSCAD. For interactive modelling with a history tree — FreeCAD. For writing the scripts themselves — Python.
CadQuery
CadQuery Project
Parametric CAD scripted in Python, on a proper solid-modelling kernel.
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OpenSCAD
OpenSCAD
Code-based 3D modelling where every dimension is a real parameter. Popular in 3D printing.
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FreeCAD
FreeCAD Project
Open-source parametric 3D modeller with workbenches for solid modelling, FEM, drafting and BIM.
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Python
Python Software Foundation
The language behind most modern engineering computation, and its full ecosystem.
Get it from the vendorThe bottom line
build123d suits engineers who produce part families or want CAD inside an automated workflow — free, open and producing standard STEP files.