Build123d is a Python-based, parametric boundary representation (BREP) modeling framework for 2D and 3D CAD. Built on the Open Cascade geometric kernel, it provides a clean, fully Pythonic interface for creating precise models suitable for 3D printing, CNC machining, laser cutting, and other manufacturing processes. Models can be exported to popular CAD tools such as FreeCAD and SolidWorks.

Designed for modern, maintainable CAD-as-code, build123d combines clear architecture with expressive, algebraic modeling. It offers:

• Minimal or no internal state depending on mode,
• Explicit 1D, 2D, and 3D geometry classes with well-defined operations,
• Extensibility through subclassing and functional composition—no monkey patching,
• Standards-compliant code (PEP 8, mypy, pylint) with rich pylance type hints,
• Deep Python integration—selectors as lists, locations as iterables, and natural conversions (Solid(shell), tuple(Vector)),
• Operator-driven modeling (obj += sub_obj, Plane.XZ * Pos(X=5) * Rectangle(1, 1)) for algebraic, readable, and composable design logic.

The result is a framework that feels native to Python while providing the full power of OpenCascade geometry underneath.

The documentation for build123d can be found at readthedocs.

There is a Discord server (shared with CadQuery) where you can ask for help in the build123d channel.

The recommended method for most users to install build123d is:

pip install build123d

To get the latest non-released version of build123d one can install from GitHub using one of the following two commands:

Linux/MacOS:

python3 -m pip install git+https://github.com/gumyr/build123d

Windows:

python -m pip install git+https://github.com/gumyr/build123d

If you receive errors about conflicting dependencies, you can retry the installation after having upgraded pip to the latest version with the following command:

python3 -m pip install --upgrade pip

Development install:

git clone https://github.com/gumyr/build123d.git
cd build123d
python3 -m pip install -e .

Further installation instructions are available (e.g. Poetry) see the installation section on readthedocs.

Attribution:

Build123d was originally derived from portions of the CadQuery codebase but has since been extensively refactored and restructured into an independent system.