Build123d: A Python CAD programming library

Summary

Documentation | Cheat Sheet | Discord | Discussions | Issues | Contributing 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. 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, Export formats to popular CAD tools such as FreeCAD and SolidWorks. Although wildcard imports are generally bad practice, build123d scripts are usually self contained and importing the large number of objects and methods into the namespace is common: Edges, Wires (multiple connected Edges), and Curves (a Compound of Edges and Wires) are the 1D Shapes available in build123d. A single Edge can be created from a Line object with two vector-like positions: line = Line((0, -3), (6, -3)) Additional Edges and Wires may be added to (or subtracted from) the initial line. These objects can reference coordinates along another line through the position (@) and tangent (%) operators to specify input Vectors: line += JernArc(line @ 1, line % 1, radius=3, arc_size=180) line += PolarLine(line @ 1, 6, direction=line % 1) Faces, Shells (multiple connected Faces), and Sketches (a Compound of Faces and Shells) are the 2D Shapes available in bui...