build123d
Python based parametric BREP modeling framework for 2D and 3D CAD, built on the Open Cascade kernel for CAD as code workflows.
What it does and how it connects
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 Pythonic interface for creating precise models for 3D printing, CNC machining, laser cutting, and other manufacturing processes.
It offers two interfaces: an Algebra Mode where each object is explicitly tracked and mutated with operators, and a Builder Mode where state is tracked in Build contexts in a design-history style. Geometry is organized into explicit 1D, 2D, and 3D classes (edges and wires, faces and sketches, solids and parts), with selectors for finding features by properties such as area or geometry type, and operations including fillet, chamfer, extrude, and hole patterns.
Models interchange with other tools through import and export of STEP, STL, and SVG files, and the README notes export formats for FreeCAD and SolidWorks. It installs from pip, and the README recommends pairing it with a viewer such as ocp_vscode. The project states it is derived from portions of CadQuery but extensively refactored into an independent framework.
What engineers report
This script results in geometry that has the edges of the subtract intact, but the subtract seems to have silently failed and has a missing face too.
2026-11-04Read the original
Alternatives
Compare side by side- CadQuery
CadQuery is a Python module for building parametric 3D models with workplanes and scripted operations, while build123d offers algebra and builder modes with explicit 1D, 2D, and 3D geometry classes.
- FreeCAD
FreeCAD is a full GUI parametric 3D modeler with workbenches for sketching, FEA, CAM, and BIM, rather than a Python code library.
- OpenSCAD
OpenSCAD creates solid 3D objects from script files using constructive solid geometry, rather than a Python BREP framework on the Open Cascade kernel.
- SolidWorks
SolidWorks is a commercial parametric 2D and 3D CAD product with integrated simulation and data management, rather than a code library.
Sources
Not verified
- Pricing: none stated on the repo or docs as read.
- Related Error Index entries: no entry with software build123d was verified.
- A named individual builder beyond the repository owner handle gumyr
Last verified November 6, 2026. Listings are informational. The evidence score measures public, verifiable evidence and is not an endorsement or a compatibility claim.