---
id: build123d
version: "0.11.1"
license: Apache-2.0
license_treatment: permissive
maintenance: active
---

# build123d — A python CAD programming library

License: permissive · Maintenance: active · Downloads: 374.6K/mo

## What it is and what it does

build123d is a Python library for writing CAD models as code using boundary representation (BREP) geometry. It wraps the Open Cascade geometric kernel and provides a clean, Pythonic interface for constructing 2D and 3D shapes through two complementary paradigms: Algebra Mode (stateless, operator-driven) and Builder Mode (state-tracked, context-aware). Both modes support creating edges, wires, faces, sketches, and solids through explicit geometry classes and algebraic operations like addition and subtraction, with selectors for filtering shapes by properties like area, length, or orientation.

The library is designed for manufacturing workflows—3D printing, CNC machining, laser cutting—and supports importing and exporting standard formats (SVG, STEP, STL). It emphasizes clean, maintainable code with minimal internal state, rich type hints, and extensibility through subclassing. The 17 runtime dependencies include numpy, scipy, and scikit-learn for numerical operations, plus specialized packages like ezdxf for DXF interchange and lib3mf for 3MF format support.

Use it for:

- Parametric part design for 3D printing: define dimensions as variables and regenerate models with different parameters.
- Laser cutting layouts: import SVG designs, convert to 2D faces, and export as DXF or STEP for cutting machines.
- CNC toolpath preparation: model complex geometries with fillets and chamfers, then export STEP for CAM software.
- Reusable component libraries: subclass geometry objects to create custom parametric parts (e.g., custom fasteners, brackets).
- Design automation: generate arrays of parts with GridLocations and conditional logic for batch manufacturing.
- Interoperability workflows: import STEP assemblies, modify specific components, and export back to FreeCAD or SolidWorks.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

build123d is a Python CAD framework for creating 2D and 3D models using boundary representation geometry, built on the Open Cascade kernel, with export to standard formats like STEP and STL.

Yes. build123d is actively maintained, has no known vulnerabilities, installs with low friction, and carries a permissive Apache-2.0 license. It is well-suited for developers who want to define CAD models programmatically rather than through a GUI. The large dependency footprint (17 packages) is typical for scientific Python and not a barrier. Start with the documentation and cheat sheet if you are new to BREP modeling or parametric CAD.

## Install

pip install build123d
uv add build123d
poetry add build123d

## Installing build123d

Before you install: Low friction installation as a pure-wheel package. Actively maintained with a recent release (43 days old) and 2854 GitHub stars. Requires Python 3.10–3.14 and pulls in 17 runtime dependencies including numpy, scipy, and scikit-learn, which are standard scientific packages.

License in practice: Apache-2.0 permissive license allows commercial and private use with minimal restrictions; you may use, modify, and distribute the code provided you include the license and copyright notice.

Quickstart:

pip install build123d

from build123d import *

line = Line((0, -3), (6, -3))
line += JernArc(line @ 1, line % 1, radius=3, arc_size=180)
sketch = make_hull(line.edges())
part = extrude(sketch, amount=2)

Requires Python 3.10 or later (up to 3.14); Open Cascade geometric kernel is a compiled dependency bundled via cadquery-ocp-novtk.

Verify before relying:

- Whether the 17 runtime dependencies (numpy, scipy, scikit-learn, etc.) are all required for basic usage or only for specific features.
- Performance characteristics and typical model complexity limits for real-world manufacturing workflows.
- Interoperability details with FreeCAD and SolidWorks export beyond the documented STEP/STL formats.

## Package facts

- License: Apache-2.0 (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 374.6K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

python cad modeling library, parametric 3d design code, brep geometry framework, 3d printing model generation, opencascade python wrapper, cad as code, step stl export, cad-as-code, 3d-modeling, manufacturing

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