---
id: kiwisolver
version: "1.5.0"
license: ========================= The Kiwi licensing terms ========================= Kiwi is licensed under the terms of the Modified BSD License (also known as New or Revised BSD), as follows: Copyright (c)… (full text in the JSON record)
license_treatment: permissive
maintenance: active
---

# kiwisolver — A fast implementation of the Cassowary constraint solver

License: permissive · Maintenance: active · Popularity: top 1,000 on PyPI

## Install

pip install kiwisolver
uv add kiwisolver
poetry add kiwisolver

## Description

# Welcome to Kiwi

[![Continuous Integration](https://github.com/nucleic/kiwi/workflows/Continuous%20Integration/badge.svg)](https://github.com/nucleic/kiwi/actions)
[![Documentation building](https://github.com/nucleic/kiwi/workflows/Documentation%20building/badge.svg)](https://github.com/nucleic/kiwi/actions)
[![codecov](https://codecov.io/gh/nucleic/kiwi/branch/main/graph/badge.svg)](https://codecov.io/gh/nucleic/kiwi)
[![Documentation Status](https://readthedocs.org/projects/kiwisolver/badge/?version=latest)](https://kiwisolver.readthedocs.io/en/latest/?badge=latest)

Kiwi is an efficient C++ implementation of the Cassowary constraint solving
algorithm. Kiwi is an implementation of the algorithm based on the
[seminal Cassowary paper](https://constraints.cs.washington.edu/solvers/cassowary-tochi.pdf).
It is *not* a refactoring of the original C++ solver. Kiwi has been designed
from the ground up to be lightweight and fast. Kiwi ranges from 10x to 500x
faster than the original Cassowary solver with typical use cases gaining a 40x
improvement. Memory savings are consistently > 5x.

In addition to the C++ solver, Kiwi ships with hand-rolled Python bindings.

# How to use
## C++...

## AI interpretation — verify before relying

Kiwisolver is a fast C++ implementation of the Cassowary constraint solving algorithm, accessible via Python bindings, for solving systems of linear constraints efficiently.

Verdict: Kiwisolver is a mature, well-maintained constraint solver with broad platform support and no security issues. Its permissive Modified BSD License and active development (last commit 2026-08-04) make it suitable for production use. Medium install friction is offset by comprehensive prebuilt wheels.

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