Cats is a functional programming library for Scala that provides abstractions grounded in category theory.
Scala's hybrid object-oriented and functional nature means its standard library does not prioritize functional patterns. Cats addresses this by offering a focused set of abstractions designed for functional programming: monads, functors, applicatives, and other algebraic structures. The library emphasizes modularity so you can adopt only the pieces you need, binary compatibility to avoid breaking changes, and efficiency to keep overhead minimal. The approach makes functional programming patterns accessible without requiring deep knowledge of category theory.
Cats suits Scala projects that want to build on solid functional foundations. It works well for teams already committed to functional style or those gradually introducing functional patterns into existing codebases. The library is designed to be approachable, meaning the abstractions are usable without formal mathematical background. The project explicitly positions itself as a foundation for an ecosystem of pure, typeful libraries, so adoption opens access to downstream tools built on Cats' abstractions.
The project maintains a contributor guide and labels beginner-friendly issues to onboard new developers. The maintainers accept financial contributions through sponsorship tiers to support office hours, documentation, and strategic work. The community actively welcomes contributions and has established structures to help people get involved.
