typelevel/cats

Health v2 · maintenance only

Flags: no_license

Adoption not part of the score

5469 stars · 1244 forks observed · 2026-10-01

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-29, confidence not recorded

Cats is a lightweight, modular, and extensible Scala library providing abstractions for functional programming, such as type classes (Functor, Monad, Applicative) and pure data types. It aims to be a stable, binary-compatible foundation for an ecosystem of pure, typeful Scala libraries, running on JVM, Scala.js, and Scala Native.

Use cases

• use type classes like Monad and Functor in Scala
• write pure functional Scala code
• model errors with validated and Either
• build a pure FP library ecosystem on a stable core
• learn functional programming abstractions in Scala
• replace Scalaz with a modular FP foundation

When to choose

• you are doing functional programming in Scala and want lawful, modular type classes
• you need a stable, binary-compatible FP core for Scala libraries
• you want cross-building support across JVM, Scala.js, and Scala Native

When to avoid

• you want a batteries-included FP standard library with IO/Task included (look at Cats Effect or ZIO)
• your project is imperative/OO Scala with no interest in FP abstractions
• you need a runtime effect system rather than pure abstractions

Facets

library · maturity stable

type-system developer-tools programming-languages developer-tools jvm cross-platform functional-programming typeclasses category-theory scala scalajs scala-native pure-fp algorithms

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