typelevel/fs2

Health v2 · maintenance only

Flags: no_license

Adoption not part of the score

2451 stars · 635 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

FS2 (Functional Streams for Scala) is a purely functional, effectful stream processing library for Scala built on Cats and Cats-Effect. It emphasizes compositionality, resource safety, and performance, supporting Scala 2.12/2.13/3 as well as Scala.js and Scala Native.

Use cases

• process large files as streams in scala without loading everything into memory
• build concurrent pipelines with backpressure in scala
• stream data from kafka or tcp sockets functionally
• handle resource-safe io with guaranteed cleanup in cats-effect apps
• transform and compose effectful data streams lazily
• implement streaming etl jobs in scala

When to choose

• you are in the Typelevel/Cats-Effect ecosystem and need composable streaming
• you need resource-safe, backpressured concurrent pipelines on JVM, JS, or Native
• you want a mature, well-documented streaming library with a large ecosystem of integrations

When to avoid

• you use ZIO rather than Cats-Effect (consider zio-streams instead)
• you need simple one-shot async sequences rather than streaming (fs2 may be overkill)
• your project is not Scala-based

Facets

library · maturity active

streaming concurrency file-system networking developer-tools jvm cross-platform scala streams cats-effect functional-programming resource-safety reactive-streams data-engineering

Member repositories

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