# typelevel/fs2

Compositional, streaming I/O library for Scala

Repository: https://github.com/typelevel/fs2
Canonical: https://ross.abutalabs.com/products/fs2
Homepage: https://fs2.io
Language: Scala
License: NOASSERTION
License Family: other
Topics: scala, stream, streaming-computation, fp, functional-programming
Last push: 2026-08-24T18:08:23+00:00

## Health v2 (maintenance only)
Score: 82/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 50, longevity 100
- inputs: {"age_days": 4928, "days_push": 9, "days_rel": 174, "gap_med": 94.0, "n_releases_24m": 5}
- flags: no_license
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2451, forks 635 (observed 2026-08-28T04:06:52.948110+00:00)

## What it is
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
- artifact type: library
- maturity: active
- function: streaming, concurrency, file-system, networking
- domain: developer-tools
- platform: jvm, cross-platform
- tags: scala, streams, cats-effect, functional-programming, resource-safety, reactive-streams, data-engineering

## Member repositories
- typelevel/fs2 (main) score 82

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:52.948110+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:30:12.826306+00:00, confidence not recorded.
  - readme: https://github.com/typelevel/fs2 (fetched 2026-08-28T04:06:52.948110+00:00, sha 6888adfa255b)
  - homepage: https://fs2.io (fetched 2026-08-29T10:11:30.151047+00:00, sha 36d16d35f07c)
- Data as of 2026-08-30T08:39:29.467469+00:00.