http4s/http4s

Health v2 · maintenance only

Adoption not part of the score

2626 stars · 814 forks observed · 2026-08-28

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

Http4s is a minimal, idiomatic Scala library for building HTTP servers and clients, serving as Scala's equivalent to Rack, WSGI, WAI, and Servlets. It favors typeful, purely functional programming built on cats-effect and FS2 streaming, and cross-builds for Scala.js and Scala Native.

Use cases

• build http services in scala
• serve rest apis with functional scala
• make http client requests from scala
• stream large payloads over http in constant memory
• implement websockets in scala
• share http code across jvm, js, and native

When to choose

• you want a type-safe, purely functional http stack in Scala
• you already use cats-effect, fs2, or the Typelevel ecosystem
• you need streaming request/response bodies or websockets
• you want to cross-compile http code to Scala.js or Scala Native

When to avoid

• you prefer imperative or non-functional Scala http frameworks
• you need a batteries-included full-stack framework rather than a minimal http interface
• your team is unfamiliar with cats-effect and effect systems

Facets

library · maturity stable

http-server http-client web-framework middleware routing websocket streaming web-development backend apis jvm cross-platform scala cats-effect fs2 typelevel functional-http scalajs scala-native functional-programming web-server

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