# zio/zio

ZIO — A type-safe, composable library for async and concurrent programming in Scala

Repository: https://github.com/zio/zio
Canonical: https://ross.abutalabs.com/products/zio
Homepage: https://zio.dev
Language: Scala
License: Apache-2.0
License Family: permissive
Topics: effects, concurrency, asynchronicity, functional-programming, queues, streams, promises, stm, asynchronous, concurrent, concurrent-programming, asynchronous-programming, concurrent-data-structure, zio, scala
Last push: 2026-08-26T00:40:20+00:00

## Health v2 (maintenance only)
Score: 89/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 71, longevity 100
- inputs: {"age_days": 3028, "days_push": 8, "days_rel": 119, "gap_med": 33.5, "n_releases_24m": 17}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 4410, forks 1585 (observed 2026-08-28T04:08:48.489167+00:00)

## What it is
ZIO is a zero-dependency Scala library for type-safe, composable asynchronous and concurrent programming, built on lightweight fibers. It provides resource safety, structured concurrency, streaming, STM, and testable dependency injection in a purely functional effect system.

## Use cases
- write concurrent Scala code without deadlocks or race conditions
- build scalable async applications on the JVM
- manage resources safely with automatic acquisition and release
- process data with composable streaming pipelines
- retry and timeout failing operations declaratively
- write deterministic, type-safe tests with injected services
- perform transactional in-memory state with STM

## When to choose
- you are building Scala/JVM applications needing high-performance concurrency
- you want compile-time type safety for async and error handling
- you need resource-safe, interruption-aware parallelism
- you want a rich ecosystem (streams, testing, DI) around one effect system

## When to avoid
- your project is not on Scala or the JVM
- your team is not prepared for a functional programming learning curve
- you need a minimal single-threaded app where an effect system is overkill
- you are locked into another ecosystem like Akka or Cats Effect

## Facets
- artifact type: library
- maturity: stable
- function: concurrency, error-handling, streaming, testing, scheduling, developer-tools
- domain: developer-tools, backend, microservices
- platform: jvm, cross-platform
- tags: effect-system, fibers, functional-programming, stm, resource-safety, async, scala

## Member repositories
- zio/zio (main) score 89

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:08:48.489167+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 2026-08-29T18:21:04.040712+00:00, confidence not recorded.
  - readme: https://github.com/zio/zio (fetched 2026-08-28T04:08:48.489167+00:00, sha 941b875f7193)
  - homepage: https://zio.dev (fetched 2026-08-29T09:08:55.015220+00:00, sha a794b92febba)
  - site_page: https://zio.dev/overview/getting-started (fetched 2026-08-29T09:08:55.024388+00:00, sha 13ae7b59f065)
  - site_page: https://zio.dev/contributing-to-documentation (fetched 2026-08-29T09:08:55.026202+00:00, sha 3e6c3734d876)
  - site_page: https://zio.dev/faq (fetched 2026-08-29T09:08:55.027890+00:00, sha 4befb004f8f0)
- Data as of 2026-08-30T08:39:29.467469+00:00.