# reactor/reactor-core

Non-Blocking Reactive Foundation for the JVM

Repository: https://github.com/reactor/reactor-core
Canonical: https://ross.abutalabs.com/products/reactor-core
Homepage: http://projectreactor.io
Language: Java
License: Apache-2.0
License Family: permissive
Topics: reactive, flux, mono, reactive-streams, flow, asynchronous, reactive-extensions, jvm
Last push: 2026-08-26T07:15:51+00:00

## Health v2 (maintenance only)
Score: 99/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 99, longevity 100
- inputs: {"age_days": 3949, "days_push": 7, "days_rel": 10, "gap_med": 27, "n_releases_24m": 36}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 5234, forks 1254 (observed 2026-08-28T04:09:13.486898+00:00)

## What it is
Reactor Core is a non-blocking reactive streams foundation library for the JVM, implementing a Reactive Extensions-inspired API with the Flux (0..N) and Mono (0..1) publisher types. It provides efficient demand management, backpressure, and high-throughput event streaming, and underpins frameworks like Spring WebFlux.

## Use cases
- build non-blocking asynchronous applications on the JVM
- handle backpressure in high-throughput event streams
- compose asynchronous data pipelines with Flux and Mono
- implement reactive microservices with Spring WebFlux
- process millions of messages per second with low memory footprint
- debug reactive code with the reactor-tools java agent

## When to choose
- you need a Reactive Streams implementation with rich operator support on the JVM
- you are building Spring Boot/WebFlux or RSocket/R2DBC-based reactive applications
- you need backpressure-ready, non-blocking concurrency without writing raw Reactive Streams
- you want a mature, well-documented library with testing utilities (reactor-test)

## When to avoid
- you want simple synchronous code and don't need non-blocking concurrency
- you target Android officially (Reactor doesn't officially support it)
- your team is unfamiliar with reactive programming and the learning cost outweighs benefits
- you need a full framework rather than a foundation library

## Facets
- artifact type: library
- maturity: stable
- function: concurrency, streaming, middleware
- domain: backend, developer-tools, microservices
- platform: jvm, cross-platform
- tags: reactive-streams, flux, mono, reactive-extensions, backpressure, non-blocking, asynchronous, spring-webflux, java, real-time

## Member repositories
- reactor/reactor-core (main) score 99

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:09:13.486898+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 2026-08-29T17:59:38.420499+00:00, confidence not recorded.
  - readme: https://github.com/reactor/reactor-core (fetched 2026-08-28T04:09:13.486898+00:00, sha c99d29db6e34)
  - homepage: http://projectreactor.io (fetched 2026-08-29T08:54:58.366584+00:00, sha dfddcb293632)
  - site_page: https://projectreactor.io/docs (fetched 2026-08-29T08:54:58.369202+00:00, sha 482fda30829b)
  - site_page: https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html (fetched 2026-08-29T08:54:58.370978+00:00, sha 10fd5a2fb999)
  - site_page: https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html (fetched 2026-08-29T08:54:58.374418+00:00, sha 75a6cfb770f2)
  - site_page: https://projectreactor.io/docs/core (fetched 2026-08-29T08:54:58.377966+00:00, sha 41782e9b9167)
  - site_page: https://projectreactor.io/docs/netty (fetched 2026-08-29T08:54:58.380868+00:00, sha 1b61684940bb)
- Data as of 2026-08-30T08:39:29.467469+00:00.