# facebook/folly

An open-source C++ library developed and used at Facebook.

Repository: https://github.com/facebook/folly
Canonical: https://ross.abutalabs.com/products/folly
Language: C++
License: Apache-2.0
License Family: permissive
Last push: 2026-08-27T00:12:17+00:00

## Health v2 (maintenance only)
Score: 95/100 (v2, computed 2026-09-03T02:39:23.370411+00:00)
- activity 99, release rhythm 87, longevity 100
- inputs: {"age_days": 5206, "days_push": 7, "days_rel": 9, "gap_med": 7, "n_releases_24m": 100}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 30507, forks 5864 (observed 2026-08-28T04:11:54.504906+00:00)

## What it is
Folly is Facebook's open-source C++20 component library containing a wide range of practical, performance-oriented building blocks used extensively at Meta. It complements std and Boost by providing components that are unavailable elsewhere or that meet stricter performance profiles at large scale.

## Use cases
- high-performance C++ string and data structures
- concurrency primitives and synchronization utilities for C++
- fast serialization and memory-efficient containers
- shared foundation library for large C++ codebases
- replace Boost components with faster alternatives

## When to choose
- you need battle-tested, performance-tuned C++ components at large scale
- you are building other C++ libraries or services that depend on Facebook open-source projects
- std or Boost components do not meet your performance requirements

## When to avoid
- you want a small, focused dependency rather than a broad utility collection
- your project targets older C++ standards than C++20
- you need stable, long-term API guarantees for experimental folly modules

## Facets
- artifact type: library
- maturity: stable
- function: concurrency, developer-tools, serialization, caching
- domain: developer-tools, performance
- platform: cpp, windows
- tags: c++20, facebook, performance, core-library, boost-alternative, algorithms, linux, macos

## Member repositories
- facebook/folly (main) score 95

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:11:54.504906+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 2026-08-29T16:52:45.261024+00:00, confidence not recorded.
  - readme: https://github.com/facebook/folly (fetched 2026-08-28T04:11:54.504906+00:00, sha 3fe5cfaed2b1)
- Data as of 2026-08-30T08:39:29.467469+00:00.