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use a practical, performance-focused collection of C++20 core components developed for large-scale Meta systems

OSS scale score 318.0OSS health 93Update pace 394 commits/30d
About these scores

OSS scale score is an unbounded metric that log-compresses and weights Stars, Watchers, Forks, and Contributors. Discovery score is the current OSS scale score minus the score at discovery. Update pace is commits in the last 30 days, growth momentum is the OSS scale score difference within the recent observation window, and OSS health is a 0–100 rating based on available recency, Community Health, and release data.

Stars
30,551
Primary language
C++
License
Apache-2.0
Repository last updated
Oct 3, 2026
On this page

Overview

Folly is a collection of C++20 components developed and used at Meta. It complements std and Boost by adding utilities that are unavailable there or do not meet the required performance profile, and it is a shared dependency for several Meta open-source C++ projects.

Features and best fit

Based on official documentation; not hands-on tested · Content checked:

Key features

Complement the C++ standard library and Boost with core utilities

Folly adds components when equivalent functionality is missing from the standard library or Boost, or does not satisfy the required performance characteristics.

Sources: [1]

Use implementations designed around performance at large scale

The README identifies large-scale performance as a common theme across low-level components such as synchronization, containers, memory, async, and networking utilities.

Sources: [1]

Build with CMake while fetching missing dependencies

The current CMake workflow can fetch dependencies not found on the host, enabling a release checkout to be configured and built with standard CMake commands. getdeps.py is available for CI and sibling-project workflows.

Sources: [1]

Best fit

Fits high-performance C++ services and system components needing shared utilities

It is useful when performance-sensitive C++ systems need data structures, concurrency, networking, or low-level utilities beyond the standard library.

Sources: [1]

Before adoption

Do not assume ABI compatibility between commits

The README explicitly provides no ABI compatibility guarantee from commit to commit and generally recommends static builds. Pin the Folly release/tag together with its dependency graph.

Sources: [1]

Do not treat folly/experimental as stable client API

The experimental subtree may be used internally but is not considered stable enough for client code, and updates may break consumers.

Sources: [1]

Review bundled third-party licenses separately

The project root is Apache-2.0, while the LICENSE file also records separate terms for bundled sources such as folly/external/farmhash. Preserve the relevant notices when redistributing.

Sources: [3]

Official sources

  1. [1]Folly v2026.09.28.00 README(2026-10-04)
  2. [2]Folly v2026.09.28.00 release(2026-10-04)
  3. [3]Folly Apache-2.0 and bundled notices(2026-10-04)
Supplemental curator note

Folly does not guarantee ABI compatibility from commit to commit, and its README generally recommends static builds. Pin a release/tag and reproduce its dependency graph together. Code under folly/experimental is not considered stable for client use.

Try it in 3 steps

  1. 1

    Fetch the Folly release source

    Pin the source checkout to the dated release tag.

    git clone --depth 1 --branch v2026.09.28.00 https://github.com/facebook/folly.git folly-2026.09.28
  2. 2

    Configure CMake without tests or benchmarks

    CMake may fetch dependencies that are not available on the host. Keep the validation in a local build directory instead of installing system-wide.

    cmake -S folly-2026.09.28 -B folly-2026.09.28/_build -DBUILD_TESTS=OFF -DBUILD_BENCHMARKS=OFF
  3. 3

    Build the Folly library target

    Validate that the pinned source builds without a system install. Since Folly does not guarantee ABI compatibility, pin consumers to the same release.

    cmake --build folly-2026.09.28/_build --target folly -j2
Check the official README

Growth

Growth trends · Last 30 days

30,551 Stars

Trend data is still being collected.

Development activity

Last 90 days · weekly

Commits (last 30 days)
394
Open PRs
151

Development activity is still being collected.

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GitHub data

GitHub dataView detailed GitHub data
View on GitHub
Stars
30,551
Forks
5,875
Watchers
996
Open issues
330
Contributors
277
Owner type
Organization
Primary language
C++
License
Apache-2.0
Repository last updated
Oct 3, 2026
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