Buck2
Buck2 is a free build system from Meta for large-scale repositories that combine multiple programming languages.
What Buck2 is
Buck2 is a free build system from Meta for large-scale repositories that combine multiple programming languages. It uses Starlark rules, a dynamic dependency graph, and incremental actions to support extensible builds. Its language table lists prelude rules for C/C++, Erlang, Go, Haskell, Java, Kotlin, OCaml, Python, and Rust, though usability differs by language. Build actions can run remotely through services exposing Bazel's remote execution API; listed compatible services include BuildBarn, BuildBuddy, EngFlow, and NativeLink. Buck2 supports filesystem watching and can integrate with Meta's optional Eden virtual filesystem. Rules are hermetic by default, and missing dependencies cause errors, but local-only build steps are not sandboxed. The project describes Buck2 as early-stage, with no stable release tag; its latest binary tag changes with repository pushes. It cautions that outside users may encounter rough edges, missing features, and missing toolchains. Source and binaries are available under MIT and Apache-2.0 licenses, with community discussion on Discord and issue reporting through GitHub.
Good
- Supports builds across multiple languages.
- Remote execution works through Bazel's remote execution API.
- Hermetic rules treat missing dependencies as errors.
- Source and binaries are free under listed licenses.
Watch out
- The project describes Buck2 as early-stage.
- There is no stable release tag.
- Outside users may encounter missing features and toolchains.
- Local-only build steps are not sandboxed.
Who it suits
Buck2 is aimed at teams working with large, multi-language repositories that need to compose targets across languages. It may be a fit for users prepared to work with early-stage software.
Verdict
Buck2 offers a free approach to large multi-language builds, with optional remote execution. Its early-stage status and lack of a stable release make its limitations important to weigh.
Plans and prices
From Buck2's own pricing page, checked 30 Sep 2026.
| Plan | Price | What it gives you |
|---|---|---|
| Open source | Free | Buck2 build system · source and binaries available under MIT and Apache-2.0 licenses |
The facts
Each one read from Buck2's own pages, with the date it was checked.
What it does
- Audience
- Buck2 is designed for large-scale, multi-language repositories and supports composing targets across languages in one build.checked 30 Sep 2026
- Features
- Buck2 uses Starlark rules, a dynamic dependency graph, and incremental actions to support extensible builds.checked 30 Sep 2026
- Integrations
- The project says BuildBarn, BuildBuddy, EngFlow, and NativeLink work with its distributed compilation support through the Bazel Remote Execution API.checked 30 Sep 2026
- Languages
- The language support table lists C/C++, Erlang, Go, Haskell, Java, Kotlin, OCaml, Python, and Rust with available prelude rules; support usability varies by language.checked 30 Sep 2026
- Large repositories
- Buck2 supports filesystem watching and can integrate with Meta's Eden virtual filesystem, though Eden is optional.checked 30 Sep 2026
- Maturity
- The project describes Buck2 as early-stage and warns that outside users may encounter rough edges, missing features, and missing toolchains.checked 30 Sep 2026
- Purpose
- Buck2 is a large-scale, fast, hermetic, multi-language build system and the successor to Buck.checked 30 Sep 2026
- Release status
- The repository says Buck2 does not yet have a stable release tag and that its latest binary tag updates on every repository push.checked 30 Sep 2026
- Remote execution
- Buck2 can use services that expose Bazel's remote execution API to run build actions remotely.checked 30 Sep 2026
- Security and correctness
- Buck2 rules are hermetic by default and missing dependencies are errors; local-only build steps are not sandboxed, while remote execution is hermetic by design.checked 30 Sep 2026
- Support
- The project directs users to report issues through GitHub and provides a community Discord server.checked 30 Sep 2026
The company
- Maker
- Buck2 is a build system from Meta and the repository says it was designed by Meta.checked 30 Sep 2026
Where it runs
- Platforms
- The installation guide documents building from source on Linux, macOS, and Windows, and notes prebuilt protoc support on those systems.checked 30 Sep 2026
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