Environment Variable Reference¶

prek supports the following environment variables:

prek variables¶

PREK_HOME¶

Override the prek data directory (caches, toolchains, hook envs). If beginning with ~, it is expanded to the user's home directory. Defaults to ~/.cache/prek on macOS and Linux, and %LOCALAPPDATA%\prek on Windows.

PREK_COLOR¶

Control colored output: auto (default), always, or never.

PREK_QUIET¶

Control quiet output mode. Set to 1 for quiet mode (equivalent to -q, only shows failed hooks), or 2 for silent mode (equivalent to -qq, no output to stdout).

PREK_SKIP¶

Comma-separated list of selectors to skip. A selector can be a hook ID, a project path ending in /, or a project-qualified hook such as frontend:eslint. For example, PREK_SKIP=ruff,frontend/ skips every ruff hook and the frontend project. See Skipping Projects or Hooks for details.

PREK_ALLOW_NO_CONFIG¶

Allow running without a configuration file (useful for ad-hoc runs).

PREK_NO_CONCURRENCY¶

Disable hook and batch parallelism during prek run. If set, force PREK_CONCURRENT_HOOKS and PREK_CONCURRENT_BATCHES to 1.

PREK_CONCURRENT_HOOKS¶

Set the maximum number of hooks that can run at once during prek run (minimum 1). Defaults to the number of CPU cores when unset. Ignored when PREK_NO_CONCURRENCY is set.

PREK_CONCURRENT_BATCHES¶

Set the maximum number of batches that each hook can run at once during prek run (minimum 1). A batch is one hook command invocation over a subset of the matched filenames. Defaults to the number of CPU cores when unset. Ignored when PREK_NO_CONCURRENCY is set.

PREK_NO_FAST_PATH¶

Disable Rust-native built-in hooks; always use the original hook implementation. See Built-in Fast Hooks for details.

PREK_UV_SOURCE¶

Choose one source for installing uv, the Python package installer. Options:

• astral (download from Astral's CDN)
• github (download from GitHub releases)
• pypi (install from PyPI)
• tuna (use Tsinghua University mirror)
• aliyun (use Alibaba Cloud mirror)
• tencent (use Tencent Cloud mirror)
• pip (install via pip)
• a custom PyPI mirror URL

If not set, prek tries Astral's CDN, PyPI and its configured mirrors, then pip until one succeeds. The github source is used only when selected explicitly.

PREK_NATIVE_TLS¶

Use the system trusted store instead of the bundled webpki-roots crate.

PREK_DOWNLOAD_CHECKSUM_POLICY¶

Control checksum verification for managed toolchain downloads that use checksum sidecar files. Options:

• warn-missing (default): verify downloads when a checksum is available; warn and continue when checksum metadata is missing
• required: require the checksum sidecar to be available and valid
• disabled: skip checksum fetching and verification

Checksum mismatches are hard errors whenever verification is enabled.

PREK_CONTAINER_RUNTIME¶

Specify the container runtime to use for container-based hooks (e.g., docker, docker_image). Options:

• auto (default, auto-detect available runtime)
• docker
• podman
• container (Apple's Container runtime on macOS, see container)

PREK_DOCKER_NO_INIT¶

Disable passing the runtime's --init flag when running docker and docker_image hooks. This is a compatibility escape hatch for container environments that cannot run the init helper. Disabling --init can leave containers running after Ctrl-C if the container's PID 1 does not handle forwarded signals.

PREK_RUBY_MIRROR¶

Override the Ruby installer base URL used for downloaded Ruby toolchains (for example, when using mirrors or air-gapped CI environments). Mirrors should provide release-compatible Ruby archive assets and a SHA256SUMS asset in the same release download location. Only exact HTTPS GitHub repository mirrors (https://github.com/owner/repo, optionally with port 443) receive GITHUB_TOKEN; other mirrors are used without GitHub authentication. See Ruby language support for details.

PREK_CONDA_INSTALLER¶

Select the preinstalled tool used to create environments for language: conda hooks. Supported values are auto, pixi, micromamba, mamba, and conda. The default is auto, which searches for pixi, micromamba, mamba, then conda. This setting only affects newly created environments; existing matching environments are reused without requiring the selected installer to remain available. prek does not install these tools. See Conda language support for details.

PREK_RUST_PROFILE¶

Override the rustup profile used when installing managed Rust toolchains (minimal, default, or complete). Defaults to minimal. Set to default to include rustfmt and clippy. See Rust language support for details.

PREK_USE_CARGO_BINSTALL¶

Use a preinstalled cargo-binstall for crates.io cli: dependencies of language: rust hooks. prek does not install cargo-binstall or override its telemetry and strategy settings. See Rust language support for installations that continue to use Cargo.

Compatibility fallbacks¶

PRE_COMMIT_ALLOW_NO_CONFIG¶

Fallback for PREK_ALLOW_NO_CONFIG.

PRE_COMMIT_NO_CONCURRENCY¶

Fallback for PREK_NO_CONCURRENCY.

SKIP¶

Fallback for PREK_SKIP.

Variables exposed to hooks¶

prek exports PRE_COMMIT=1 to hook processes. It also exports the following variables when the selected Git stage supplies the corresponding value:

These values describe the current hook invocation. Hooks should tolerate a variable being absent when they also support stages where Git does not provide that value.

Related external variables¶

prek also honors variables owned by Git, ecosystem tools, or its HTTP stack:

Language installers also inherit relevant ecosystem variables, such as UV_* for Python hook setup. Review unexpected ambient variables when installation behavior differs between a developer machine and CI.