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:

Variable	When it is available
PRE_COMMIT_FROM_REF, PRE_COMMIT_ORIGIN	The starting ref for revision-range and push-style runs
PRE_COMMIT_TO_REF, PRE_COMMIT_SOURCE	The destination ref for revision-range and push-style runs
PRE_COMMIT_COMMIT_MSG_SOURCE	The commit-message source supplied by Git
PRE_COMMIT_COMMIT_OBJECT_NAME	The commit object supplied to prepare-commit-msg
PRE_COMMIT_PRE_REBASE_UPSTREAM, PRE_COMMIT_PRE_REBASE_BRANCH	pre-rebase arguments
PRE_COMMIT_LOCAL_BRANCH, PRE_COMMIT_REMOTE_BRANCH	pre-push branch values
PRE_COMMIT_REMOTE_NAME, PRE_COMMIT_REMOTE_URL	pre-push remote values
PRE_COMMIT_CHECKOUT_TYPE	The checkout flag supplied to post-checkout
PRE_COMMIT_SQUASH_MERGE	Set to 1 for a squash merge
PRE_COMMIT_REWRITE_COMMAND	The command supplied to post-rewrite

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:

Variable	Effect
SSL_CERT_FILE, SSL_CERT_DIR	Add certificate locations used by HTTPS requests
GITHUB_TOKEN	Authenticate supported GitHub API requests, including self-update and an exact GitHub Ruby mirror
HTTP_PROXY, HTTPS_PROXY, NO_PROXY and lowercase forms	Configure inherited network proxy behavior

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.