Prek

prek

Use this skill when the user wants to set up or run Git hooks with prek.

prek is a Rust reimplementation of pre-commit. Its main job is to run hooks that check code and repository files before commit or on demand: formatters, linters, validators, security checks, and custom project checks.

Start with the public docs

Use the LLM-oriented index first:

• llms.txt

Per that file, prefer explicit markdown docs when you need details:

• Introduction
• Installation
• Quickstart
• Common Workflows
• Configuration
• Workspace Mode
• Language Support
• Built-in Hooks
• CLI Reference
• Configuration Reference
• Environment Variable Reference
• Differences from pre-commit
• Benchmark

What prek is for

Use prek to:

• run hooks that check source code and repo contents
• install Git hook shims such as pre-commit, pre-push, and commit-msg
• run the same hook ecosystem used by pre-commit
• manage hook runtimes and toolchains for supported languages
• validate configs, update pinned hook revisions, and inspect configured hooks

Typical jobs for hooks run by prek:

• formatting and linting code
• validating YAML, JSON, TOML, XML, and similar files
• preventing merge-conflict markers, private keys, oversized files, and bad line endings

Authoring configs

For new configs, prefer prek.toml.

Important repo types:

• remote repo: normal hook repository such as https://github.com/astral-sh/ruff-pre-commit
• repo = "local": hooks defined in the current repository
• repo = "meta": config-checking hooks like check-hooks-apply, check-useless-excludes, and identity
• repo = "builtin": prek's offline Rust-native hooks

Minimal examples:

[[repos]]
repo = "https://github.com/astral-sh/ruff-pre-commit"
rev = "v0.14.3"
hooks = [
  { id = "ruff" },
  { id = "ruff-format" },
]

[[repos]]
repo = "local"
hooks = [
  {
    id = "cargo-fmt",
    name = "cargo fmt",
    language = "system",
    entry = "cargo fmt --",
    files = "\\.rs$",
  },
]

[[repos]]
repo = "builtin"
hooks = [
  { id = "trailing-whitespace" },
  { id = "check-yaml" },
]

These examples use TOML 1.1 multiline inline tables. Use [[repos.hooks]] array-of-tables if an editor or parser in the toolchain does not support that syntax yet, or when a hook has many fields such as env, pass_filenames = false, or priority.

Filtering patterns:

• regex is the most portable choice: files = "\\.rs$"
• prek also supports globs: files = { glob = "src/**/*.rs" }
• use glob lists for multiple roots: exclude = { glob = ["target/**", "dist/**"] }

Scheduling:

• smaller priority values run earlier
• hooks with the same priority can run concurrently
• priority is evaluated within one config file, not across workspace projects

Useful prek-specific hook/config fields when editing TOML:

• env for per-hook environment variables
• priority for hook ordering and concurrency
• minimum_prek_version for gating newer config features
• orphan = true to isolate a nested workspace project from parent configs

Default workflow

When adopting prek in a repository:

1. Check whether the repo already has .pre-commit-config.yaml or .pre-commit-config.yml.
2. If it does, usually keep that config and switch the commands from pre-commit to prek.
3. If migrating from pre-commit, reinstall the Git shims with prek install -f.
4. If it does not, prefer creating prek.toml for a fresh setup.
5. Install prek.
6. Validate the config with prek validate-config.
7. Install the Git shims and prepare hook environments with prek install --prepare-hooks.
8. Run everything once with prek run --all-files.
9. For monorepos, consider nested configs, .prekignore, and orphan: true.

If the user explicitly wants maximum upstream portability, stay with .pre-commit-config.yaml and avoid prek-only keys.

Install and run

Common install methods:

• uv tool install prek
• brew install prek
• mise use prek
• cargo binstall prek
• cargo install --locked prek

Command guide

• prek install: install Git hook shims into the repo's effective hooks directory
• prek prepare-hooks: prepare hook environments without installing Git shims
• prek install --prepare-hooks: install shims and prepare environments in one step
• prek run: run hooks for the current staged file selection
• prek run --all-files: run hooks across the whole repository
• prek run <hook-id>: run only one hook
• prek list: list discovered hooks and projects
• prek validate-config: validate prek.toml or .pre-commit-config.yaml
• prek auto-update: update pinned hook revisions
• prek util yaml-to-toml: convert an existing YAML config to prek.toml
• prek util identify <path>: inspect file tags when types, types_or, or exclude_types do not match as expected

Useful quality-of-life commands and options mentioned in the docs:

• prek run --dry-run
• prek run --directory <dir>
• prek run --last-commit
• prek run --skip <hook-or-project>
• prek -C <dir> ...

For debugging:

• prek run -vvv
• PREK_NO_FAST_PATH=1 prek run: compare builtin fast-path behavior against the standard execution path
• Check the Environment Variable Reference for PREK_* controls such as PREK_HOME, PREK_SKIP, and concurrency limits.

Built-in hook guidance

prek has two important builtin paths:

• automatic fast path for supported hooks from https://github.com/pre-commit/pre-commit-hooks
• explicit repo: builtin for offline, zero-setup built-in hooks

Reach for repo: builtin when speed, no-network setup, or minimal bootstrapping matters more than upstream pre-commit compatibility.

Builtin hooks called out by the docs include:

• trailing-whitespace
• check-added-large-files
• check-case-conflict
• check-illegal-windows-names
• end-of-file-fixer
• file-contents-sorter
• fix-byte-order-marker
• check-json
• check-json5
• pretty-format-json
• check-toml
• check-vcs-permalinks
• check-yaml
• check-xml
• mixed-line-ending
• check-symlinks
• destroyed-symlinks
• check-merge-conflict
• detect-private-key
• no-commit-to-branch
• check-shebang-scripts-are-executable
• check-executables-have-shebangs

Practical guidance for agents

• Prefer prek.toml for new setups.
• Prefer existing .pre-commit-config.yaml for migrations unless the user asks for TOML.
• Reach for workspace mode in monorepos instead of forcing one giant root-only config.
• Consider repo: builtin when offline or zero-setup hooks are useful.
• If the repo already uses pre-commit-hooks, remember that prek can use built-in Rust implementations for some common hooks.
• Start with a small default hook set, then add language-specific hooks the project already uses.
• Use prek util yaml-to-toml instead of hand-converting YAML when migrating.
• Before promising parity for a specific hook language, verify it in Language Support.