Setup

---
description: "Verify the biome-format hook's runtime prerequisites and configuration for this repository. Use when: 'set up biome-format', 'configure biome-format', 'is biome-format working', formatting silently isn't happening, or the hook reported a missing prerequisite. Actions: check (read-only verification, default) | apply (resolve what check found). Re-runnable and safe."
argument-hint: "check | apply [install-biome]"
user-invocable: true
disable-model-invocation: true
---

## Purpose

Thin check-centric setup per the uniform setup contract (`docs/PLUGIN-PHILOSOPHY.md`
"Setup is explicit and repeatable" in the marketplace repository): `check` inspects and
reports, `apply` resolves. This plugin owns no consumer-project configuration. Rules come
from the repository's own Biome config, and the only tunable is the native `userConfig`
toggle, so `apply` is guidance-and-verify, with exactly one write path: the explicitly
invoked `apply install-biome` dependency install described below.

Action routing: no argument or `check` runs the check; `apply` runs the check first, then
remediation; `apply install-biome` additionally authorizes the consumer-repo dependency
install described below. All are non-interactive. Never prompt when the action is given.

## `check` (read-only)

The hook script (`${CLAUDE_PLUGIN_ROOT}/hooks/biome-format.sh`) is the single source of
truth for what it requires and how it resolves things.

**Read it first.** Probe what it actually does, don't recite this file. Then run each probe via
Bash and report a PASS/FAIL/INFO table with one remediation line per FAIL. Do not modify anything.

When the plugin's toggle is disabled, every prerequisite absence downgrades from FAIL to
INFO. The hook exits through its enabled-gate before probing anything, so a deliberately
disabled plugin is not broken. Report the probes informationally and note that re-enabling
restores the FAIL semantics.

1. **Bash version.** Check against the hook's documented floor (README Requirements),
   noting any features the hook degrades without (for example telemetry's `EPOCHREALTIME`,
   Bash 5.0+).
2. **`jq`.** `command -v jq`. FAIL if absent: the hook then skips with a visible
   once-per-session notice instead of formatting.
3. **Biome binary.** Resolve it exactly the way the hook's resolution code does: its
   repo-local install walk (the `node_modules/.bin` path it tests, walking up from the
   edited file toward the repo root) and then `PATH`. Test only what the hook tests. A
   binary the hook would not accept must not PASS here. FAIL when nothing the hook would
   resolve is present while a Biome config governs the repo; the hook then emits a visible
   once-per-session skip notice instead of formatting.
4. **Consumer Biome config.** Mirror the hook's opt-in walk: it records the topmost
   governing config found walking from the edited file's directory up to the repo root, and
   deliberately accepts only the config names the hook treats as the opt-in. Read the hook:
   the hidden dotted variants are intentionally excluded. Report the governing config the
   walk discovers, or INFO that none exists. Absence is the opt-out by design, so the
   plugin is inert (INFO, not FAIL), matching the README's "ships no rules of its own"
   stance.
5. **Hook toggle.** Report the effective `biome_format_enabled` value:
   `${user_config.biome_format_enabled}` (unexpanded or empty means default `true`).
6. **Hook registration.** INFO: confirm the plugin is enabled for this project
   (`/plugin` → Installed) rather than parsing settings files.

## `apply` (idempotent)

Run `check`, then for each FAIL offer the resolution. Never install anything without the
consumer's explicit go-ahead in the invocation. `apply install-biome` adds
`@biomejs/biome` as a dev dependency in the consumer repository **using the repository's
own package manager**, resolved in order: lockfile (`pnpm-lock.yaml` → `pnpm add -D`,
`yarn.lock` → `yarn add -D`, `bun.lock`/`bun.lockb` → `bun add -d`, `package-lock.json` →
`npm install --save-dev`), then the `package.json` `"packageManager"` field when no
lockfile exists, then npm only when neither signal is present. With no `package.json`, an
ambiguous multi-lockfile state, or a lockfile that contradicts `packageManager`, stop with
manager-specific guidance instead of guessing. Never introduce a competing lockfile. The
change is stated before running. For a Yarn repository, don't infer the linker. Ask the
repo's own Yarn: run `yarn config get nodeLinker` in the repo. `pnp` (Berry's default when
unset) → skip the install and give guidance, because Plug'n'Play generates a loader file,
not the `node_modules/.bin` shim the hook resolves; install `@biomejs/biome` on `PATH` or
switch the linker. `node-modules`/`pnpm`, or Yarn Classic (which has no such setting and
always materializes `node_modules`) → install. The verify-after-remediation rule below is
the backstop when an install still yields no usable shim. After ANY remediation, re-run the
relevant `check` probe and report its actual result. Never claim resolved on the install
command's exit code alone. For everything else `apply` only points:

- missing `jq` / Bash: platform install instructions from the README Requirements section;
  this skill never installs system packages.
- toggle off: direct to `/plugin configure biome-format` (interactive, any
  time). Headless: rerun the install with the new value,
  `claude plugin install biome-format@<marketplace> -s <scope> --config biome_format_enabled=true`
  (repeatable per key). Against an already-installed plugin it prints `already installed` **and
  still writes the value**, verified on Claude Code 2.1.240 (a non-sensitive option at `user`
  scope: a non-default value written to an installed plugin, then restored). The short-circuit is
  about the install, not the config write. Re-verify before relying on it outside those
  conditions. A `sensitive` option, or `project`/`local` scope, were not covered. Do **not**
  uninstall to reconfigure: uninstalling drops this plugin's entire stored `pluginConfigs` entry,
  resetting every option in the README's Options reference table to its manifest default. `-s`
  defaults to `user`, so pass the scope `claude plugin list` reports for this plugin, and run from
  that project's directory for a `project`/`local` scope, or the write lands at a scope that does
  not load. This skill never writes user settings or `pluginConfigs`.
  Afterwards, keep the two claims apart. The write is issued and the stored value is what you
  passed; the RUNNING session's behavior is not. The rendered `${user_config.*}` is injected at
  skill load and each hook receives its `CLAUDE_PLUGIN_OPTION_*` from an environment fixed at
  session start, so a same-session `check` still reports the OLD value. Reporting that as a
  failed write would be wrong. Verify the effective value by rerunning `check` in a **fresh
  session**, and never claim an unobserved change.
- no Biome config: offer to create a minimal `biome.json` in the repository root only when
  explicitly asked. The plugin imposes no rules of its own.

Re-running `apply` after everything passes changes nothing and reports "already configured".

## What this skill does NOT do

- Run the formatter. Editing any supported file exercises the hook end-to-end.
- Write the plugin cache, Claude Code user settings, or `pluginConfigs`.
- Download or execute tools during `check`; network use happens only in an explicitly
  requested `apply install-biome` inside the consumer repository.