Claude post-edit format hook

claude.settings.json

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "~/.claude/hooks/format.sh",
            "timeout": 30
          }
        ]
      }
    ],
  },
}

format.sh

#!/bin/bash
# PostToolUse hook: run prettier and/or oxfmt on edited files.
# Each formatter runs independently based on its config being present.
# Reports back to Claude only if the file was changed.

export PATH="$HOME/.volta/bin:$PATH"

FILE=$(jq -r '.tool_input.file_path // empty')
[ -z "$FILE" ] && exit 0
[ -f "$FILE" ] || exit 0

find_package_root() {
  local dir
  dir=$(cd "$(dirname "$FILE")" && pwd)
  while [ "$dir" != "/" ]; do
    [ -f "$dir/package.json" ] && echo "$dir" && return 0
    dir=$(dirname "$dir")
  done
  return 1
}

ROOT=$(find_package_root) || exit 0

has_prettier_config() {
  for f in .prettierrc .prettierrc.json .prettierrc.yml .prettierrc.yaml .prettierrc.json5 \
            .prettierrc.js .prettierrc.mjs .prettierrc.cjs \
            prettier.config.js prettier.config.mjs prettier.config.cjs .prettierrc.toml; do
    [ -f "$ROOT/$f" ] && return 0
  done
  jq -e '.prettier' "$ROOT/package.json" >/dev/null 2>&1
}

BEFORE=$(shasum -a 256 "$FILE" 2>/dev/null)

if [ -f "$ROOT/oxfmtrc.jsonc" ] || [ -f "$ROOT/oxfmt.config.ts" ]; then
  NODE_MAJOR=$(node --version 2>/dev/null | sed 's/v\([0-9]*\).*/\1/')
  [ "$NODE_MAJOR" = "20" ] && OXFMT_NODE_OPTIONS="--import @oxc-node/core/register"
  cd "$ROOT" && NODE_OPTIONS="$OXFMT_NODE_OPTIONS" pnpm exec oxfmt --write "$FILE" >/dev/null 2>&1 || true
fi

if has_prettier_config; then
  cd "$ROOT" && pnpm exec prettier --write "$FILE" >/dev/null 2>&1 || true
fi

AFTER=$(shasum -a 256 "$FILE" 2>/dev/null)

if [ "$BEFORE" != "$AFTER" ]; then
  jq -n --arg f "$FILE" \
    '{"hookSpecificOutput":{"hookEventName":"PostToolUse","additionalContext":"Formatter changed \($f) — re-read the file before continuing."}}'
fi