Hooks / formatting

ESLint after JS/TS edit

Runs eslint --fix on JavaScript and TypeScript files after Claude edits them, and warns (never blocks) on remaining problems.

What it does

Same shape as the Prettier hook, but runs eslint --fix on .js/.jsx/.ts/.tsx files. If problems remain after fixing, the script exits 2 so Claude sees the lint output as a warning and can react - the edit itself already happened, so nothing is blocked.

When it runs

Config

Merge this into .claude/settings.json - or use the generator to combine hooks.

{
  "hooks": {
    "PostToolUse": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PROJECT_DIR}/.claude/hooks/eslint-after-edit.sh",
            "timeout": 30
          }
        ],
        "matcher": "Edit|Write"
      }
    ]
  }
}

Script

Save as .claude/hooks/eslint-after-edit.sh and chmod +x it.

#!/bin/bash
# eslint-after-edit: run after Claude edits a file. Reads hook JSON from stdin.
set -u
file=$(jq -r '.tool_input.file_path // empty')
[ -z "$file" ] && exit 0
[ -f "$file" ] || exit 0
case "$file" in
*.js|*.jsx|*.ts|*.tsx) ;;
  *) exit 0 ;;
esac
if ! command -v eslint >/dev/null 2>&1; then
  exit 0  # formatter not installed; stay silent
fi
if ! npx eslint --fix "$file" >/dev/null 2>&1; then
  echo "ESLint still reports problems in $file" >&2
  npx eslint "$file" >&2 2>/dev/null
  exit 2
fi
exit 0

Install

1. Save the script to .claude/hooks/eslint-after-edit.sh and run: chmod +x .claude/hooks/eslint-after-edit.sh
2. Install the formatter (eslint) and make sure it is on your PATH, plus jq.
3. Add the config fragment to .claude/settings.json (or use the generator).

Test it

• Positive: have Claude write a JS file with an auto-fixable lint issue (e.g. extra semicolon per your config) and confirm it gets fixed.
• Warn path: have Claude write a file with a non-fixable issue and confirm Claude sees the warning (exit 2 shows stderr to Claude after the edit).
• Negative: edit a .py file - ESLint should not run.

Sources

• Claude Code hooks reference (checked 2026-09-10)
• Claude Code hooks guide (checked 2026-09-10)

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