Run shell commands automatically on Claude Code events.

What it is

Hooks are shell commands Claude Code runs automatically on specific events — PreToolUse, PostToolUse, SessionStart, UserPromptSubmit, and more. Configure once and they fire in the background without Claude having to remember. Perfect for linters, tests, notifications, backups.

Install / Setup

Hooks are configured in settings.json — NOT in CLAUDE.md. CLAUDE.md holds rules, hooks are real harness config.

Option 1 — Terminal:

# Global hooks
nano ~/.claude/settings.json

# Project hooks
nano .claude/settings.json

Example settings.json:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          { "type": "command", "command": "npm run lint --silent" }
        ]
      }
    ]
  }
}

Option 2 — Prompt Claude Code:

Set up a hook: after every Edit/Write on .ts or .tsx files, run "npm run lint". Write it straight into ~/.claude/settings.json (or cleanly merge with what's already there). Then show me how to test it.

Anthropic's update-config skill helps with hook setup — the harness runs hooks, not Claude itself.

Event types (selection)

• PreToolUse — Before any tool call (Bash, Edit, Write…)
• PostToolUse — After a tool call
• SessionStart — When a Claude Code session starts
• UserPromptSubmit — When you send a prompt
• Stop — When Claude finishes a turn

Use cases

• Auto-lint on edit — PostToolUse hook on Edit/Write, runs the linter on the changed file.
• Tests on save — Changes to src/**/*.test.ts trigger the test run immediately.
• Session-start check — On start: verify the dev server is up, show git status, show the last commit.
• Commit guard — PreToolUse on Bash calls containing git commit: enforces linter/tests first.
• Telegram notification — PostToolUse: ping your phone on deploy commands.

Pro tip

Hooks can block tool calls (non-zero exit → call refused). Use that deliberately: a pre-commit hook that rejects commits on red tests is gold. But: over-eager hooks get annoying fast — if the linter blocks every edit for 5 seconds, you'll hate your setup within a day.

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