Hooks & Automation

Hooks let you run shell commands automatically in response to Claude Code events. They’re the bridge between Claude’s actions and your custom tooling.

What Are Hooks?

Hooks are shell commands that execute when specific events occur in Claude Code. Think of them like git hooks, but for AI actions.

Configuring Hooks

Hooks are defined in your settings files:

• ~/.claude/settings.json — global hooks
• .claude/settings.json — project-specific hooks

{
  "hooks": {
    "tool_call": [
      {
        "tool": "Write",
        "command": "echo 'File written: $FILE_PATH' >> /tmp/claude-log.txt"
      }
    ],
    "prompt_submit": [
      {
        "command": "echo 'Prompt submitted at $(date)' >> /tmp/claude-log.txt"
      }
    ]
  }
}

Hook Events

Event	When It Fires
tool_call	Before a tool is executed
prompt_submit	When you submit a message
session_start	When a Claude session begins

Practical Hook Examples

Auto-Format on Write

Run Prettier whenever Claude writes a file:

{
  "hooks": {
    "tool_call": [
      {
        "tool": "Write",
        "command": "npx prettier --write $FILE_PATH"
      }
    ]
  }
}

Lint Check on Edit

Run ESLint after Claude edits a JavaScript/TypeScript file:

{
  "hooks": {
    "tool_call": [
      {
        "tool": "Edit",
        "pattern": "*.{js,ts,jsx,tsx}",
        "command": "npx eslint --fix $FILE_PATH"
      }
    ]
  }
}

Audit Log

Log all Claude actions for review:

{
  "hooks": {
    "tool_call": [
      {
        "command": "echo \"$(date): $TOOL_NAME on $FILE_PATH\" >> .claude/audit.log"
      }
    ]
  }
}

Hooks vs. Skills

	Hooks	Skills
Trigger	Automatic (event-driven)	Manual (you invoke them)
Purpose	Side effects and guardrails	Complete workflows
Examples	Auto-format, lint, log	Deploy, review, commit
Scope	Individual tool calls	Multi-step processes

Use Cases

• Code quality enforcement — auto-lint and format
• Security guardrails — block writes to sensitive directories
• Logging and auditing — track what Claude does
• Integration triggers — notify Slack, update tickets
• Build validation — run type checks after edits

Exercise

1. Add a simple logging hook to your project’s .claude/settings.json
2. Run a Claude session and make some changes
3. Check the log to see what was captured
4. Add a formatting hook for your preferred language