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Mastering Claude Hooks: Building Observable AI Systems (Part 2)

#ai #automation #observability #claude

Picture this: It's 6 AM, you're deep in flow with Claude Code, and suddenly your AI assistant decides to be helpful by running rm -rf / on your production server.

Sound terrifying? This exact scenario is what Claude hooks were designed to prevent.

In Part 1, we explored how Claude Code is revolutionizing software development. Now, let's dive into the power tool that transforms Claude from a coding assistant into a proactive development partner: Hooks.

What Are Claude Hooks?

Hooks are event-driven scripts that fire at specific points in Claude's lifecycle. Think of them as middleware for your AI assistant - intercepting, monitoring, and enhancing every interaction.

Five hook events give you complete control:

  1. PreToolUse - Your safety guardian
  2. PostToolUse - The observer
  3. Notification - Interactive moments
  4. Stop - Session complete
  5. SubagentStop - Parallel processing

The Safety Net That Saved My Project

Last week, Claude suggested a "cleanup" operation that would've deleted my entire node_modules across all projects. Here's the hook that saved me:

#!/usr/bin/env python3
# scripts/safety_check.py

import os
import sys

DANGEROUS_PATTERNS = [
    'rm -rf /',
    'rm -rf ~',
    'sudo rm',
    ':(){:|:&};:',  # Fork bomb
    'dd if=/dev/zero',
    'chmod -R 777'
]

def check_safety():
    command = os.environ.get('TOOL_COMMAND', '')

    for pattern in DANGEROUS_PATTERNS:
        if pattern in command:
            print(f"🛑 BLOCKED: Dangerous command detected: {pattern}")
            print(f"Command was: {command}")
            sys.exit(1)  # This stops Claude from executing

    # Check for mass deletions
    if 'rm' in command and command.count('*') > 2:
        print("⚠️  Multiple wildcards in deletion command. Blocking for safety.")
        sys.exit(1)

if __name__ == "__main__":
    check_safety()
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Hook configuration:

{
  "hooks": {
    "PreToolUse": [{
      "matcher": ".*",
      "hooks": [{
        "type": "command",
        "command": "python scripts/safety_check.py"
      }]
    }]
  }
}
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This simple hook has prevented disasters multiple times. But safety is just the beginning.

Automation: Never Run Tests Manually Again

Tired of reminding Claude to run tests after changes? I built this automation chain:

#!/usr/bin/env python3
# scripts/auto_test.py

import os
import subprocess
import json

def handle_file_change():
    tool_name = os.environ.get('TOOL_NAME', '')
    file_path = os.environ.get('TOOL_FILE_PATH', '')

    if tool_name not in ['Edit', 'Write']:
        return

    # TypeScript file changed? Run type checking
    if file_path.endswith('.ts') or file_path.endswith('.tsx'):
        print("🔍 Running TypeScript checks...")
        subprocess.run(['npm', 'run', 'typecheck'], capture_output=True)

    # Test file changed? Run related tests
    if 'test' in file_path or 'spec' in file_path:
        print("🧪 Running tests...")
        subprocess.run(['npm', 'test', file_path], capture_output=True)

    # Component changed? Run component tests
    if '/components/' in file_path:
        test_file = file_path.replace('.tsx', '.test.tsx')
        if os.path.exists(test_file):
            print(f"🎯 Running component tests for {os.path.basename(file_path)}")
            subprocess.run(['npm', 'test', test_file])

if __name__ == "__main__":
    handle_file_change()
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Now every code change triggers appropriate tests automatically. No reminders needed.

Building Real-Time Observability

When you're running multiple Claude agents in parallel, observability isn't optional - it's survival. Here's my real-time monitoring system:

The Event Streaming Hook 

#!/usr/bin/env python3
# scripts/stream_event.py

import sys
import json
import requests
import os
from datetime import datetime

def stream_event():
    event_type = sys.argv[1] if len(sys.argv) > 1 else "unknown"

    # Capture all environment variables
    event = {
        'timestamp': datetime.now().isoformat(),
        'event_type': event_type,
        'session_id': os.environ.get('CLAUDE_SESSION_ID', 'unknown'),
        'tool': os.environ.get('TOOL_NAME'),
        'file_path': os.environ.get('TOOL_FILE_PATH'),
        'command': os.environ.get('TOOL_COMMAND'),
    }

    # Send to observability server (non-blocking)
    try:
        requests.post(
            'http://localhost:3000/events',
            json=event,
            timeout=0.5
        )
    except:
        pass  # Fail silently to not disrupt workflow

if __name__ == "__main__":
    stream_event()
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The Real-Time Dashboard 

// Simple Node.js server with WebSockets
const WebSocket = require('ws');
const express = require('express');
const app = express();
const server = require('http').createServer(app);
const wss = new WebSocket.Server({ server });

const events = [];
const clients = new Set();

app.post('/events', express.json(), (req, res) => {
    const event = req.body;
    events.push(event);

    // Broadcast to all connected clients
    const message = JSON.stringify({
        type: 'event',
        data: event
    });

    clients.forEach(client => {
        if (client.readyState === WebSocket.OPEN) {
            client.send(message);
        }
    });

    res.send('OK');
});

wss.on('connection', (ws) => {
    clients.add(ws);

    // Send recent history
    ws.send(JSON.stringify({
        type: 'history',
        data: events.slice(-100)
    }));

    ws.on('close', () => clients.delete(ws));
});

server.listen(3000);
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The result? A real-time view of everything Claude does:

Real-time Claude Observability Dashboard
(Dashboard showing multiple Claude agents working in parallel with activity pulse visualization)

Voice Notifications: Stay in Flow

My favorite productivity hack? Voice notifications for long-running tasks:

#!/usr/bin/env python3
# scripts/voice_notify.py

import os
import pyttsx3
from datetime import datetime

def notify():
    event_type = os.environ.get('HOOK_EVENT', '')

    engine = pyttsx3.init()
    engine.setProperty('rate', 180)

    if event_type == 'Stop':
        duration = calculate_session_duration()
        engine.say(f"Claude session complete. Duration: {duration} minutes")
    elif event_type == 'Notification':
        engine.say("Claude needs your attention")
    elif 'test' in os.environ.get('TOOL_COMMAND', ''):
        engine.say("Tests complete. Check results.")

    engine.runAndWait()

if __name__ == "__main__":
    notify()
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Now I can step away from my desk, and Claude tells me when tests finish or when input is needed.

Advanced Pattern: Multi-Agent Coordination

Running multiple Claude instances? Here's how to coordinate them:

#!/usr/bin/env python3
# scripts/agent_coordinator.py

import os
import json
import redis
from datetime import datetime

r = redis.Redis(host='localhost', port=6379, db=0)

def coordinate_agents():
    session_id = os.environ.get('CLAUDE_SESSION_ID')
    event_type = os.environ.get('HOOK_EVENT')

    if event_type == 'PreToolUse':
        # Check if another agent is working on the same file
        file_path = os.environ.get('TOOL_FILE_PATH')
        if file_path:
            current_owner = r.get(f"file_lock:{file_path}")
            if current_owner and current_owner.decode() != session_id:
                print(f"⚠️  File is being edited by another agent: {current_owner.decode()}")
                print("Waiting for lock release...")
                sys.exit(1)
            else:
                # Acquire lock
                r.setex(f"file_lock:{file_path}", 30, session_id)

    elif event_type == 'PostToolUse':
        # Release file lock
        file_path = os.environ.get('TOOL_FILE_PATH')
        if file_path:
            r.delete(f"file_lock:{file_path}")

    elif event_type == 'SubagentStop':
        # Track completion
        r.hincrby('agent_stats', 'completed_tasks', 1)

        # Notify other agents
        message = {
            'session_id': session_id,
            'status': 'completed',
            'timestamp': datetime.now().isoformat()
        }
        r.publish('agent_updates', json.dumps(message))

if __name__ == "__main__":
    coordinate_agents()
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The Complete Power Setup

Here's my production hook configuration that combines everything:

{
  "hooks": {
    "PreToolUse": [{
      "matcher": ".*",
      "hooks": [
        {
          "type": "command",
          "command": "python scripts/safety_check.py"
        },
        {
          "type": "command",
          "command": "python scripts/agent_coordinator.py"
        }
      ]
    }],
    "PostToolUse": [{
      "matcher": ".*",
      "hooks": [
        {
          "type": "command",
          "command": "python scripts/stream_event.py PostToolUse"
        },
        {
          "type": "command",
          "command": "python scripts/auto_test.py"
        },
        {
          "type": "command",
          "command": "python scripts/agent_coordinator.py"
        }
      ]
    }],
    "Notification": [{
      "matcher": ".*",
      "hooks": [
        {
          "type": "command",
          "command": "python scripts/voice_notify.py"
        },
        {
          "type": "command",
          "command": "python scripts/stream_event.py Notification"
        }
      ]
    }],
    "Stop": [{
      "matcher": ".*",
      "hooks": [
        {
          "type": "command",
          "command": "python scripts/save_session.py"
        },
        {
          "type": "command",
          "command": "python scripts/voice_notify.py"
        },
        {
          "type": "command",
          "command": "python scripts/generate_summary.py"
        }
      ]
    }],
    "SubagentStop": [{
      "matcher": ".*",
      "hooks": [
        {
          "type": "command",
          "command": "python scripts/agent_coordinator.py"
        },
        {
          "type": "command",
          "command": "python scripts/stream_event.py SubagentStop"
        }
      ]
    }]
  }
}
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The Results Are Mind-Blowing

After implementing this hook system:

  • Zero destructive commands executed (12 blocked in the last week)
  • 100% test coverage maintained automatically
  • Real-time visibility into all agent operations
  • 45% reduction in context switching thanks to voice notifications
  • Parallel agent conflicts eliminated with coordination

Performance Considerations

Keep your hooks fast! They run synchronously and can slow Claude down:

# Good: Fast, non-blocking
try:
    requests.post(url, json=data, timeout=0.5)
except:
    pass

# Bad: Slow, blocking
response = requests.post(url, json=data)
response.raise_for_status()
process_response(response.json())
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Aim for <100ms execution time per hook.

Your Turn: Start Small, Think Big

You don't need this entire system on day one. Start with:

  1. A simple safety hook to prevent disasters
  2. One automation hook for your most repetitive task
  3. Basic logging to understand Claude's patterns

Then gradually expand based on your needs.

The Future is Observable

We're moving from black-box AI to fully observable, controllable systems. Hooks are the bridge between human intent and AI execution.

In Part 3, we'll explore multi-agent orchestration - how to run 10+ Claude instances in parallel for massive productivity gains.

But don't wait - implement your first hook today. Your future self will thank you.

📚 Master AI Development at learn-agentic-ai.com

🎓 Featured Learning Paths:

📖 Related Deep-Dive Articles:

🔧 Practical Resources:

About the Author:
I'm Brandon J. Redmond, an AI Engineer specializing in observable AI systems. I've helped dozens of teams implement production-ready AI workflows. Connect on LinkedIn or visit learn-agentic-ai.com.

What repetitive tasks would you automate with hooks? Share your ideas below!

Previous: Part 1 - The Claude Code Revolution
Next: Part 3 - Multi-Agent Orchestration

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