Hooks and Extensibility

The Problem: Repeating Setup Every Session

You're working on a project. Every time you start a new Claude Code session, you manually:

1. Explain the project structure
2. Remind Claude about your naming conventions
3. Load environment variables
4. Set up project context

By the third session today, you're frustrated. Why can't Claude Code just do this automatically when a session starts?

That's what hooks solve.

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What Are Hooks?

Definition: Hooks are automated scripts that run when specific events occur in Claude Code—like when a session starts, a file is edited, or a tool runs.

Think of hooks as: Event listeners that trigger actions automatically.

A hook has three parts:

1. Event: What triggers the hook (like "SessionStart")
2. Condition (optional): Which tools or files match
3. Action: What command runs automatically

Key benefit: Automate repetitive tasks so you focus on creative work, not setup.

💬 AI Colearning Prompt

"Explain what hooks are in Claude Code. Give 2-3 real-world examples where a hook would save time by automating a repetitive task."

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Hook Events: When Hooks Trigger

Claude Code recognizes four main event types that can trigger hooks:

PreToolUse

Fires before Claude Code runs a command or tool.

Example use case: Validation hook that checks requirements before running a build script.

PostToolUse

Fires after Claude Code completes a command or tool.

Example use case: Format code immediately after edit, or run tests after saving.

SessionStart

Fires when you open a Claude Code session.

Example use case: Load environment variables, initialize project context, or run startup checks.

SessionEnd

Fires when you close a Claude Code session.

Example use case: Cleanup tasks, save session logs, or sync project state.

🎓 Expert Insight

In AI-driven development, hooks automate the routine follow-ups that developers used to do manually. Your value isn't in running npm test after every edit—it's in understanding WHEN testing matters and what the results tell you about your design.

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Real-World Hook Examples

Here are three practical scenarios showing hooks in action:

Scenario	Hook Type	Event Trigger	Action	Benefit
Code Formatting	PostToolUse	After Claude edits a .py file	Run black --line-length 88 file.py	Consistent code style without manual intervention
Test Validation	PostToolUse	After any changes to src/ directory	Run pytest and report results	Catch bugs immediately instead of later
Environment Setup	SessionStart	When new Claude Code session opens	Load variables from .env and run source setup.sh	Project context always ready without manual setup

Each hook saves time by automating what you would otherwise do manually after specific events.

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Why Hooks Matter for Professional Workflows

Imagine you're part of a development team. Without hooks:

• After every edit, someone manually runs formatters: repetitive, error-prone
• Tests run on a schedule instead of immediately: bugs discovered late
• Setup requires manual steps: onboarding takes longer

With hooks:

• Code automatically formatted immediately after edit
• Tests run automatically whenever code changes
• Project environment auto-loads on session start

Hooks are about automating the predictable parts of your workflow so you focus on the strategic thinking—the parts only humans can do.

🤝 Practice Exercise

Think of a repetitive task you've done recently (running tests, formatting code, deploying, checking linting). Ask your AI: "In Claude Code, how would a hook help automate this repetitive task? What event would trigger it?"

Expected Outcome: You'll understand how hooks map to your real workflows and why automation matters for productivity.

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Hands-On: Create Your First Hook

Let's create a simple SessionStart hook that displays a welcome message when you open Claude Code.

Step 1: Create Settings File

Hooks are configured in .claude/settings.json. Create this file in your project:

mkdir -p .claude
touch .claude/settings.json

Step 2: Add a SessionStart Hook

Edit .claude/settings.json and add:

{
  "hooks": [
    {
      "event": "SessionStart",
      "type": "command",
      "command": "echo 'Welcome to your project! Claude Code session started.'"
    }
  ]
}

What this does:

• event: Triggers when session starts
• type: "command" means run a bash command
• command: The actual command to run (echo a welcome message)

Step 3: Test Your Hook

Close and restart Claude Code in this project:

exit  # if already in a session
claude

What you should see:

Welcome to your project! Claude Code session started.

The hook ran automatically when the session started!

Step 4: Make It More Useful

Update .claude/settings.json to show project info:

{
  "hooks": [
    {
      "event": "SessionStart",
      "type": "command",
      "command": "echo 'Project: $(basename $(pwd)) | Files: $(ls -1 | wc -l) | Last modified: $(ls -lt | head -2 | tail -1 | awk \"{print \\$6, \\$7, \\$8}\")'"
    }
  ]
}

Restart Claude Code:

exit
claude

Now you see:

Project: my-project | Files: 15 | Last modified: Nov 14 10:23

Useful project context automatically every session!

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Common Questions About Hooks

"Aren't hooks the same as Skills or Plugins?"

No—each serves a different purpose:

• Hooks: Automate Claude Code's behavior in response to events (like "format code after edit")
• Skills: Extend Claude's knowledge and capabilities with new functions or custom commands (like "extract PDF forms")
• MCP: Connect external tools to Claude Code (like "access GitHub repositories")
• Plugins: Bundle all of the above together as complete customizations (marketplace packages)

Think of it this way: Skills and MCP add new capabilities. Hooks add automation. They're complementary, not overlapping.

"Will I encounter hook errors?"

Possibly, but they're usually non-blocking. If a hook fails:

• Claude Code continues working (hook errors don't stop your session)
• The error is logged, not shown as a blocker
• You can investigate later

Debugging hooks is advanced content (Part 5). For now, just know hook errors won't stop you from working.

"Should I enable hooks right now?"

Not necessary. Claude Code works perfectly fine without custom hooks. You can:

• Use Claude Code productively without any hooks
• Learn about hooks conceptually now
• Build hooks later when you're ready to optimize your workflow

No pressure to customize right now—focus on mastering basic workflows first.

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Try With AI

Open Claude Code and explore hooks conceptually with your AI companion.

Prompt 1: Understand Hooks

claude "Explain hooks in Claude Code. Give 2-3 useful examples where a hook would save time by automating a repetitive task."

Expected outcome: AI explains hooks as event-triggered automation and provides concrete examples (format code, run tests, load environment).

Prompt 2: Identify Opportunities

Think of a task you do repeatedly in your projects (running tests, formatting code, checking linting, deploying, loading configuration).

claude "I frequently [describe your repetitive task]. Could a Claude Code hook help automate this? If so, what would it do?"

Expected outcome: AI identifies how a hook could eliminate the repetitive step, discusses which event would trigger it, and explains the time savings.

Prompt 3: Future Learning Path

claude "Can I build custom hooks in Claude Code? How hard is it? When would I learn this? What are the prerequisites?"

Expected outcome: AI clarifies that hook building is intermediate-to-advanced content, explains prerequisites (Part 5), and positions hooks in the larger Claude Code customization landscape.