Claude Code has been revolutionizing how we interact with source code, but what if we could make it even smarter and more autonomous? The answer lies in Claude Code Hooks – a powerful feature that allows you to customize and extend Claude Code’s behavior by executing shell commands at specific points in its lifecycle.
In this blog post, we’ll explore Claude Code Hooks, understand how they work, and provide some practical ideas to make the most of this feature.
1. What are Claude Code Hooks and What Can We Do With Them?
Claude Code Hooks are essentially user-defined shell commands that automatically execute at various “trigger points” (hook events) during Claude Code’s operation. This provides deterministic control over Claude Code’s behavior, ensuring that certain actions are always performed without relying on the choices of the large language model (LLM).
You can configure hooks in Claude Code’s settings files (~/.claude/settings.json
, .claude/settings.json
, or .claude/settings.local.json
).
The main types of hook events include:
- UserPromptSubmit: Triggers immediately when a user submits a prompt (before Claude processes it). This is excellent for prompt validation, adding context, or security filtering.
- PreToolUse: Runs before any tool is used (e.g., Edit, Bash, Git). This is a critical control point to block dangerous commands, enforce formatting rules, or check permissions.
- PostToolUse: Activates after a tool successfully completes its operation. Useful for analyzing results, logging commands, automating code formatting, or running tests.
- Notification: Runs when Claude Code sends a notification (e.g., when waiting for input or requesting permission). Can be used to create custom notifications (Slack, sound).
- Stop: Triggers when Claude Code finishes its response. Used for performing final checks or generating reports.
- SubagentStop: Triggers when a sub-agent’s task completes.
2. Experimenting and Understanding How Claude Code Hooks Work
To better understand, let’s consider a simple example: automatically formatting code after each time Claude edits a file.
Step 1: Open the Hooks Configuration In Claude Code, type /hooks
to open the configuration interface.
Step 2: Select the PostToolUse Hook Event We want the hook to run after Claude edits afile, so select PostToolUse.
Step 3: Add a Matcher Select + Add new matcher… and enter Edit|MultiEdit|Write
. This will ensure the hook only runs when Claude uses editing or file-writing tools.
Step 4: Add a Hook Command Select + Add new hook and enter the following command (example for a TypeScript file):
Bash
jq -r '.tool_input.file_path' | { read file_path; if echo \"$file_path\" | grep -q '\\.ts$'; then npx prettier --write \"$file_path\"; fi; }
This command will extract the edited file path, check if it’s a .ts
file, and then run npx prettier --write
to format it.
Step 5: Save the Configuration Select Project settings to apply this hook your projects.
Step 6: Test the Hook Ask Claude to edit a TypeScript file, and you’ll see Prettier automatically format the code once the edit is complete. If the hooks are not triggering as expected, try restarting Claude. Restarting usually helps the system recognize and apply the new configuration settings.Below is a demo video showing how it works:
3. Practical Ideas for Claude Code Hooks
The possibilities with Claude Code Hooks are endless. Here are some practical ideas to integrate this feature into your workflow:
Code Quality Enforcement:
- Automated Linting and Formatting: As in the example above, run Prettier, ESLint, Black, Ruff, gofmt, etc., after every file edit. This ensures code consistency throughout the project.
- Type Checking: Automatically run TypeScript, MyPy, or other type-checking tools after file edits to catch errors early.
- Custom Coding Rules: Enforce team- or project-specific coding rules by running custom scripts to check structure, naming conventions, or design patterns.
Automated Testing:
- Run Unit Tests: Automatically run unit tests (e.g., pytest, jest) after Claude edits files in
src/
ortests/
directories. - Lightweight Integration/E2E Tests: For minor changes, a subset of integration tests can be triggered to ensure no regressions.
- Run Unit Tests: Automatically run unit tests (e.g., pytest, jest) after Claude edits files in
Optimization and Security:
- Prevent Dangerous Commands: Use a PreToolUse hook to block dangerous shell commands like
rm -rf
or access to sensitive files (.env
). - Pre-commit Checks: Similar to Git hooks, run quality checks (e.g., searching for API keys, security checks) before Claude is allowed to execute
git_commit
. - Code Optimization: Run static analysis tools to suggest or enforce performance optimizations.
- Prevent Dangerous Commands: Use a PreToolUse hook to block dangerous shell commands like
Notifications and Logging:
- Custom Notifications: Send notifications to Slack, Discord, or use desktop notification tools (e.g., ntfy) when Claude needs your attention, completes a long task, or encounters an error.
- Command Logging: Log all commands Claude executes for tracking, debugging, or auditing purposes.
- Progress Tracking: Update progress status to a file or database to monitor long-running tasks.
Workflow Management:
- Automated Report Generation: After a major task is completed, automatically generate a report summarizing changes or outcomes.
- Documentation Updates: If Claude edits specific parts of the code, a hook can trigger automatic updates of related documentation sections.
- Flow Control: UserPromptSubmit and PreToolUse hooks can block actions if conditions are not met, forcing Claude to rethink or ask you for more information.
4. Conclusion
Claude Code Hooks transform Claude Code from a powerful coding assistant into a comprehensive and deterministic development partner. By defining simple yet powerful rules, you can automate mundane but crucial parts of your work, freeing up time and energy to focus on the more creative and complex aspects of software engineering.
Start experimenting with Claude Code Hooks today and discover how they can revolutionize your development process, leading to greater efficiency and better code quality!