With the constant evolution of AI-powered development tools, Claude Code has introduced a revolutionary feature: Hooks. This feature allows developers to customize and automate specific behaviors in the Claude Code lifecycle, transforming suggestions into executable code that works deterministically.
Hooks represent a qualitative leap in the customization of AI development tools, allowing each team and developer to adapt Claude Code to their specific needs and project standards.
What are Claude Code Hooks?
Claude Code Hooks are user-defined shell commands that execute automatically at various specific points in the Claude Code lifecycle. Unlike prompting instructions, hooks guarantee that certain actions always occur, providing deterministic control over the tool’s behavior.
The Problem They Solve
Traditionally, customizing AI tool behavior required:
- Repetitive instructions in every conversation
- Dependence on the LLM to remember and execute specific actions
- Inconsistencies in code standard application
- Manual processes for formatting, validation, and logging
Hooks eliminate these limitations by encoding rules as applications that execute automatically.
Transformative Use Cases
1. Automatic Code Formatting
# Hook that automatically formats TypeScript files
hook_command="if [[ \$file_path =~ \.ts$ ]]; then prettier --write \$file_path; fi"
2. Custom Notifications
# Slack notification when Claude requests permissions
hook_command="curl -X POST \$SLACK_WEBHOOK -d '{\"text\":\"Claude Code needs your attention\"}'"
3. Logging and Compliance
# Log all executed commands for auditing
hook_command="echo \$(date): \$command >> ~/.claude/audit.log"
4. Convention Validation
# Verify commits follow team standards
hook_command="./scripts/validate-commit-message.sh \$commit_message"
5. Custom Permissions
# Block modifications to production files
hook_command="if [[ \$file_path =~ ^production/ ]]; then exit 2; fi"
Step-by-Step Configuration
Basic Configuration: Logging Hook
Let’s create our first hook that logs all bash commands executed by Claude Code.
Step 1: Open Hooks Configuration
# In Claude Code, run the slash command
/hooks
Select the PreToolUse event to intercept commands before execution.
Step 2: Add Matcher
Matcher: Bash
This makes the hook only execute for shell commands.
Step 3: Configure the Hook
# Command that logs execution
echo "$(date): Command executed by Claude Code" >> ~/.claude/command_log.txt
Step 4: Save Configuration
Select User settings to apply the hook to all projects.
Advanced Configuration: Automatic Formatting
{
"hooks": {
"PostToolUse": [
{
"matcher": "Edit|Write",
"hooks": [
{
"type": "command",
"command": "if [[ \"$file_path\" =~ \\.(js|ts|jsx|tsx)$ ]]; then prettier --write \"$file_path\"; fi"
},
{
"type": "command",
"command": "if [[ \"$file_path\" =~ \\.go$ ]]; then gofmt -w \"$file_path\"; fi"
},
{
"type": "command",
"command": "if [[ \"$file_path\" =~ \\.py$ ]]; then black \"$file_path\"; fi"
}
]
}
]
}
}
Types of Hook Events
1. PreToolUse
Executes before Claude processes a tool.
Use cases:
- Permission validation
- Pre-condition verification
- Blocking dangerous operations
# Example: Block edits to critical files
if [[ "$file_path" =~ (package\.json|\.env) ]]; then
echo "Error: Critical file protected" >&2
exit 2 # Block the operation
fi
2. PostToolUse
Executes after a tool completes successfully.
Use cases:
- Automatic formatting
- Post-processing validation
- Change notifications
# Example: Run tests after code changes
if [[ "$file_path" =~ \.test\.(js|ts)$ ]]; then
npm test "$file_path"
fi
3. Notification
Executes when Claude Code sends notifications.
Use cases:
- Custom notifications
- Integration with external systems
- Multi-channel alerts
# Example: Discord notification
curl -H "Content-Type: application/json" \
-d '{"content":"Claude Code requires attention"}' \
"$DISCORD_WEBHOOK"
4. Stop
Executes when Claude Code finishes responding.
Use cases:
- Execute post-processing scripts
- Generate session reports
- Clean temporary files
# Example: Generate changes report
git diff --stat > session_changes.txt
Input Data Structure
Hooks receive contextual information via JSON in stdin:
PreToolUse Input
{
"event": "PreToolUse",
"session_id": "session_123",
"tool_name": "Edit",
"tool_input": {
"file_path": "src/component.tsx",
"content": "// New content...",
"start_line": 1,
"end_line": 10
}
}
PostToolUse Input
{
"event": "PostToolUse",
"session_id": "session_123",
"tool_name": "Bash",
"tool_input": {
"command": "npm test"
},
"tool_response": {
"exit_code": 0,
"stdout": "Tests passed",
"stderr": ""
}
}
Advanced Hook Examples
Code Validation System
#!/bin/bash
# validate_code.sh - Comprehensive validation hook
# Read input JSON
input=$(cat)
file_path=$(echo "$input" | jq -r '.tool_input.file_path // empty')
tool_name=$(echo "$input" | jq -r '.tool_name')
# Only process file operations
if [[ "$tool_name" != "Edit" && "$tool_name" != "Write" ]]; then
exit 0
fi
# Specific validations by file type
case "$file_path" in
*.js|*.ts|*.jsx|*.tsx)
# Validate JavaScript/TypeScript syntax
if ! npx tsc --noEmit "$file_path" 2>/dev/null; then
echo "Error: Invalid TypeScript code" >&2
exit 2
fi
# Run ESLint
if ! npx eslint "$file_path" --fix; then
echo "Warning: Linting problems detected" >&2
fi
;;
*.py)
# Validate Python syntax
if ! python -m py_compile "$file_path"; then
echo "Error: Invalid Python syntax" >&2
exit 2
fi
# Format with black
black "$file_path"
;;
*.go)
# Validate Go syntax
if ! go fmt -e "$file_path"; then
echo "Error: Invalid Go syntax" >&2
exit 2
fi
# Run go vet
go vet "$file_path"
;;
esac
echo "Validation completed for $file_path"
Security Best Practices
⚠️ Critical Considerations
Hooks execute commands with full user permissions without confirmation. This requires strict precautions:
1. Input Validation and Sanitization
#!/bin/bash
# secure_hook_template.sh
# Function to sanitize inputs
sanitize_input() {
local input="$1"
# Remove dangerous characters
echo "$input" | sed 's/[;&|`$(){}[\]\\]//g'
}
# Function to validate paths
validate_path() {
local path="$1"
# Block path traversal
if [[ "$path" == *".."* ]]; then
echo "Error: Path traversal detected" >&2
exit 1
fi
# Ensure path is within project
if [[ ! "$path" =~ ^[./] ]]; then
echo "Error: Path outside project" >&2
exit 1
fi
}
# Read and validate input
input=$(cat)
file_path=$(echo "$input" | jq -r '.tool_input.file_path // empty')
if [[ -n "$file_path" ]]; then
validate_path "$file_path"
file_path=$(sanitize_input "$file_path")
fi
2. Safe Use of Variables
# ❌ INCORRECT - Vulnerable to injection
command="ls $user_input"
# ✅ CORRECT - Properly quoted variables
command="ls \"$user_input\""
# ✅ SAFER - Prior validation
if [[ "$user_input" =~ ^[a-zA-Z0-9._/-]+$ ]]; then
command="ls \"$user_input\""
else
echo "Invalid input" >&2
exit 1
fi
Conclusion: Transforming Development with AI
Claude Code Hooks represent a fundamental paradigm in how AI tools integrate into real development workflows. By enabling deterministic automation and granular customization, they transform Claude Code from an assistance tool to an extensible development platform.
Key benefits:
- ✅ Guaranteed consistency in code standards
- ✅ Automation of repetitive tasks
- ✅ Deep integration with existing tools
- ✅ Granular control over AI behaviors
- ✅ Enterprise scalability with centralized policies
To get started:
- Identify repetitive manual processes in your workflow
- Implement simple hooks (logging, formatting)
- Gradually add more sophisticated validations and controls
- Share successful configurations with your team
Hooks not only improve individual productivity, but allow teams to encode their collective knowledge in automations that benefit the entire organization.
The future of software development lies in tools that not only assist, but adapt and evolve with the specific needs of each project and team. Claude Code Hooks marks the path toward that reality.
Useful links:
Tags: #ClaudeCode #Hooks #AI #Automation #DevOps #Workflow #Development #Productivity