Claude Code Hooks

Execute custom scripts before/after Claude Code tool invocations.

Quick Reference

Event	When	Has Matcher
`PreToolUse`	Before tool execution	Yes
`PostToolUse`	After tool completes	Yes
`PermissionRequest`	Permission dialog shown	Yes
`Notification`	Notifications sent	Yes
`UserPromptSubmit`	User submits prompt	No
`Stop`	Agent finishes	No
`SubagentStop`	Subagent finishes	No
`PreCompact`	Before context compaction	No
`SessionStart`	Session begins/resumes	No
`SessionEnd`	Session ends	No

Basic Configuration

Add to ~/.claude/settings.json or .claude/settings.local.json:

{
  "hooks": {
    "PreToolUse": [{
      "matcher": "Bash",
      "hooks": [{
        "type": "command",
        "command": "$CLAUDE_PROJECT_DIR/hooks/validate.sh",
        "timeout": 5000
      }]
    }]
  }
}

Matcher Patterns

Pattern	Matches
`"Write"`	Only Write tool
`"*"` or `""`	All tools
`"mcp__*"`	All MCP tools
`"Bash"`	Bash commands

Hook Script Requirements

#!/bin/bash
# Receives JSON via stdin: { "tool_name": "...", "tool_input": {...} }
INPUT=$(cat)
TOOL=$(echo "$INPUT" | jq -r '.tool_name')

# Exit codes:
# 0 = Success (continue)
# 2 = Block with error (stderr shown to Claude)
# Other = Non-blocking error

Common Use Cases

Use Case	Event	Example
Validate inputs	PreToolUse	Block dangerous commands
Audit logging	PostToolUse	Log all tool usage
Custom approval	PermissionRequest	Slack notification
Session init	SessionStart	Load project context

Security Checklist

Quote all variables: "$VAR" not $VAR
Validate paths (no .. traversal)
Use $CLAUDE_PROJECT_DIR for paths
Set reasonable timeouts
Handle jq parsing errors

Troubleshooting

# Debug hook loading
claude --debug

# List registered hooks
/hooks

# Test script manually
echo '{"tool_name":"Bash"}' | ./hooks/validate.sh

Official Documentation

https://code.claude.com/docs/en/hooks - Hooks reference
https://code.claude.com/docs/en/settings - Settings configuration

Additional Resources

./references/hook-events.md - All events with input/output schemas
./references/configuration.md - Advanced config patterns
./references/security-patterns.md - Production security

See Also: claude-code-debug for troubleshooting, claude-code-headless for CLI automation

claude-code-hooks