Claude Code Hooks

---
name: claude-code-hooks
description: "Claude Code hook system for pre/post tool execution. Triggers on: hooks, PreToolUse, PostToolUse, hook script, tool validation, audit logging."
compatibility: "Claude Code CLI with settings.json support"
allowed-tools: "Bash Read Write"
depends-on: []
related-skills: [claude-code-debug, claude-code-headless]
---

# 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`:

```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

```bash
#!/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

```bash
# 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