ock |
| PostToolUse | Tool name | Run after successful tool |
| PostToolUseFailure | Tool name | Run after tool fails |
| Notification | Notification type | Run on notifications |
| Stop | - | Run when Claude stops (including clear, resume, compact) |
| PreCompact | "manual"/"auto" | Before compaction |
| UserPromptSubmit | - | When user submits |
| SessionStart | - | When session starts |

**Common tool matchers:** `Bash`, `Write`, `Edit`, `Read`, `Glob`, `Grep`

### Hook Types

**1. Command Hook** - Runs a shell command:
```json
{ "type": "command", "command": "prettier --write $FILE", "timeout": 30 }
```

**2. Prompt Hook** - Evaluates a condition with LLM:
```json
{ "type": "prompt", "prompt": "Is this safe? $ARGUMENTS" }
```
Only available for tool events: PreToolUse, PostToolUse, PermissionRequest.

**3. Agent Hook** - Runs an agent with tools:
```json
{ "type": "agent", "prompt": "Verify tests pass: $ARGUMENTS" }
```
Only available for tool events: PreToolUse, PostToolUse, PermissionRequest.

### Hook Input (stdin JSON)
```json
{
  "session_id": "abc123",
  "tool_name": "Write",
  "tool_input": { "file_path": "/path/to/file.txt", "content": "..." },
  "tool_response": { "success": true }  // PostToolUse only
}
```

### Hook JSON Output

Hooks can return JSON to control behavior:

```json
{
  "systemMessage": "Warning shown to user in UI",
  "continue": false,
  "stopReason": "Message shown when blocking",
  "suppressOutput": false,
  "decision": "block",
  "reason": "Explanation for decision",
  "hookSpecificOutput": {
    "hookEventName": "PostToolUse",
    "additionalContext": "Context injected back to model"
  }
}
```

**Fields:**
- `systemMessage` - Display a message to the user (all hooks)
- `continue` - Set to `false` to block/stop (default: true)
- `stopReason` - Message shown when `continue` is false
- `suppressOutput` - Hide stdout from transcript (default: false)
- `decision` - "block" for PostToolUse/Stop/UserPromptSubmit hooks (deprecated for PreToolUse, use hookSpecificOutput.permissionDecision instead)
- `reason` - Explanation for decision
- `hookSpecificOutput` - Event-specific output (must include `hookEventName`):
  - `additionalContext` - Text injected into model context
  - `permissionDecision` - "allow", "deny", or "ask" (PreToolUse only)
  - `permissionDecisionReason` - Reason for the permission decision (PreToolUse only)
  - `updatedInput` - Modified tool input (PreToolUse only)

### Common Patterns

**Auto-format after writes:**
```json
{
  "hooks": {
    "PostToolUse": [{
      "matcher": "Write|Edit",
      "hooks": [{
        "type": "command",
        "command": "jq -r '.tool_response.filePath // .tool_input.file_path' | xargs prettier --write 2>/dev/null || true"
      }]
    }]
  }
}
```

**Log all bash commands:**
```json
{
  "hooks": {
    "PreToolUse": [{
      "matcher": "Bash",
      "hooks": [{
        "type": "command",
        "command": "jq -r '.tool_input.command' >> ~/.claude/bash-log.txt"
      }]
    }]
  }
}
```

**Stop hook that displays message to user:**

Command must output JSON with `systemMessage` field:
```bash
# Example command that outputs: {"systemMessage": "Session complete!"}
echo '{"systemMessage": "Session complete!"}'
```

**Run tests after code changes:**
```json
{
  "hooks": {
    "PostToolUse": [{
      "matcher": "Write|Edit",
      "hooks": [{
        "type": "command",
        "command": "jq -r '.tool_input.file_path // .tool_response.filePath' | grep -E '\\.(ts|js)$' && npm test || true"
      }]
    }]
  }
}
```