hook-development

Hooks enable event-driven automation in Claude Code plugins for validation, context, and policy enforcement.

• Event-driven scripts that respond to specific actions like tool use or session start
• Used to validate, modify, or block operations based on context or policy
• Supports prompt-based (LLM) and command-based (bash) execution
• Can enforce safety, completeness, and context loading across workflows

• Validate tool use before execution (PreToolUse)
• React to tool results (PostToolUse)
• Enforce completion standards (Stop, SubagentStop)
• Load project context at session start (SessionStart)
• Support prompt-based decisions with natural language reasoning
• Allow deterministic checks via bash commands
• Can modify inputs, decisions, or system context
• Output includes decisions, system messages, and suppression flags

1. 1.Identify the event (PreToolUse, Stop, etc.) to hook into
2. 2.Choose prompt-based for context-aware decisions or command-based for deterministic checks
3. 3.Structure hooks in hooks.json (plugin format) or settings.json (user format)
4. 4.Define matcher rules and hook actions (prompt/command) for specific events
5. 5.Ensure correct output format with decision, systemMessage, and exit codes