hook-authoring

## When NOT To Use - Auditing a hook that already exists (use `abstract:hooks-eval`) - Choosing where a hook should live (use `abstract:hook-scope-guide`) - Authoring a skill rather than a hook (use `abstract:skill-authoring`) # Hook Authoring Guide ## Overview Hooks are event interceptors that allow you to extend Claude Code and Claude Agent SDK behavior by executing custom logic at specific points in the agent lifecycle. They enable validation before tool use, logging after actions, context injection, workflow automation, and security enforcement. This skill teaches you how to write effective, secure, and performant hooks for both declarative JSON (Claude Code) and programmatic Python (Claude Agent SDK) use cases. ### Key Capabilities - **PreToolUse**: Validate, filter, or transform tool inputs before execution; inject context (2.1.9+) - **PostToolUse**: Log, analyze, or modify tool outputs after execution - **UserPromptSubmit**: Inject context or filter user messages before processing - **Stop/SubagentStop**: Cleanup, final reporting, or result aggregation - **TeammateIdle/TaskCompleted**: Multi-agent coordination and orchestration (2.1.33+) - **PreCompact**: State preservation before context window compaction > **New in 2.1.9**: PreToolUse hooks can now return `additionalContext` to inject information before a tool executes. This enables patterns like cache hints, security warnings, or relevant context injection. ## Quick Start ### Your First Hook (JSON - Claude...