Agent-Based Hooks - Claude Code
Spawn subagents to handle complex hook logic.
Agent-based hooks spawn a subagent to handle the hook, giving you full tool access and multi-step reasoning inside a hook.
What it does
When the event fires, Claude Code hands off to a subagent with its own tools, context, and system prompt. The subagent can read files, run commands, consult external APIs, and return a decision. This is overkill for logging but perfect for rich policy - "review this diff for security issues before allowing the write".
When to use it
- Policies that need to read multiple files before deciding.
- Advisory reviewers that post comments rather than block.
- Complex approval flows that can't fit in a single prompt.
- Integrating an auditor role into the hook pipeline.
Gotchas
- Agents in hooks are slow relative to command or prompt hooks. Use sparingly.
- Each hook fire costs a subagent spawn. Cache where possible.
- Circular dependencies (hook agent triggers same hook) are easy to write and hard to debug.
Official docs: https://code.claude.com/docs/en/hooks.md#agent-based-hooks
Technical content at the intersection of AI and development. Building with AI agents, Claude Code, and modern dev tools - then showing you exactly how it works.
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