Agent SDK Hooks: Quick Reference — Agentic Architecture & Orchestration (Claude Certified Architect)

Agent SDK Hooks — Quick Reference This quick reference provides essential facts and guidelines for using Agent SDK hooks within the Claude Agent SDK...

Agent SDK Hooks — Quick Reference

This quick reference provides essential facts and guidelines for using Agent SDK hooks within the Claude Agent SDK, a core component for designing and orchestrating agentic loops and multi-agent systems.

What Are Agent SDK Hooks?

Agent SDK hooks are programmable interception points in the agent lifecycle that enable developers to intercept, modify, or extend tool calls and workflow execution within agentic architectures.

Key Hook Types and Their Roles

Pre-Tool Call Hook: Executes before a tool or subagent is invoked. Used to validate inputs, modify parameters, or enforce preconditions.
Post-Tool Call Hook: Runs immediately after a tool call completes. Useful for processing outputs, logging, or triggering subsequent actions.
Error Handling Hook: Activated when a tool call or workflow step fails. Enables custom error recovery or fallback strategies.
Context Management Hook: Manages context passing between coordinator and subagents, ensuring relevant state is maintained or transformed appropriately.

Rules and Best Practices

Minimal Side Effects: Hooks should avoid unintended side effects that could disrupt the agentic loop's deterministic behavior.
Idempotency: Design hooks to be idempotent where possible, supporting safe retries and workflow resumption.
Performance Awareness: Keep hook logic efficient to prevent bottlenecks in multi-step workflows.
Clear Separation: Use hooks to separate cross-cutting concerns (e.g., logging, validation) from core agent logic.

Common Use Cases

Input Sanitization: Pre-tool call hooks can sanitize or enrich inputs before execution.
Output Transformation: Post-tool call hooks allow formatting or filtering outputs for downstream agents.
Dynamic Task Routing: Hooks can redirect tasks dynamically based on runtime conditions.
Context Forking and Resumption: Manage session state changes and branching workflows via context hooks.

Example Hook Implementation Pattern

Example: Pre-Tool Call Hook to Validate Inputs

Purpose: Ensure required parameters are present before tool execution.

Intercept the tool call request.
Check for mandatory fields in the input context.
If validation fails, raise an error or modify inputs.
Allow the tool call to proceed if validation passes.

Summary

Agent SDK hooks are vital for effective orchestration in Claude agentic architectures. They provide flexible control points for managing tool calls, context passing, error handling, and workflow enforcement. Mastery of these hooks supports robust, maintainable multi-agent systems with clear task decomposition and session management.

For detailed API references and implementation guides, consult the official Claude Agent SDK documentation.

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