# Practical ways to use the Claude Agent SDK 🪝 Intercept every agent action with hooks for auditing, control, and notifications. Hooks execute custom code at lifecycle events like `PreToolUse`, `PostToolUse`, `Stop`, and `Notification` to validate, log, block, or transform agent behavior. 📌 Title: Intercepting and Controlling Agent Behavior with Hooks 🔗 URL: 🧩 Overview Hooks are SDK callbacks that fire before/after tool execution, on stop, notifications, etc. `HookMatcher` targets specific tools by pattern. `permissionDecision` controls allow/deny. Hooks run outside the context window — zero token cost. 🛠 How to use it In the `hooks` option, use event names (`PreToolUse` / `PostToolUse` / `Notification` etc.) as keys with `HookMatcher` specifying matcher patterns (`"Edit|Write"`, `"^mcp__"` etc.) and callback functions. Callbacks return `permissionDecision` (`allow` / `deny`) or `updatedInput` to control tool execution. 🏗 Practical usage - Block `.env` writes or `/etc` operations in `PreToolUse` with `deny`, injecting a `systemMessage` to explain why to Claude. - Log all file changes in `PostToolUse` to an audit file for compliance. - Rewrite Write's `file_path` in `PreToolUse` to redirect all writes to `/sandbox` (`updatedInput` + `allow`). - Forward permission requests and idle states to Slack or PagerDuty via `Notification` hooks. 💡 Use cases 🛡 Automatic blocking of dangerous operations 📝 Audit logging of all file changes 📨 Event forwarding to external notification services 🔀 Sandbox redirection for write operations ⚠️ Watch out Multiple hooks run in parallel with priority: `deny > defer > ask > allow`. Use `async_: True` for non-blocking async processing. `SessionStart` / `SessionEnd` are TypeScript only. #ClaudeAgentSDK# #AI#