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HomeDocsClaude Code CLI 10 Nov 2026
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Intercept and control agent behavior with hooks changedagent-sdk/hooks

Nearest release: v2.1.322, published 3 hours before upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Upstream edited this page at 10 Nov 2026 05:35 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 10 Nov 2026 05:37 UTC.

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243243* **Top-level fields** are accepted on every event: `systemMessage` shows a message to the user, and `continue` (`continue_` in Python) determines whether the agent keeps running after this hook. Some events discard them or deliver them elsewhere. Each [event's section](https://code.claude.com/docs/en/hooks.md#hook-events) on the hooks page says where they land.
244244* **`hookSpecificOutput`** controls the current operation. The fields you set inside depend on the hook event type:
245245 * For `PreToolUse` hooks, this is where you set `permissionDecision` (`"allow"`, `"deny"`, `"ask"`, or `"defer"`), `permissionDecisionReason`, and `updatedInput`. If you return `"defer"`, the turn ends with a result message whose `stop_reason` is `"tool_deferred"`, so you can [resume the call later](https://code.claude.com/docs/en/hooks.md#defer-a-tool-call-for-later).
246 * For `PostToolUse` hooks, you can set `additionalContext` to append information to the tool result. To replace the tool's output before Claude sees it, set `updatedToolOutput`, which works for any tool in both SDKs. The older `updatedMCPToolOutput` field replaces MCP tool output only.
246 * For `PostToolUse` hooks, you can set `additionalContext` to append information to the tool result. To replace the tool's output before Claude sees it, set `updatedToolOutput`, which works for built-in and MCP tools in both SDKs. The older `updatedMCPToolOutput` field replaces MCP tool output only.
247247 * In the TypeScript SDK, a `PostToolUse` callback can also return `classifierContext`, a short note about the tool call's result for the [auto mode](https://code.claude.com/docs/en/permission-modes.md#eliminate-prompts-with-auto-mode) permission classifier. Because your callback runs in your application's own process, the classifier may weigh a user statement you relay in the note as user intent. The field requires TypeScript Agent SDK v0.3.236 or later. [Annotate a result for the auto mode classifier](https://code.claude.com/docs/en/hooks.md#annotate-a-result-for-the-auto-mode-classifier) covers the length cap, the synchronous-only rule, and what not to put in the note.
248248 
249249Return `{}` to allow the operation without changes. SDK callback hooks use the same JSON output format as [Claude Code shell command hooks](https://code.claude.com/docs/en/hooks.md#json-output), which documents every field and event-specific option. For the SDK type definitions, see the [TypeScript](https://code.claude.com/docs/en/agent-sdk/typescript.md#synchookjsonoutput) and [Python](https://code.claude.com/docs/en/agent-sdk/python.md#synchookjsonoutput) SDK references.
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