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HomeDocsClaude Code CLI 10 Oct 2026
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Agent SDK reference - TypeScript changedagent-sdk/typescript

Upstream edited this page at 10 Oct 2026 18:15 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 Oct 2026 18:37 UTC.

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15361536* A WebFetch or WebSearch call that Claude Code moved to the background to deliver a `'now'` message: the user message carrying that call's `tool_result` has `tool_use_result` set to `{ detachedToolCall: true }`. The call is still running, and Claude receives its result once it finishes. No second `tool_result` for that `tool_use_id` follows, so if your application draws a row for each tool call, mark this row as moved to the background when this message arrives. Requires Claude Code v2.1.287 or later.
15371537* An MCP tool whose result contains `resource_link` blocks: `tool_use_result` is an object with a `resourceLinks` array of [`SDKMcpResourceLink`](#sdkmcpresourcelink) entries. Claude receives each link as a line of text in the `tool_result` block, so read `resourceLinks` to render the files the server returned instead of parsing that text. Claude Code omits `resourceLinks` when the result has no links and on results from subagents, keeps at most 50 links per result, and stops adding links once the array reaches 64 KiB of serialized JSON. `resourceLinks` requires Agent SDK v0.3.257 or later.
15381538* An MCP tool that returns [`structuredContent`](#calltoolresult): `tool_use_result` is an object whose `structuredContent` member holds what the server sent and whose `content` member holds the [`McpOutput`](#mcpoutput) value. Results from subagents don't carry `structuredContent`.
1539* An MCP tool whose `structuredContent` serializes to more than 1,048,576 characters of JSON: Claude Code leaves `structuredContent` off `tool_use_result` and sets `structuredContentOmitted: true` in its place, so your application can tell a dropped object from a tool that sent none. The other members, such as `content` and `resourceLinks`, stay, and what Claude receives doesn't change. Tools from [in-process SDK servers](/docs/en/agent-sdk/custom-tools) and tools whose `tools/list` entry declares an [MCP Apps `_meta.ui` resource](#mcpserverstatus) are exempt and deliver the object whole. Claude Code v2.1.287 or later applies this cap.
1539* An MCP tool whose `structuredContent` serializes to more than 1,048,576 characters of JSON: Claude Code leaves `structuredContent` off `tool_use_result` and sets `structuredContentOmitted: true` in its place, so your application can tell a dropped object from a tool that sent none. The other members, such as `content` and `resourceLinks`, stay, and what Claude receives doesn't change. Claude Code v2.1.287 or later applies this cap. Two kinds of tool differ:
1540 * Tools from [in-process SDK servers](/docs/en/agent-sdk/custom-tools) are exempt and deliver the object whole.
1541 * A tool whose `tools/list` entry declares an [MCP Apps `ui://` resource](#mcpserverstatus) has a limit of 8,388,608 characters on Claude Code v2.1.295 or later, and versions before v2.1.295 exempt it.
15401542 
15411543### `SDKUserMessageReplay`
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53145316 hook_id: string;
53155317 hook_name: string;
53165318 hook_event: string;
5317 output: string;
5318 stdout: string;
5319 stderr: string;
5320 exit_code?: number;
5321 outcome: "success" | "error" | "cancelled";
5322 uuid: UUID;
5323 ses
5319 o
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