@modelcontextprotocol/sdk
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    Interface CallToolResult

    The server's response to a tool call.

    interface CallToolResult {
        _meta?: { [key: string]: unknown };
        content: ContentBlock[];
        isError?: boolean;
        structuredContent?: { [key: string]: unknown };
        [key: string]: unknown;
    }

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    • [key: string]: unknown
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    _meta? content isError? structuredContent?

    Properties

    Optional_meta

    _meta?: { [key: string]: unknown }

    See General fields: _meta for notes on _meta usage.

    content

    content: ContentBlock[]

    A list of content objects that represent the unstructured result of the tool call.

    isError?: boolean

    Whether the tool call ended in an error.

    If not set, this is assumed to be false (the call was successful).

    Any errors that originate from the tool SHOULD be reported inside the result object, with isError set to true, not as an MCP protocol-level error response. Otherwise, the LLM would not be able to see that an error occurred and self-correct.

    However, any errors in finding the tool, an error indicating that the server does not support tool calls, or any other exceptional conditions, should be reported as an MCP error response.

    structuredContent?: { [key: string]: unknown }

    An optional JSON object that represents the structured result of the tool call.

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