tool_result

Tools

Definition

A content block type in the user message that returns the output of a tool execution back to Claude. Must include the 'tool_use_id' matching the original tool_use block. Can be text, images, or error messages. Claude processes the result and continues reasoning.

Example Usage

After executing a tool, append a user message with role='user' containing a tool_result block with the execution output.

Related Concepts

Tool Use Flow & Mechanics

Agentic Architecture

Tool use follows a define -> select -> execute -> return cycle

Structured Error Response Design

Tool Design & MCP

Use the MCP isError flag to distinguish tool failures from successful empty results

Related Terms

tool_use Content Block Agentic Loop

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