When defining a tool for Claude tool use, which element is REQUIRED so Claude can call the tool correctly?
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Short Explanation and Infographic
Tool use needs a clear contract: name, description, and a JSON Schema for inputs so Claude knows exactly what arguments to pass.
Full explanation below image
Full Explanation
Claude tool use requires each tool definition to include a unique name, human-readable description, and input_schema (JSON Schema) describing parameters. Claude then emits structured tool_use blocks with arguments matching that schema. Description-only is insufficient for reliable structured calls. OpenAPI upload and Console decorators are not the standard API contract for Messages tool use.