A schema-defined tool provides a structured interface between Claude and the application. The tool’s input_schema can declare required properties, nested work-experience and education objects, arrays of skills, and exact data types. Claude then supplies the extracted resume information as tool-call arguments, which the application can read directly from the tool_use response.

Anthropic’s tool documentation specifies that a custom tool definition includes a JSON Schema object describing its expected parameters. Current strict tool use can additionally enforce that generated tool arguments match the declared schema exactly. This removes the need to locate JSON inside free-form text or depend on post-generation repair. ( https://docs.anthropic.com/en/docs/agents-and-tools/tool-use/implement-tool-use )

Option A is fragile because regular expressions do not provide a robust parser for arbitrary nested JSON and cannot correct missing properties or incorrect types. Option B improves formatting behavior but remains probabilistic. Option C doubles latency and creates two opportunities for information loss: first during extraction and again during reformatting.

In a production design, fields that may genuinely be absent from a resume should be optional or nullable rather than forcing invented values. The tool schema should also use strict: true where supported. Among the available choices, D provides the strongest structural guarantee and the cleanest downstream integration.

Official references/topics: Tool Use Responses, Input Schemas, Strict Tool Use, Nested Structured Extraction.