tool_use for Guaranteed Structure

You asked Claude for JSON and parsed the reply with json.loads(). It worked 95% of the time. The other 5%? A stray markdown fence, a trailing comma, a chatty preamble like "Here's the JSON you requested:" — and your pipeline throws.

For a Claude Certified Architect, that 5% is the whole problem. Production extraction, classification, and routing flows can't depend on the model happening to format text correctly. This lesson shows how tool_use plus a JSON Schema turns a probabilistic format into a guaranteed one — eliminating syntax errors and enforcing required fields.

A tool isn't only for taking actions. A tool definition is also a typed output contract. When you declare a tool with an input_schema, you're telling Claude exactly what shape its arguments must take — and the API validates the tool call against that schema.

So instead of asking for JSON in prose and hoping, you define a tool whose parameters are the structure you want, then force Claude to call it. The model fills in the fields; the schema guarantees the shape. Per the fact sheet: tool_use + JSON Schema eliminates syntax errors and enforces required fields.