A county animal-control office exposes a lookup_impound_record tool to Claude. Its input_schema defines the properties animal_id, shelter_site, and intake_date, and the description of animal_id reads "required - the tag number of the impounded animal." The required array in the schema is empty. In practice Claude sometimes calls the tool with no animal_id at all. What is the correct explanation of how a parameter is actually made mandatory?
Select an answer to reveal the explanation.
Short Explanation
The schema is the form and the description is the sticky note stuck to it. A note saying "do not forget this box" is advice; the required array is what marks the box mandatory.
Full Explanation
A tool's input_schema is a JSON Schema object, and JSON Schema deliberately separates two concerns. The properties object declares what each field is and what type it holds, while the sibling required array names the subset that must be present for the object to be valid. Only the required array carries structural obligation, so an empty one leaves animal_id optional no matter how its description is worded.
Listing animal_id in the required array is the mechanism that makes the parameter mandatory. It moves the constraint out of natural-language guidance and into the validated shape of the call, so a request arriving without the tag number is invalid rather than merely unhelpful. An architect wanting a hard guarantee also has the impound server itself reject such a call.
Rewriting the description more forcefully only changes guidance the model weighs, so an omitted argument stays reachable because nothing validates the call; property order is not significant in JSON Schema, so moving animal_id to the top of properties marks nothing as mandatory; and the tool name is only the identifier the model addresses, so renaming it to mention the argument does not define the argument contract.
Exam caveat: description text is not useless, because it is what tells Claude when the tool applies and what a good tag number looks like, so the fix is to add required and keep a clear description rather than trading one for the other. Operational check: add animal_id to required, replay prompts that previously omitted it, and confirm the call fails validation instead of reaching the impound database.