PRODUCTION SCENARIO
A set_alarm tool takes a unit parameter, typed in its input_schema as a plain string. In testing Claude sometimes sends secs or hr, and the server rejects the call.
Which change stops those invalid values at the source?
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Answer: Constrain the `unit` property with an `enum` of seconds, minutes, and hours.
Anthropic tool schemas are JSON Schema, so an enum on the property restricts the value to the listed literals, the way the documented get_weather tool restricts unit to celsius or fahrenheit. Strict tool use guarantees that inputs match the schema, but a schema that says only 'string' still admits secs, so strict alone changes nothing here. A description is guidance the model may or may not follow, not a constraint the API enforces. And normalising on the server hides the problem instead of stopping it, and breaks the moment a new abbreviation appears.