PRODUCTION SCENARIO
Quarrystone's search backend accepts a proprietary filter language such as region:eu AND (price<40 OR tier:basic), with nested groups, which is plain text rather than JSON. A function tool with a single string parameter produces syntactically invalid filters about one call in twelve.
Which tool design constrains the model's output to the filter language?
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Show answer and explanation
Answer: Define a custom tool with a Lark grammar format describing the whole filter language
Custom tools let the model emit an arbitrary string, and a Lark grammar is context-free, so it can express the balanced nested groups the filter language allows. A regex grammar also constrains the string but cannot match nested parentheses, a schema description is guidance the model can miss, and strict JSON validation checks the object's shape while the filter text inside a string property goes unparsed.
Official Source: https://developers.openai.com/api/docs/guides/function-calling ↗