Grammars work best when aligned with prompt. That is, if your prompt gives you the right format of answer 80% of the time, the grammar will take you to a 100%.

Grammars work best when aligned with prompt. That is, if your prompt gives you the right format of answer 80% of the time, the grammar will take you to a 100%. If it gives you the right answer 1% of the time, the grammar will give you syntactically correct garbage.