Every Structured Outputs comparison and buyer's guide for building AI agents — 2 pieces and counting. Each is a head-to-head or a “best X for Y” roundup with a sources-backed verdict.
Forcing a model to emit valid JSON is a solved problem. Doing it without slowing generation to a crawl is the one that produced three new engines — and your serving stack probably already picked one for you.
Three libraries promise the same thing — reliable JSON from a language model — and disagree completely on where to enforce it. The right pick follows one question: do you control the decoder?