https://github.com/1rgs/jsonformer
or
https://github.com/newhouseb/clownfish
or
https://github.com/mkuchnik/relm
or
https://github.com/ggerganov/llama.cpp/pull/1773
or
https://github.com/Shopify/torch-grammar
Overall there are a ton of these logit based guidance systems, the reason they don't get tons of traction is the SOTA models are behind REST APIs that don't enable this fine-grained approach.
Those models perform so much better that people generally settle for just re-requesting until they get the correct format (and with GPT-4 that ends up being a fairly rare occurrence in my experience)