If you want avoid startup cost, llguidance [0] has no compilation phase and by far the fullest JSON support [1] of any library. I did a PoC llama.cpp integration [2] though our focus is mostly server-side [3].

[0] https://github.com/guidance-ai/llguidance [1] https://github.com/guidance-ai/llguidance/blob/main/parser/s... [2] https://github.com/ggerganov/llama.cpp/pull/10224 [3] https://github.com/guidance-ai/llgtrt