LMQL

LMQL is worth adding because it represents a different philosophy from plain prompt engineering libraries: language-model interaction becomes a query language with constraints, control flow, and declarative structure rather than a pile of strings in application code. The official docs and site position it as a language for scripted prompting, constraints, tool augmentation, and model-agnostic integration. That makes LMQL especially relevant for teams that want prompts and control logic to be explicit, composable, and inspectable rather than hidden inside application glue.

Its pricing posture is fully open-source at the language layer. There is no public software subscription fee on the official docs or site. The framework can run against local and hosted backends, so the real cost model depends on whichever inference providers or infrastructure the team connects beneath it. That is the honest editorial summary: LMQL is free as a language and runtime, but it does not erase model or compute cost.