Guidance

Guidance is an open-source Python library for steering large language model output through native Python control flow rather than brittle prompt engineering. Instead of composing free-form prompts, you write loops, conditionals, tool use, and generation directly in code with a Pythonic API, letting you guarantee structured output such as JSON, code, or multiple-choice answers. Launched in 2022, Guidance was among the first frameworks to make constrained generation practical, reducing latency and cost versus conventional prompting or fine-tuning. It remains a valuable educational tool and a solid foundation for understanding grammar-based decoding, even though the original repository was archived in late 2023 and no longer receives updates. The core interface is centered on a few primitives: `gen()` generates text with optional `regex` constraints to enforce any regular expression, while `select()` forces the model to pick from a predefined list—ideal for A/B/C/D questions or fixed taxonomies. The `@guidance` decorator lets you build reusable prompt functions, like a `zero_shot_multiple_choice` helper that automatically formats questions and enforces a valid selection. You can also capture generated text into named variables and reference them later, making complex multi-step workflows straightforward. Development is well supported. The `Mock` model lets you validate grammars offline without making any model API calls, and the Jupyter notebook widget gives an interactive view of the generation process. Model objects are immutable, simplifying debugging and experimentation. The library supports several backends—Transformers, llama.cpp, and OpenAI—and is distributed under the MIT license via PyPI. Guidance's main limitation is its maintenance status: the repository was archived on October 22, 2023, meaning no new features or bug fixes. For teams starting fresh production work, actively maintained alternatives like Outlines or LMQL are safer bets. But for learning