Outlines is a Python library that constrains LLM outputs to match a specified structure during generation, addressing unpredictable outputs by passing a desired output type such as a JSON schema, regex, or grammar.
Project overview
The library shifts structured output enforcement from post-generation parsing to generation-time guarantees, and allows developers to switch between models like OpenAI and Gemini without changing application code.
Project type
Infrastructure · Prompt Engineering
Deployment
Refer to project documentation
License
Apache-2.0
Best for
Developers and AI engineers building Python applications who need to enforce structural constraints on text generation across different model providers.
README: LLMs are powerful but their outputs are unpredictable. Most solutions attempt to fix bad outputs after generation using parsing, regex, or fragile code that breaks easily.
README: Outlines guarantees structured outputs during generation — directly from any LLM.
README: Trusted by NVIDIA, Cohere, HuggingFace, vLLM, etc.