Outlines
Structured text generation with schema and regex constraints
Outlines is profiled here as a Prompt Engineering tool for engineering teams. Read about features, pricing, and how it compares to related options in the tools directory.
Description
Outlines is an open-source library from the dottxt team that makes language models produce structured output reliably. Developers describe the shape they want as a JSON schema, regular expression, or context-free grammar, and Outlines steers token sampling so the generated text always conforms. The library works as a thin layer over open models and inference servers, which lets teams enforce data contracts on model output without changing their serving stack. The dottxt team maintains Outlines as open source, and its constraint logic adds little overhead because it compiles the schema into an efficient state machine.
Key Capabilities:
JSON schema enforcement that returns objects matching a defined structure
Regular expression constraints that pin output to an exact pattern
Context-free grammars for generating syntactically valid code or DSLs
Structured sampling that runs efficiently over open models
Integration with vLLM, Transformers, and other inference backends
Multiple-choice and typed generation for classification-style tasks
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