Outlines
Library from .txt for structured generation that guarantees LLM output matches a JSON schema, regex or grammar.
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Use cases
About Outlines
Outlines is listed in our frameworks category and is aimed at builders. Library from .txt for structured generation that guarantees LLM output matches a JSON schema, regex or grammar. Pricing, as the maker states it: Open source. Maturity: Mature. We last checked the official link on 2026-10-18.
What is Outlines?
Outlines is a library for structured outputs from LLMs, made by the team at .txt. It makes models generate output that follows a schema or format you define.
Its README lists examples such as customer-support triage, e-commerce product categorization and parsing event details. It is trusted by projects including NVIDIA, Cohere, Hugging Face and vLLM, according to its maker.
Sources: the official README and our directory listing, checked 2026-10-18. Official site: dottxt-ai.github.io/outlines.
Who is Outlines for?
Developers who need LLM output that reliably matches a JSON schema, type or grammar.
Outlines at a glance
- Open source: Yes (Apache License 2.0)
- GitHub: dottxt-ai/outlines · 15,962 stars (as of Oct 21, 2026)
Key features
- Structured generation that follows a schema
- JSON schemas, types and grammars
- Works with popular model backends
- Open source from .txt
Outlines FAQ
What is Outlines?
Outlines is a library for structured outputs from LLMs, made by the team at .txt. It makes models generate output that follows a schema or format you define.
Who is Outlines for?
Developers who need LLM output that reliably matches a JSON schema, type or grammar.
Is Outlines free?
Outlines's pricing, as the maker states it: Open source. Open-source tools are free to use, though you may still pay for model API usage or a hosted plan. Check the official site for current plans.
Is Outlines open source?
Yes. Outlines is released under the Apache License 2.0, according to its GitHub repository.
What are alternatives to Outlines?
Similar tools include Marvin, Instructor, BAML, Guidance, Mirascope and AgentFlow.
Outlines ratings and reviews
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Outlines alternatives
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Instructor
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BAML
Typed programming language for agents and LLM functions, with runtime types, typed errors and structured outputs designed to reduce agent mistakes.
Guidance
Programming paradigm for steering language models that constrains output with regex and grammars and interleaves control flow with generation.
Mirascope
Lightweight Python library for calling any LLM with typed outputs and tools through one interface, without a heavy framework.
AgentFlow
Stanford's trainable agentic system where planner, executor, verifier and generator modules coordinate, with a Hugging Face demo.
Related lists
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