Outlines
dottxt-ai.github.iolibraryself-hosted
Outlines is a self-hosted library in the Prompt Engineering layer of the AI stack. Constrained generation that masks the token space to valid output.
By Lattice editorial · Facts verified · method
- licence
- Apache-2.0
- language
- Python
- cost
- free
- owned by
- Applied Engineering
Verified 2026-09build refuses it from 2027-04
Use Outlines when
Token-level constrained generation from a JSON schema or grammar.
Skip Outlines when
Post-hoc validation is enough for your use case.
Makes the prompt an artifact you can diff and test. — that is what this layer of the stack is answerable for. See the full Prompt Engineering section for the rest of the options.
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[](https://lattice.kunjshah.in/prompt-engineering/outlines)Quick answers
- Is Outlines open source?
- Yes. Outlines is open source under the Apache-2.0 licence. It is free to use.
- What are the alternatives to Outlines?
- The closest alternatives to Outlines are Guidance and Instructor.
Compared in
Reading on prompts
- Prompt, or fine-tune?Almost every 'the model does not know this' problem is a retrieval problem wearing a hat. Here is how to tell the difference before you spend a week on a training run.
- Context is a budget, not a containerThe instinct is to keep everything in case it is needed. The models are not filing systems, and past a certain length the middle of your context is doing nothing but costing money.
Alternatives to Outlines
Listed as an alternative to
- InstructorInstructorSchema-constrained extraction with automatic validation and retry.Use when Schema-validated extraction with typed retry and partial streaming.Skip when You need a hard token-level guarantee rather than validation.MIT · self-hosted · free
- GuidanceGuidanceConstrained generation by interleaving control flow and model output.Use when Constrained decoding with control flow interleaved into generation.Skip when You need better ergonomics for plain extraction.MIT · self-hosted · free
Also in prompts
- DSPyDSPyDeclarative prompting that compiles to optimized programs from examples.Use when Compiling prompts into optimised programs from labelled examples.Skip when You have no examples and no way to score them.MIT · self-hosted · free
- InstructorInstructorSchema-constrained extraction with automatic validation and retry.Use when Schema-validated extraction with typed retry and partial streaming.Skip when You need a hard token-level guarantee rather than validation.MIT · self-hosted · free
- HumanloopHumanloopPrompt versioning and evaluation for production teams.Use when Prompt versioning and evaluation run by a product team.Skip when Prompts or data cannot be sent to a vendor.proprietary · saas · usage-based
- GuidanceGuidanceConstrained generation by interleaving control flow and model output.Use when Constrained decoding with control flow interleaved into generation.Skip when You need better ergonomics for plain extraction.MIT · self-hosted · free
- PromptLayerPromptLayerPrompt registry with request logging and regression testing.Use when A prompt registry with request logging and regression tests.Skip when You need self-hosting.proprietary · saas · usage-based
- AgentaAgentaOpen-source prompt management with a playground and versioning.Use when Open-source prompt management with a playground and versioning.Skip when You need eval depth rather than prompt ergonomics.Apache-2.0 · self-hosted · free-tier
- PromptwatchPromptwatchPrompt regression tests and side-by-side comparison.Use when Prompt regression tests and side-by-side comparison.Skip when You need self-hosting.proprietary · saas · usage-based
- TextGradTextGradAutomatic prompt optimisation via textual feedback loops.Use when Automatic prompt optimisation via textual feedback loops.Skip when Optimising without an eval set is guessing.MIT · self-hosted · free