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.
Outlines guarantees structured outputs during generation — directly from any LLM.
- Works with any model - Same code runs across OpenAI, Ollama, vLLM, and more
- Simple integration - Just pass your desired output type:
model(prompt, output_type) - Guaranteed valid structure - No more parsing headaches or broken JSON
- Provider independence - Switch models without changing code
- Rich structure definition - Use Json Schema, regular expressions or context-free grammars
🚀 Building the future of structured generation
We're working with select partners to develop new interfaces to structured generation.
⚡ Try the Dottxt API
Want guaranteed structured generation without running your own models? The Dottxt API delivers 100% schema-compliant outputs via a simple REST API — no GPU, no setup.
🔍 Audit your schema
Share one schema and we show you what breaks under generation, the constraints that fix it, and compliance rates before and after. Need XML, FHIR, custom schemas or grammars? Let's talk.
See it in action
from pydantic import BaseModel
from typing import Literal
import outlines
import openai
class Customer(BaseModel):
name: str
urgency: Literal["high", "medium", "low"]
issue: str
client = openai.OpenAI()
model = outlines.from_openai(client, "gpt-4o")
customer = model(
"Alice needs help with login issues ASAP",
Customer
)
# ✓ Always returns valid Customer object
# ✓ No parsing, no errors, no retries
Quick install
Features
- Reliable - Guaranteed schema compliance -- always valid JSON.
- Feature-rich - Supports a large proportion of the JSON Schema spec, along with regex and context-free grammars.
- Fast - Microseconds of overhead vs seconds of retries. Compilation happens once, not every request.
- Simple - Outlines is a low-abstraction library. Write code the way you normally do with LLMs. No agent frameworks needed.
Supported inference APIs, libraries & servers
Who is using Outlines?
Hundreds of organisations and the main LLM serving frameworks (vLLM, TGI, LoRAX, xinference, SGLang) use Outlines. Prominent companies and organizations that use Outlines include:
Organizations are included either because they use Outlines as a dependency in a public repository, or because of direct communication between members of the Outlines team and employees at these organizations.
Still not convinced, read what people say about us. And make sure to take a look at what the community is building!
Outlines people
Outlines would not be what it is today without a community of dedicated developers:
About .txt
Outlines is built with ❤️ by .txt.
.txt solves the critical problem of reliable structured output generation for large language models. Our commercially-licensed libraries ensure 100% compliance with JSON Schema, regular expressions and context-free grammars while adding only microseconds of latency. Unlike open-source alternatives, we offer superior reliability, performance, and enterprise support.
Acknowledgements
Outlines was originally developed at @NormalComputing by @remilouf and @BrandonTWillard. It is now maintained by .txt.