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Instructor

Structured outputs from language models using Python type hints

4.7(202 reviews)freeFounded 2026
free tieropen sourceapi access

Instructor is a Python library that ensures LLM responses conform to specified data structures using Pydantic models. It adds validation, retries, and type safety to API calls with minimal code changes.

Instructor intercepts LLM API calls and enforces structured outputs by wrapping provider SDKs. It supports OpenAI, Anthropic, Cohere, and local models. Features include automatic retries on validation failures, streaming support, partial responses, and detailed error feedback. Reduces boilerplate for extracting typed data from unstructured LLM outputs.

Pros

  • Define output schemas as Python types—no custom prompting syntax required
  • Automatically retry failed validations without manual error handling
  • Works with multiple LLM providers through a unified interface
  • Stream responses while maintaining type guarantees
  • Minimal overhead—wraps existing client code with ~3 lines

Cons

  • Adds latency for validation and potential retries on complex schemas
  • Performance depends on model compliance—some models struggle with strict constraints
  • Limited to Python ecosystem; no native support for other languages

Best For

Python developers building production systems that need reliable, typed data extraction from LLM outputs without manual JSON parsing and validation.

Pricing

Free Forever

Free
  • Core features
  • Email support

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