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Langextract

Free

A Python library for extracting structured information from unstructured text using LLMs with precise source grounding and interactive visualization.

FreeFree tier
Inputs: text
Type
Open Source

About Langextract

LangExtract is a Python library that uses large language models (LLMs) to extract structured information from unstructured text documents based on user-defined instructions. It is designed to process materials such as clinical notes or reports, identifying and organizing key details while ensuring the extracted data corresponds precisely to the source text. Key capabilities include precise source grounding that maps extractions to their exact location, reliable structured outputs enforced via few-shot examples and controlled generation, optimization for long documents through chunking and parallel processing, interactive HTML visualization of extractions, and flexible support for both cloud-based LLMs (e.g., Google Gemini) and local models via Ollama. The library is open source under the Apache 2.0 license and requires Python 3.10 or later.

Key Features

Precise source grounding: maps every extraction to its exact location in source text for traceability and visual highlighting
Reliable structured outputs: enforces consistent output schema based on few-shot examples using controlled generation in supported models
Optimized for long documents: uses text chunking, parallel processing, and multiple passes to overcome the needle-in-a-haystack challenge
Interactive visualization: generates self-contained HTML files to review thousands of extracted entities in original context
Flexible LLM support: works with cloud-based models like Google Gemini and local open-source models via Ollama
Adaptable to any domain: define extraction tasks with just a few examples, no fine-tuning required
Leverages LLM world knowledge: uses precise prompt wording and few-shot examples to influence extraction accuracy

Pros & Cons

Pros
  • Open source and free to use under Apache 2.0 license
  • Precise source grounding enables verification and traceability of extractions
  • Handles long documents effectively through chunking and parallel processing
  • Generates interactive visualizations for reviewing extracted entities in context
  • Supports both cloud and local LLMs, offering flexibility in model choice
  • No need for model fine-tuning; adaptable using few-shot examples
Cons
  • Requires an API key for cloud-based models like Google Gemini
  • Accuracy depends on model selection, task complexity, and prompt clarity
  • May require careful prompt engineering and high-quality examples for optimal results
  • Only supports Python 3.10 and later

Best For

Extracting characters, emotions, and relationships from literary textsStructuring medication information from clinical notes or reportsOrganizing radiology report findings into structured data (RadExtract)General extraction of structured information from unstructured documents in any domain