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MIT-licensed Python/JavaScript framework for building LLM agents, with 1,000+ model and tool integrations
LangChain is an open-source framework for building agents and LLM applications, giving developers prebuilt agent architectures, middleware hooks and integrations with more than a thousand models, tools and data sources so providers can be swapped without rewriting the app. It ships for Python and JavaScript and, in current versions, runs on the LangGraph runtime for persistence, checkpointing and human-in-the-loop control. The framework itself is MIT-licensed and free; LangChain, Inc. earns revenue from LangSmith, its commercial platform for observability, evaluation and deployment.
The framework is MIT-licensed and free to use with no seat or usage fees. The company monetizes LangSmith — hosted observability, evaluation and deployment — which is priced separately.
Use tool ↗The default starting point for agent development: no other framework matches its integration catalog, documentation volume or hiring-market familiarity. The catch is churn and depth — major versions have repeatedly rewritten core APIs, and once you need observability or managed deployment you are steered toward the paid LangSmith platform.
Watch out: Most tutorials in the wild target older LangChain APIs; check the version before copying code, or you will spend the afternoon on import errors.
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