LangChain

The original LLM application framework, plus a hosted LangSmith side.

Best for A general LLM app framework with a huge ecosystem

LangChain is an open-source framework for building applications on language models, with Python and JavaScript libraries. Chains, tools, and retrieval are the core ideas. LangSmith is the hosted sibling for tracing. Use the library when you want the ecosystem. Use LangGraph, in this directory, when the thing you are building is a stateful agent.

Best use cases

• Retrieval and tool-calling prototypes
• Python or JavaScript services that call models
• Teams that already have LangChain examples in the repo