LangChain

What LangChain is

LangChain is a free, open-source framework for building agents that connect models with tools. Its `create_agent` harness brings together a model, tools, a prompt, and middleware in a configurable setup, with templates for common use cases and a ReAct pattern. Middleware can add human approval, conversation compression, sensitive-data removal, guardrails, retries, routing, and custom tool policies. Agents run on LangGraph’s durable runtime, which supports persistence, rewind, checkpointing, and human-in-the-loop workflows. The framework documents more than 1,000 integrations across chat and embedding models, tools and toolkits, document loaders, and vector stores. Standard interfaces for models and embeddings allow provider changes with minimal code changes. Documentation and installation examples cover Python and JavaScript/TypeScript. LangSmith can trace requests, help debug agent behavior, and evaluate outputs. The LangChain framework costs nothing. LangSmith’s Developer plan costs nothing and includes one seat and up to 5k base traces per month before pay-as-you-go charges.