LangChain is an open-source framework for building applications powered by large language models, providing a standardized set of abstractions and tools for connecting LLMs to external data sources, APIs, and computation. Created by Harrison Chase in late 2022, LangChain has rapidly become one of the most popular frameworks in the LLM application ecosystem, with a large and active developer community. The framework provides composable components for common LLM application patterns including prompt management, chains (sequences of LLM calls), agents (LLMs that decide which tools to use), retrieval-augmented generation (RAG), memory systems, and output parsing. LangChain supports all major LLM providers including OpenAI, Anthropic, Google, Mistral, Cohere, and local models through a unified interface, allowing developers to switch between models with minimal code changes. The LangChain ecosystem includes several key components. LangChain Core provides the base abstractions and the LangChain Expression Language (LCEL) for composing chains declaratively. LangChain Community contains third-party integrations with hundreds of tools, vector stores, document loaders, and services. LangGraph extends the framework with support for building stateful, multi-actor agent applications using graph-based workflows. LangSmith is the companion commercial platform that provides observability, testing, evaluation, and monitoring for LLM applications in production, with tracing capabilities that show every step of a chain or agent execution. LangServe enables deployment of LangChain applications as REST APIs. The core LangChain libraries are free and open-source under the MIT license, available in Python and JavaScript/TypeScript. LangSmith offers a free tier for development, a Plus plan at $39 per seat per month, and custom Enterprise pricing for organizations requiring advanced features and support.
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