LangChain

LangChain is the most widely adopted framework for building applications powered by large language models. It provides abstractions for prompt management, LLM chains, retrieval-augmented generation (RAG), agent systems, and tool integration. The framework supports virtually every LLM provider, vector database, and external tool, making it a versatile foundation for AI applications. LangSmith, the companion platform, provides observability, testing, and evaluation tools for production LLM applications. LangChain is available in both Python and JavaScript, with an active community contributing integrations, templates, and best practices. It has become a de facto standard for LLM application development.