LangChain

LangChain is an open-source framework for building LLM applications, available in Python and JavaScript for composing retrieval, agents, and chains. It supports retrieval-augmented generation through built-in integrations with vector databases and document loaders.

What's notable is breadth of integration: agent components let LLMs select and invoke external tools and APIs, and it supports multiple model providers including OpenAI, Anthropic Claude, and Google Gemini through dedicated integrations.

LangChain fits developers who want a provider-agnostic base for RAG and agent apps. It is less suited to teams wanting stability — frequent framework updates and version migrations have historically required non-trivial code refactors — and to newcomers, since the documentation breadth and shifting recommended patterns can be overwhelming. Note that the LangSmith observability and tracing platform imposes usage limits on the free tier.

Against other LLM app frameworks, LangChain's position comes from its wide provider and tool coverage rather than a single opinionated path.