LlamaIndex

LlamaIndex (formerly GPT Index) is a data framework for building LLM-powered applications that connect to external data sources. It specializes in data ingestion, indexing, and retrieval, providing connectors for 160+ data sources (PDFs, databases, APIs, Slack, Notion, etc.) and various index structures (vector, keyword, knowledge graph, tree). LlamaIndex handles the RAG pipeline from document loading through query engines, with built-in re-ranking, query transformation, and response synthesis. It is often used alongside agent frameworks like Pydantic AI or LangChain for the retrieval layer.