What are the best RAG frameworks?

There isn't one single "best" RAG framework — the three real, actively maintained options worth knowing are LangChain, LlamaIndex, and Haystack, and which one fits depends on what you're actually building. Each is a solid choice; they just optimize for different jobs.

How do LangChain, LlamaIndex, and Haystack differ?

They overlap a lot, but each leans toward a different kind of project:

• LangChain — the most general-purpose of the three, built for LLM apps beyond just RAG. Its LangGraph extension adds agent-style reasoning and tool use, so it's the pick when your system needs to do more than fetch and answer.
• LlamaIndex — a framework built specifically around your data. It's known for strong ingestion, indexing, and querying, including messy formats like tables, PDFs, and images, so it usually needs less glue code for straightforward RAG over your own documents.
• Haystack — deepset's framework, aimed at production-grade search pipelines. It's the go-to when a wrong answer has real consequences (finance, healthcare, legal), because its pipeline structure favors reliability and auditability over quick experimentation.

Do I still need a vector database?

Yes. Whichever framework you pick, you'll pair it with a vector database — something like Pinecone, Weaviate, or Chroma — which stores your document embeddings and does the actual similarity search. The framework is the plumbing that moves data between your documents, the retriever, and the model; the vector database is where your data actually lives and gets searched.

They do different jobs, and a real RAG system needs both.

Which RAG framework should I actually pick?

Be honest with yourself about which situation you're in, because that decides it more than any feature list. Quick prototyping tends to favor LangChain or LlamaIndex. A production search pipeline with compliance needs tends to favor Haystack.

Simple RAG over your own files tends to favor LlamaIndex. There's no universal winner — only the one that matches your actual problem. If you're unsure, start with the one whose defaults get you to a working demo fastest, then switch if you hit a wall.