Minimal RAG Implementation: Building a Local Document Q&A System with FAISS and Mistral

This project shows how to implement a local Retrieval-Augmented Generation (RAG) system with just a few lines of Python code, combining FAISS vector search and the open-source Mistral 7B model. It can run document Q&A without a GPU. The project aims to lower the entry barrier for RAG technology, help learners intuitively understand core principles, and support local deployment to protect data privacy.

Large Language Models (LLMs) have a knowledge cutoff limitation—once trained, their internal knowledge is fixed, so they can't answer about events after the training data or access private documents. RAG technology retrieves relevant information from external knowledge bases before generating answers, inputting the results along with the user's question into the model. This preserves general language capabilities while enabling answers based on the latest and most relevant information.

The ai-simple-rag project uses minimal code to demonstrate core RAG components (document loading, vector indexing, similarity search, text generation) with a clear educational purpose. For technology selection: vector search uses Meta's open-source FAISS library (fast, low memory, CPU-friendly); the language model uses Mistral 7B Instruct (open-source, instruction-tuned for Q&A). This combination supports local deployment, so data never leaves the device.

System workflow: 1. Documents placed in the specified data folder are loaded automatically; 2. Documents are split into text chunks, converted to vectors via an embedding model, and a FAISS index is built; 3. The user's question is converted to a vector, and similar text fragments are retrieved; 4. The fragments and question are input as a prompt to Mistral to generate an answer. This reflects the classic RAG architecture: the retrieval module locates information, and the generation module organizes the answer.

Deployment steps are simple: clone the repository, install dependencies, get a Lamini API key. The project provides a precompiled FAISS wheel for Windows/Python3.11, with guidance for other environments. It can run on CPU alone, lowering the entry barrier—even ordinary laptops can experience RAG technology.

The project uses concise code to show the essence of RAG (vector search + LLM generation), helping beginners avoid the complex learning curve of frameworks like LangChain and understand core principles. Application scenarios include: RAG technology entry learning, local sensitive document Q&A prototype development, teaching demonstrations, and as base code for complex systems.

As an educational project, its functions are limited (no multi-turn dialogue, complex document parsing, or advanced retrieval strategies). Production environments need to consider details like long document processing, dialogue history management, and retrieval optimization. It is recommended to start with this project, understand the principles, then explore advanced features—progressive learning is more solid.