Performance Testing RAG Applications: Complete Engineering Guide

In this blog post, we will see how to performance test a RAG (Retrieval-Augmented Generation) application properly, covering both speed and correctness, and how to wire both into a CI/CD pipeline so regressions get caught before they reach production. Performance testing a RAG application requires two separate testing gates: one for speed and one for answer quality. Traditional load testing tools measure response times but cannot detect hallucinations, where a model returns fast but factually incorrect answers grounded in fabricated context rather than retrieved documents. The guide demonstrates using k6 for load testing end-to-end latency and DeepEval for evaluating faithfulness and answer relevancy using an LLM-as-judge approach. Both gates are integrated into a GitHub Actions CI/CD pipeline so regressions in either performance or output quality are caught automatically on every pull request before reaching production. If you've come from a JMeter or k6 background like I have, your first instinct with a RAG endpoint is probably to point a load test at it and check response times. That gets you halfway there. A RAG app can return a fast, confident, completely wrong answer, and a plain load test will never tell you that. You need two testing surfaces, not one: performance and quality. This guide covers both, using a single running example throughout: a documentation assistant that answers "How do I run JMeter in non-GUI mode?" against a small knowledge base. Why RAG breaks traditional load testing assumptions A conventional API returns a complete response and you measure the round trip. A RAG endpoint does two expensive things before it answers: it retrieves context from a vector store or search index, then it streams a generated response token by token. That second part matters a lot. A single request can stream hundreds of tokens over several seconds, so "request duration" as a single number hides two very different problems: how long the model took to start answe