Validating the RAG Answer Before the User Sees It: Spans, Quotes, and the Feedback Loop

Even when a RAG system produces a structured answer, it requires rigorous verification, as the model may cite lines outside the input, misquote sources, or fail to follow the requested format. A robust post-generation validation process is therefore essential, meticulously checking the answer's shape against the expected schema and verifying that every quote is backed by evidence in the source text. Ensuring a quote is truly "verbatim" is surprisingly complex, requiring normalization for whitespace while still catching subtle but critical errors like off-by-one line number citations. When an answer fails these checks, the system can dynamically respond by retrying with a stricter prompt, flagging the output for human review, or rejecting it outright to prevent misinformation from reaching the user.