RAG Guardrails Layered Defense Model No single check is enough. Combine at minimum: scope check , forced citations , groundedness score , schema validation . Forced-Citation Prompting Parse-time check: reject any answer where a sentence lacks . Groundedness Scoring (NLI Entailment) Run a Natural Language Inference model over each pair and require entailment. LLM Self-Check (TRUE-style) Google's TRUE metric: ask a judge LLM whether the answer is entailed by the sources, with a binary output. Cheaper than NLI, no GPU; good default for < 500 QPS. Out-of-Scope Refusal Also refuse when top-K retri…