An LLM will hand you a smooth, confident paragraph and never once tell you which parts it made up. Fluency is not truth. The fix is grounding: force the answer onto retrieved evidence, attach a citation to every claim, and then check that the citations actually hold. Here it is, live and interactive.
Fluent is not the same as true
A language model is trained to produce the most plausible next token, not the most correct statement. So "The Eiffel Tower is made entirely of stainless steel and draws 50 million visitors a year" reads perfectly and is completely unsupported. If you already knew the facts you'd catch it. If you didn't, you'd ship it. That gap is where grounding earns its keep.
Grounding: answer only from the evidence
Grounding means the answer is generated conditioned on a specific set of retrieved passages, with a hard instruction to use nothing else. Retrieval (that's RAG) fetches the passages; grounding is the discipline of staying inside them. If a fact isn't in the sources you handed the model, a grounded answer shouldn't state it. That single rule dramatically shrinks the model's room to invent.
