No — dangerous
No — never. Grapes and raisins can cause sudden kidney failure in dogs, and unlike chocolate there is no known “safe dose”. Some dogs react to just a few grapes.
Scientists long struggled to identify the toxin, but tartaric acid in grapes is now the leading suspect. Sensitivity varies hugely between dogs: one dog may eat a bunch with no visible effect while another develops acute kidney failure after a handful. Raisins and sultanas are even more concentrated and appear in many baked goods — raisin bread, cookies and cereal are common accidental sources.
None. Because there is no established safe amount and the consequence (kidney failure) can be irreversible, vets treat any grape or raisin ingestion as an emergency. If your dog ate grapes or raisins — even a few — call your vet immediately; inducing vomiting within a couple of hours can prevent absorption.
For a sweet, juicy treat dogs can safely enjoy, try seedless watermelon, blueberries or apple slices without the core.
This article is general information, not veterinary advice. If your pet has eaten something potentially harmful or shows symptoms, contact your vet or an emergency clinic immediately. Full disclaimer.