Brag's a good dog, but that he hath lost his tail.

The dog’s flattering name and the praise it receives are undercut by an obvious defect. A boast sounds less convincing when it leaves out an important qualification.

The proverb makes room for some merit while poking fun at exaggerated praise. A conspicuous shortcoming can change how an otherwise favorable claim is heard.

Use the proverb as a wry reply to praise that overlooks a significant drawback in a person, plan, or achievement. It qualifies an overconfident claim rather than dismissing everything being praised.