Boston terriers are usually born with short tails. The American Kennel Club states that they are either straight or kinked. The tail is set low on the hind quarters and is generally quite thin and tapered.
The American Kennel Club breed standard states that a dog with a docked tail does not meet the breed standard and would be disqualified from competition. To meet the breed standard, Boston terriers need to be small, short-coated, strong dogs that are muscular in appearance. They can be brindle, black or seal in color, but they must also have the white markings that make the breed so distinctive.