The yellow wagtail is about the same size as the mountain wagtail, with a body length of 15 to 18 centimeters.The top of the head is blue-gray or dark.The upper body is olive green or gray, with white, yellow or yellow-white eyebrow lines.The flight feathers are dark brown with two white or yellow-white horizontal spots.The tail is dark brown, and the outermost two pairs of tail feathers are mostly white.Underparts yellow.