The white-tailed jay is overall white and bluish, with a black head. Its face is mostly black, with a small white spot above the eye, a small white moustachial stripe, and a somewhat larger white spot on the cheek. It has a white nape and belly. The back and wings are a greyish-blue, which extends down the top of the tail. The retrices, tail tip, and underside of the tail are white. It has bright yellow irises. There are no visual differences between the sexes. Juveniles have brown irises and lack both the white spot above the eye and the moustachial stripe. These features last until the first moult.
The white-tailed jay is roughly 33 cm (13 in) in length. One individual measured had a wing length of 146 mm (5.7 in), a 147 mm (5.8 in) tail, 40 mm (1.6 in) tarsi, and a 40 mm (1.6 in) beak. Weight measurements come from a single pair, with the male weighing 160 g (5.6 oz) and the female weighing 149 g (5.3 oz).
Little is known of the vocalizations of the white-tailed jay. Their most common call is described as "cha-cha-cha-cha", varying in pitch throughout. It is thought that this may be used socially. They also make a high-pitched "clewp-clewp" call. The white-tailed jay has fewer vocalizations than other species in its genus. This is likely because of its habitat, as it prefers open areas where visual communication is more useful.
The white-tailed jay is unique within its range, with no other species being visually similar. It is visually very similar to the tufted jay but their ranges do not overlap. Additionally, compared to the tufted jay, the white-tailed jay lacks a crest, has white on its outer wings, and less white on its tail.
