Other more recent authors include it and many other taxa as subspecies of the blue-tailed emerald (Chlorostilbon mellisugus).

However, as of 2020 BirdLife International's Handbook of the Birds of the World (HBW) retains it in genus Chlorostilbon.

The tail is long and deeply forked, blue-black or black with a blue gloss, and the central two or three pairs of feathers have dark brownish gray tips.

There is a single specimen from Isla Mujeres about 90 km (56 mi) north of Cozumel, and the species is thought to occasionally visit there.

They are assumed to be similar to those of Canivet's emerald, which forages by trap-lining, visiting a circuit of a variety of flowering plants, and also feeds on small arthropods.

The Cozumel emerald's vocalizations are described as similar to those of it close relatives, "dry, rattling and chattering calls".