The Eyelash Viper is a small or medium-sized snake that can grow up to 95 cm in length, adults range from 50 to 70 cm long. The females tend to be longer and more robust than males. The body is relatively thin and they have a flat head, clearly differentiated from the neck, and are snub-nosed. As with other members of their genus, the Eyelash Viper has a relatively short prehensile tail. Their most relevant distinction is the set of modified scales projecting above their eyes that look very similar to eyelashes; this is the characteristic that gave it its common name Eyelash Viper. This species has a wide range of base colors, including gray, brown, yellow, gold, and even pink and white. The color pattern also varies and is made up of complex designs. These designs help identify different individuals based on their colors. Some yellow or golden Eyelash Viper individual are popularly known as oropel (golden morph), and are mistakenly considered a different species. This is incorrect, because yellow is simply one of the many colors this species can display.

The Eyelash Viper is an arboreal species, usually active at night. Its geographic range is very wide: on the Caribbean from the northeast in Mexico to the northwest in Venezuela; and on the Pacific from the southeast of Costa Rica to Ecuador. In Costa Rica it can be found from the sea level to 1500 m of altitude