The adult crowned woodnymph is 10.2 cm long and weighs 4.5 g. It has a violet crown, upper back, shoulders and belly, a shiny green throat and breast, green lower back, and a deeply forked blue-black tail. The female is 8.4–9 cm long and weighs 3.5 g. She is bright green above and duller green below, with a grey throat and breast. Her tail is rounded, mainly green near the body but with a blue-black lower half and white corners. Young males lack any violet or iridescence and are bronze-coloured below. Immature females have buff fringes on the feathers of the nape, face and rump. The call is a high-pitched fast kip.