The White-bellied Tody-Tyrant is a tiny bird with a large voice; its simple song, of two or three sharp notes, is a frequent sound in the humid lowland forests of western Amazonia. This species forages in the under- and midstory of forest; it is easy to overlook, until it begins to call, or makes a short sally to nearby foliage to capture an insect. It perhaps is most common in southeastern Peru and adjacent regions, but the distribution extends north to the south bank of the Amazon, and east to the lower Rio Tocantins in eastern Amazonian Brazil; there also is a disjunct subspecies in northeastern Brazil. The White-bellied Tody-Tyrant has a very simple plumage pattern, primarily light olive green above and grayish white below, and it has a pale iris. The White-bellied Tody-Tyrant formerly was included in the same species as the yellow-bellied White-eyed Tody-Tyrant (Hemitriccus zosterops) of northern Amazonia.