Ansonia spinulifer is a common lowland stream toad known from many places in Sarawak. Calling males can be found at night, sitting and calling from low vegetation close to streams. A. spinulifer is easy to recognise: there are big spinose warts on the dorsum and usually a light spot between the shoulders. The warts are large and have keratinized projections, giving the species its name. The base color is blackish with interspersed brown to red tones. 

Adult males are 30–40 mm snout-vent length, females are up to 45 mm.

Ansonia spinulifer tadpoles show the typical sucker mouth of rheophilous Ansonia tadpoles. The mouthparts are shown on the lower image. There are double rows of submarginal papillae. The upper jaw is divided, the lower undivided. The upper lip bears two keratodont rows, the lower three; all rows undivided. The upper side is dark brown with some silver-golden dusting. Dark pigmentation extends onto the tail and the tail fin margins are also pigmented (faintly visible on the image against the black background). Note the extent of the tail fin relative to other Ansonia tadpoles.