Philautus acutus was discovered and described by Julian Dring (1987) from the mossy forests of Gunung Mulu, Sarawak, at around 1300 m a.s.l. To our knowledge, all records—including those on iNaturalist—are restricted to this mountain, suggesting that P. acutus is a micro-endemic species confined to Mulu.

This is a medium-sized brown bush frog, with males measuring approximately 23–28 mm in snout–vent length. The body is stocky, and the head is broad and flat. The snout appears rounded from above and slightly truncated in profile. The skin looks relatively smooth at first glance, but close inspection reveals numerous tubercles. The legs are comparatively short. The tips of the toes and fingers bear adhesive discs; the toes are webbed to about one-third of their length, while the fingers show only rudimentary webbing.

The dorsal coloration is brown, typically marked by a large dark patch on the back that continues onto the thighs and shanks when the frog is in resting pose. As in other Philautus species, coloration can vary, and further research is needed to assess the extent of this variation. However, all known live specimens share a distinct reddish iris.

Males call from vegetation between 0.5 and 4 m above the ground, producing a series of sharp, shrill “gree” notes. Our team discovered a froglet still enclosed in its egg jelly beneath the leaf litter, which was confirmed as P. acutus through genetic barcoding (Hertwig et al. 2012). This finding provides unequivocal evidence of direct development in this species.