Leptobrachella sarawakensis is a slender litter frog inhabiting lowland rainforests in southwestern Sarawak. It appears to tolerate secondary forests and moderate human disturbance. Morphologically, the species cannot be reliably distinguished from the sympatric L. gracilis. In their original description, Matsui et al. (2025) separated the species primarily on the basis of acoustic and genetic evidence. As a consequence of this taxonomic change, it remains uncertain whether the images presented for L. gracilis on this website depict L. sarawakensis, L. gracilis, or a mixture of both.

Leptobrachella sarawakensis is a medium-sized species. Males reach approximately 31–36 mm and females 41–48 mm in snout–vent length. Compared with L. gracilis, males of L. sarawakensis are smaller, but otherwise the two species are morphologically similar. The snout is obtusely pointed and rounded in profile, projecting slightly beyond the lower jaw. The eyes are large and the canthus rostralis is distinct. Limbs are slender; the third finger and fourth toe are the longest. Digits terminate in rounded, but not enlarged, tips. The outer metatarsal tubercle is absent. A low supratympanic fold is present, and the eardrum is distinct but small.

The skin is generally smooth, though scattered small tubercles of varying size are present.

Coloration ranges from brown to grey, usually with dark dorsal markings. The flanks bear light warts interspersed with dark spots. The underside is predominantly white with dark brown spotting. The upper sector of the iris is orange to amber. The upper arm and elbow are cream-colored. For general appearance, see the page for L. gracilis.

The calls of L. sarawakensis and L. gracilis differ clearly: L. sarawakensis produces calls with a faster repetition rate of notes and a higher dominant frequency. According to Matsui et al. (2025), these differences are not only measurable but also audible to the trained ear, though practical distinction in the field will likely require experience with calls of both species.