"leptomantis belalongensis" is a small, slender frog with a narrow waist. when adult, males measure 38.2 to 30.9 millimeters, and females 34.7 to 25.8 millimeters. the head's width is greater than both its length and the width of the body. the snout is obtuse, with teeth on the upper jawbone, and the canthal ridge is sharp. the loreal region is sloping and oblique, and the nostrils are located closer to the tip of the stout than to the eyes. the irises of the large, protruding eyes are ruby-coloured, diffusing to yellow laterally with a distinct black ring along the margin. the diameter of the faintly visible tympanum equals one-third of that of the eye.