R. grylio reaches a length of up to 165 mm. It has a green to dark brown dorsum scattered with irregular dark markings. The throat and ventral and posterior surfaces of the hind legs can be heavily mottled, or the venter may be immaculate. It has no dorsolateral folds, but it does have a pointed snout, fully webbed toes, and a fourth toe which is only slightly longer than the adjacent toes. The young have dorsolateral stripes like Rana virgatipes.