Kunai made in Catia V5 and rendered in Keyshot Pro 10.

A kunai (苦無, kunai) is a Japanese tool thought to be originally derived from the masonry trowel.[1] The two widely recognized variations of the kunai are short kunai (小苦無 shō-kunai) and the big kunai (大苦無 dai-kunai). Although a basic tool, in the hands of a martial arts expert, the kunai could be used as a multi-functional weapon. The kunai is commonly associated with the ninja, who used it to gouge holes in walls.

A Kunai normally had a leaf-shaped wrought blade in lengths ranging from 20 cm to 30 cm and a handle with a ring on the pommel for attaching a rope. The attached rope allowed the kunai's handle to be wrapped to function as a grip, or to be strapped to a stick as a makeshift spear; to be tied to the body for concealment; to be used as an anchor or piton, and sometimes to be used as the Chinese rope dart. Contrary to popular belief, kunai were not designed to be used primarily as throwing weapons. Instead, kunai were primarily tools and, when used as weapons, were stabbing and thrusting implements.

Varieties of kunai include short, long, narrow-bladed, saw-toothed, and wide-bladed. In some cases, the kunai and the shikoro, a wide-bladed saw with a dagger-type handle, are difficult to distinguish.