A kunai is a traditional Japanese tool that originated from the masonry trowel. It has a leafshaped blade and a handle with a ring at the end, which can be used to attach a rope. The kunai comes in two main types: the short kunai (shōkunai) and the big kunai (daikunai).

Although primarily a tool used for gardening and masonry, the kunai was also adapted as a multifunctional weapon by ninjas. It could be used for stabbing, thrusting, and even climbing walls. Contrary to popular belief, kunai were not originally designed as throwing weapons, though they can be thrown effectively.

In popular culture, especially in manga, anime, and video games like "Naruto," kunai are often depicted as versatile weapons used by ninjas.