A hook knife is an important piece of equipment. It is used in correcting a line over on a slider-up jump where the rig is not equipped with toggles and may also be of more general use in a number of other situations including, for instance, if the canopy is irretrievably stuck in a tree or hanging from a post, suspended by only a few lines.

The most common hook knives (such as that shown to the right) are bright orange, plastic, and manufactured for use as a fish-gutting knife. They are quite easily broken, however — something which could be inconvenient (to say the least) if it occurred while the jumper was attempting to release a lineover. More durable aluminum hook knives are available through skydiving manufacturers; their use is highly recommended.