Line Cookies are circular disk shaped non-directional markers to denote a specific location or circumstance on the line. They are often used to mark reference points, intersections, line gaps (i.e. jumps), or the presence of a diver on the guideline.

Early cave divers used clothespins as non-directional markers. However, clothespins were not durable and tended to break or fall off the line. Daniel Riordan, a cave diving instructor, experimented with other options for non-directional markers that would be durable and stay on the line. While working at a dive shop in Mexico, Daniel found a solution using a plastic disk and refined it over several versions. They became popular and eventually Dive Rite purchased the idea to begin mass producing a commercial version of the line cookie.