A tool according to the invention for generating an undercut in a bone including a core with a shank and a stamp mounted on a distal end of the shank, wherein the stamp, in a transition area to the shank, has a run-on bevel ascending in the distal direction, and a cutting sleeve which is arranged to be longitudinally movable on the shank and of which the distal end is formed by at least one segment that can be spread open when pushed onto the run-on bevel, wherein the at least one segment has at least one laterally arranged cutting edge. The invention also relates to a method for generating an undercut in a bone.
