Cleaving crystals in a vacuum chamber is a simple method for obtaining atomically flat and clean surfaces for materials with a preferential cleaving plane. Most in situ cleavers use parallel cutting edges that are applied from two sides on the sample. We found in ambient experiments that diagonal cutting pliers, where the cleavage force is introduced in a single point instead of a line, work very well also for hard materials. Here, we incorporate the diagonal cutting plier principle in a design compatible with ultrahigh-vacuum requirements. We show optical microscopy (millimeter scale) and atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with this device.