The invention relates to a bone implant for attaching to on a surface of a bone, including a base body whose lower side and/or upper side correspond(s) substantially to a deformation-free bone outer contour, wherein the outer dimensions of the base body are chosen such that the base body covers a specifically introduced deformation region for obtaining autologous bone material completely, wherein in the base body at least one slot is provided which is dimensioned such that it guides a bone marking and/or bone processing tool inserted in the slot in use.