A shaping tool for a device for rounding a spine region and for shaping a folding region of a lying outstretched book cover, the folding region being adjacent on either side of the spine region, in accordance with a shape of a spine of a book block, which subsequently forms a book together with the book cover, includes a fixed, convex central shaping strip. Two convex outer shaping rails laterally adjoin the central shaping strip and are laterally adjustable according to a required rounding and width of the spine region of the book cover.