The stability of peeling, ballooning, and peeling–ballooning modes, which relate to edge-localized modes, is investigated numerically with the linear ideal magnetohydrodynamic stability code MARG2D. The effects of 'sharpness' on the stability of the peeling–ballooning mode are examined, where the sharpness is defined in terms of the curvature at the top or bottom of the outermost flux surface. It is found that the stability limit of the pressure gradient significantly improves as the sharpness increases even when the ellipticity and the triangularity are unchanged. The sharpness is an important parameter for high performance H-mode operations with high pedestal pressure.