Surface strains in core–shell nanoparticles modify catalytic activity. Here, a continuum-based strategy enables accurate surface-strain-based screening and design of core–shell systems using minimal input as a means to enhance catalytic activity. The approach is validated here for Pt shells on CuxPt(1–x) cores and used to interpret experimental results on the oxygen reduction reaction in the same system. The analysis shows that precise control of particle sizes and shell thicknesses is required to achieve peak activity, rationalizing the limited increases in activity observed in experiments. The method is also applied to core–shell nanorods to demonstrate its wide applicability.