Oxide glasses are disordered molecular structures and typically show poor intrinsic ductility. As a consequence, these materials are brittle. Although it is possible to toughen glasses using additives or heat-treatment methods, their resistance to crack formation and propagation remains very low. To address this long-standing challenge, one strategy is to look at the molecular design of the glass and to tune its composition. By enabling the formation of weak ionic bonds, it has been possible to develop glass compositions that exhibit high crack resistance through the plasticity of their molecular network.