Considering a semi-infinite crack propagating within a plane where the local fracture energy fluctuates due to the presence of microstructural heterogeneities, we emphasize the decisive influence of the material disorder on the effective fracture energy of the composite at a macroscopic scale. Through the use of large-scale numerical simulations of a crack interacting with tough inclusions of varying shape, we show how the disorder intensity and the inclusion geometry modify both quantitatively and qualitatively the toughening behavior with respect to the periodic case, where the inclusions are arranged in an ordered manner. This disorder-induced toughening is then rationalized using a theoretical homogenization framework borrowed from statistical physics. It ultimately allows to propose strategies for the design of disordered composites with improved crack growth resistance and tailored asymmetric fracture properties.