SWIIFT v0.10: a numerical model of wave-induced sea ice breakup based on an energy criterion Geoscientific Model Development The wave-induced breakup of sea ice contributes to the formation of the marginal ice zone in the polar oceans. Understanding how waves fragment the ice cover into individual ice floes is thus instrumental for accurate numerical simulations of the sea ice extent and its evolution, both for operational and climate research purposes. Yet, there is currently no consensus on the appropriate fracturing criterion, which should constitute the starting point of a physically sound wave--ice model. While fracture by waves is commonly treated within a hydroelastic framework and parametrised with a maximum strain-based criterion, in this study we explore a different, energy-based, approach to fracturing. We introduce SWIIFT (Surface Wave Impact on sea Ice---Fracture Toolkit), a one-dimensional model based on linear plate theory, that can produce time-domain simulations of wave-induced fracture, into which we incorporate this energy fracture criterion. We demonstrate SWIIFT with simple simulations that reproduce existing laboratory experiments of the fracture by waves of an analogue material, allowing qualitative comparisons and validations of the energy fracture criterion. We find that under some wave conditions, identified by a dimensionless wavenumber, corresponding to in situ or laboratory wave-induced fracture, the model does not predict fracture at constant curvature; thereby calling into question the appropriateness of parametrising sea ice fracture with a maximum strain criterion.