Blackouts in power grids usually result from cascading faults. The key importance of the electric power grid for society encourages further research into maintaining the reliability of the energy system and developing new methods to manage the risks of cascading blackouts. Appropriate software tools are required to better analyse, understand, and evaluate the consequences of cascading failures. This article presents MATCASC, an open-source MATLAB-based tool for analysing cascading faults in electrical networks. Cascade effects due to line overhead cuts are considered. The applicability of the MATCASC tool is demonstrated by evaluating the robustness of IEEE test systems and real world electrical networks with respect to cascade faults.