We present Tolerange, an open source tool tailored for measuring the masking fault-tolerance provided by stochastic systems. Tolerange takes as input a nominal model of a system together with the fault-tolerant version of it, both written in a Prism-like notation, and it computes the expected number of faults that the system’s fault-tolerant version is able to mask. Our tool supports the analysis of randomized algorithms including the description of faults as probabilistic actions. It combines techniques coming from game theory, linear programming, and probabilistic transition systems. In this paper we describe the tool as well as its use to measure the masking fault-tolerance of some well-known examples.