Creating models of software systems and analyzing the models helps develop more reliable systems. A well-known software modeling tool-set is embodied by the declarative language Alloy and its automatic SAT-based analyzer. Recent work introduced a novel approach to testing Alloy models to validate their correctness in the spirit of traditional software testing: AUnit defined the foundations of testing (unit tests, test execution, and model coverage) for Alloy, and MuAlloy defined mutation testing (mutation operators, mutant generation, and equivalent mutant checking) for Alloy. This tool paper describes our Java implementation of MuAlloy, which is a command-line tool that we released as an open-source project on GitHub. Our experimental results show that MuAlloy is efficient and practical. The demo video for MuAlloy can be found at https://youtu.be/3lvnQKiLcLE.