A planetary variator, which is a type of the continuously variable transmission (CVT), is described in terms of dynamical modeling and assessment of its efficacy in the tuned mass damper with a variable inerter (TMDVI). An off-the-shelf planetary variator is used and modified for this application. Then, kinematic and dynamic models of the device are developed and its parameter values are determined. In the next step, the model is validated experimentally. In the second, theoretical part of the paper, an implementation of the modified device as a part of the TMDVI is considered. The variator enables tuning of the natural frequency of the TMDVI to the current frequency of excitation and allows the resonance frequency to be crossed via an optimal path with a low oscillation amplitude of the main body. Additionally, the previously proposed method to control the TMDVI to obtain efficient mitigation of vibrations in a wide range of excitation frequencies is extended. • The paper presents experimental examination of a planetary variator. • We derive validated mathematical model of a planetary variator. • We show possible application of a variator as a part of a tuned mass damper with variable inertance. • We propose an optimization method that allows efficient mitigation of vibrations. • We show response of a damped system with optimized damper.