When describing motion in physics, the selection of a frame of reference is crucial. The graph of a moving object can look quite different based on the frame of reference. In recent years, various tests have been developed to assess the interpretation of kinematic graphs, but none of these tests have specifically addressed differences in reference frames. Moreover, existing tests that explore differences in reference frame typically focus on the equivalence principle through written answers, interviews, or simple calculations and vector addition; however, none of these tests evaluate position-time graphs. To address this gap in the research, we developed and evaluated the Inventory of Galilean Transformation of uniform linear motion in position-time graphs (IGT). The IGT consists of 15 multiple-choice items that systematically use position-time graphs of linear uniform motion to assess the understanding of 3 types of Galilean transformations: the identity transformation, the transformation between two (opposing) stationary displaced frames of reference, and the transformation from a stationary into a uniformly moving frame of reference. Herein, we presented the development and validation of the IGT.