Multiple tools can assist developers when debugging programs, but only a few solutions specifically target the common case of regression failures, to provide a more focused and effective support to debugging. In this paper we present RADAR, a tool that combines change identification and dynamic analysis to automatically explain regression problems with a list of suspicious differences in the behavior of the base and upgraded version of a program. The output produced by the tool is particularly beneficial to understand why an application failed. A demo video is available at http://www.youtube.com/watch?v= DMGUgALG-yE