The TrackCheck extension for SoundCloud will detect the tempo and key of the audio track, allowing you to easily compare your tracks with others and easily detect any changes in tempo or key. The song to be analyzed needs to be your song, streamable, and downloadable for the extension to work. 

The app also allows you to find other tracks that are similar to the one you are listening to with respect to tempo and/or key. 

To start using TrackCheck, go to SoundCloud, play a track, and click on the TrackCheck button which appears at the bottom of the transport bar.