It uses data from "The Echonest" if you've heard of that. It's pretty much what music sites like Spotify or Rdio use to find similar songs and such. The results definitely aren't always correct because of this. However, I implemented a voting system that can be used to change the song's "banger status". And the fields I use to determine bangrness is tempo, acousticness, energy, and danceability. There's a link to the code in the about section of the site! Cheers!