You can sort and thematically extend your playlists using the Sort Your Music tool. Just like Smarter Playlists, it was created by Spotify's developer Paul Lamere, and it has a lot of data power—primarily because Sort Your Music accesses an intelligent music platform called The Echo Nest. Harnessing information from over 1.3 billion data points, The Echo Nest's algorithms are able to evaluate every single Spotify song according to certain parameters. You can arrange playlists based on attributes you didn't even know Spotify tracked or made available to you, such as:

Beats per minute (BPM): The tempo of a song
Energy: Echo Nest measures how energetic a song is
Danceability
Loudness
Valence: A song's positive mood
Length
Acoustics
Popularity: An attribute attached to Spotify's own algorithm that determines the popularity of a recent song

Découvert par https://www.vice.com/en/article/59z7vk/hidden-features-and-third-party-programs-that-make-spotify-work-for-you