We’ve seen plugins that are designed to tell you the key of a particular song, but now there’s a freely accessible website, GetSongKey.com, that features a database of key and other information for more than six million tracks.
You can search by song, artist or album, and if the song is included, you can learn several potentially useful things about it. As well as the key and the notes in its scale, there are also suggestions on the best keys to modulate to, along with harmonic mixing information for DJs. Each track is also scored in four categories - Positiveness, Danceability, Energy and Acousticness - and similar songs are suggested, too.
There are obvious benefits here for DJs who want to find tracks that work well together, but remixers, songwriters and those wanting to create mash-ups might also learn something useful.
There are various other tools on the site, too: Key Transposer will transpose any given chord progression into a different key; the Key Notation Converter shows you the corresponding Camelot and Open keys for each standard musical key; and Key from Chords tells you the key of a song based on the chord progression.
There’s also a sister site, GetSongBPM.com, which provides tempo information for songs and includes a built-in metronome. You can also find the BPM of any song, either by uploading an audio file or installing a Chrome extension that works on most streaming sources (though not Soundcloud at this time).