If you’re familiar with mixing in key, then you know the challenge is to figure out how to arrange your tracks to have harmonic mixes. That’s what Mixtool does. Just click "Sort to mix in key", and it will optimize your mix for the most harmonic mixes. You can then drag and drop tracks to reorder them, since there are other considerations besides harmony in mixing. Mixtool automatically detects and displays where harmonic mixes are.
Save a mix, and a button will appear for it at the top. If you want to revert back to the last time you saved, click the mix button. (Mixes are saved in cookies, so they will only be available on the browser you save them on.)
Finding the key of a track is easy if it’s on Beatport- click the search button by the track name and a new window will open with a Beatport search for your track, you’ll find the key there. Otherwise, you could use a key-detection software like Mixed-In-Key. As of yet, no site with an adequate catalogue of electronic music has an API for accessing the key of a track.
Mixtool uses the circle of fifths to find tracks that will mix in key with the key of the track you enter. For each key, there are four keys that will mix harmonically. Those keys are displayed to the right of the key pullodown menu on each track. When harmonic mixes are displayed, you will see the type of harmonic mix: same key, key up, key down, or major-minor.