Select the desired key from above radiobutton list, press the submit button. You will now see all the songs in the database with the selected key and the default tempo at 120 Beats Per Minute. Change the BPM value or select the Pitch dropdown box to see more result. To see the compatible tracks, select the "Show Compatible keys" option.

You can also use the seach field in the menu to the left, write a artist name or song title and press enter on your keyboard.

When you see the result list press the youtube icon to view the video for the selected song . The video will now be displayed in the small window to the left. If you want view a bigger version, simply click on the video and a new window will pop up. Remember you might not always get the right video with this solution, the artist and title of the song are sent to youtube and sometimes it will not match the song.

When you see the list of songs you will have a option for finding songs that will mix perfectly with the selected song. Press the heart icon to find all the songs that are compatible.

Most songs in the database are analyzed using Mixed in Key 4.0 software and some are keyed manually by ear using a midi keyboard. There might be errors and duplicate entries with different keys, bare in mind that this tool is just a guide to give you ideas for your next mashup or mix. Always trust your own ears and let this tool be your muse.

If you are looking for a more accurate datebase I highly recommend Mark Davis's Harmonic Mixing key database.
Click here to go to Harmonic-mixing.com site