(Disclaimer: Please forgive the simplistic look of this page. I wrote its code myself - aside from linking to the main site's CSS file and reusing some metadata - and my HTML skills are relatively rudimentary. Also, its contents may not be new to you if you read the info page on the main site; I wanted to expand on it and more thoroughly explain some of the decisions I made while selecting songs.)
Sonic Heardle is a clone of Joywave Heardle (which in turn was modeled on Heardle and K-Pop Heardle) that is focused on Sonic the Hedgehog.
Each Sonic Heardle is randomly chosen from one of several songs lifted from the franchise. The vast majority of these come from the games, unsurprisingly - though I want to make it very clear that I am pulling from a very wide array of sources, including beta versions of songs, unused songs, or music from extremely obscure Sonic titles. While I have added a handful of songs from other adaptations (like SatAM and the OVA, among others), I stuck to well-known tracks in their case for the sake of fairness.
In addition, the list includes official remixes of Sonic songs from crossovers (Mario and Sonic, All-Stars Racing, and so on). I am only including Sonic-related songs from these games.
Finally, I should also mention that the site uses the American names for games if they differ across regions (3D Blast instead of 3D: Flickies' Island, spelling Colors without a U, and so on).
If you're an aspiring Heardle maker, I recommend checking out Joywave Heardle's original README. I made the main site by following the instructions there - in fact, this very site's phrasing is modeled on their README. (They themselves were relying on WJSN Heardle's code, editing it for their own project. I figured I should state this for the record.)