Melodle is a small daily puzzle for your ears. It plays a short tune of five notes and asks you to name the musical intervals between them: a minor third up, a perfect fifth down, and so on.
Every guess plays back as it's marked, so you hear how close you came as well as see it. Practising like this, naming what you hear, is called ear training, and it's how musicians learn to play what they hear in their head.
New to intervals? Start with the practice tunes after today's puzzle. The arrows on each mark tell you which way to go, and most people get a feel for thirds and fifths within a few days.