The Key Signature Identifier answers the question every student asks when a new piece lands on the stand. Count the sharps or flats at the start of the staff and it tells you the major key, its relative minor, the order of the accidentals and the rule for reading them. Or tap the notes you can see in the music on a keyboard and it ranks the likely keys with a confidence score, including minor keys with a raised leading tone.
Each result shows the scale with playback, the chords you will meet in that key and a common progression, so you know what to expect before you play.