The Circle of Fifths Trainer drills the 14 major and 14 minor key signatures used in Western music — every key from C major (no accidentals) through F♯ major (six sharps) and G♭ major (six flats), plus every relative minor. Two study modes, three drill directions, all free and mobile-friendly.
Pick which keys to drill (major only, minor only, or both), then choose a direction. Key to accidentals shows you a key name (like "Key of D major") and asks you to mark the F♯ and C♯. Notes to key shows you the seven notes of a scale and asks you to name the key — a slightly harder direction that builds the reverse-association you need for sight-reading and analysis.
A focused drill: see a major key, name its relative minor. The 14 majors cycle through in random order. Useful for internalizing the major/minor pairings — that A minor is the relative minor of C major, that E minor is G major's relative minor, that D minor pairs with F major, and so on through the whole circle.
The circle of fifths is one of the few facts in music theory that genuinely repays drilling. There's no shortcut to knowing that B major has 5 sharps without looking it up — but once it's reflexive you can read any score, transpose any piece, and analyze any chord progression without breaking flow. Best times are stored in your browser; +20 seconds per wrong answer keeps the focus on accuracy.