Chord Key Finder
Score the twelve major and twelve minor keys against a list of chord symbols and show the best five.
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Result
About this tool
Type chord symbols and run the page. The input is split on whitespace, commas, semicolons, and pipes. Each token is parsed as a chord. Tokens that are not chords are dropped. An empty list stops with Enter at least one chord symbol. The scorer then tries all 12 tonics in major and all 12 in natural minor, 24 keys. For each key it builds the seven diatonic triads and looks up every chord's root. A root that is not in the key scores −0.35. A root that is in the key scores 1.3 when the chord's quality matches that degree, and 0.55 when the root fits but the quality does not. Degrees 1, 4, and 5 add a further 0.25. Confidence is the score divided by the chord count times 1.55, times 100, rounded, and clamped between 0 and 100.
C Am F G is the progression to check by hand. It ranks C major at 96 percent. The degree lines are C as I tonic, Am as vi submediant, F as IV subdominant, and G as V dominant. Second is A minor at 88 percent, where those same chords read as III, i, VI, and VII. Then D minor at 80, F major at 80, and G major at 65. In G major the F chord has no degree, so that line says outside key. The report shows five keys. Each block starts with the rank, the key name, and the percent, then a degree line for every chord you typed, in the order you typed them. A major triad is written as the note name. A minor triad keeps the m.
The qualities the parser accepts are the ones the music module names: major, minor, diminished, augmented, dominant seventh, major seventh, minor seventh, half-diminished, suspended 2, and suspended 4. A seventh chord can still land on a triad degree. If the quality is not the triad's quality, that chord gets the softer 0.55 instead of 1.3, plus the cadence bonus when the degree is I, IV, or V. The page does not hear audio and does not estimate a key from a recording. The audio key detector is a different tool. This one only reads the symbols in the box. Confidence is a ranking of this score, not a probability you can quote as certainty. A short list of primary triads scores higher than a list that includes a chord from outside the key, because each outside chord subtracts 0.35 and also raises the chord count in the denominator. The page does not offer modes other than major and natural minor, does not print a roman-numeral analysis of a melody, and does not transpose the chords. Ties keep the sort order of the 24-key loop after the confidence sort, and only five rows are shown.
Example. C Am F G ranks 1. C major - 96%, with C as I tonic, Am as vi submediant, F as IV subdominant, and G as V dominant. A minor is second at 88%. In G major, F is marked outside key.
Limit. Only major and natural minor are scored, and only the top five are shown. The page reads chord symbols. It does not detect a key from audio.
What key is C Am F G?
C major at 96 percent, then A minor at 88, D minor at 80, F major at 80, and G major at 65. In C major the lines are I tonic, vi submediant, IV subdominant, and V dominant. In the G major row, F is outside the key.
How is the percent calculated?
Each chord adds 1.3 when its root and quality match a degree, 0.55 when only the root matches, or −0.35 when the root is outside the key. Degrees 1, 4, and 5 add 0.25. The total is divided by the chord count times 1.55, multiplied by 100, and rounded.
Which separators can I use?
Spaces, commas, semicolons, and pipes. C, Am, F, G is the same list as C Am F G. A token that is not a chord is dropped. An empty box stops with Enter at least one chord symbol.
Will this listen to a song?
No. It only scores the symbols you type against 12 major keys and 12 natural minor keys. A recording belongs on the audio key detector, which uses a pitch trace rather than chord names.