Why does this chord progression work?
Paste the chords. You get the likely key, the Roman numerals and what stands out β free, and calculated rather than guessed.
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What this handles
Supported
- Triads: C, Am, Bdim, Caug
- Sevenths: G7, Cmaj7, Dm7, Fβ―m7β5, Bdim7
- Suspended and added: Csus4, Csus2, Cadd9, C6
- Extensions: C9, Cm11, C13, C7β9, C7β―11
- Slash chords: C/E, G/B
- Sharps and flats: Fβ―, Bβ, Dβm7
Not supported
- Audio, MIDI or sheet-music files
- Melodies, lyrics or specific voicings
- More than 24 chords at a time
Chord symbols carry no melody and no voicing, so the analysis describes harmony only.
How this works
The key, the Roman numerals and the chord spellings are computed by the same tested music-theory code that generates the reference pages on this site. The written report is produced by an AI model working from those calculations β it explains and interprets them, it does not recalculate them.
Harmonic interpretation is genuinely ambiguous sometimes, especially without a melody. Where more than one reading fits, the tool says so rather than picking one and sounding certain.
Only want the key? The free key finder weighs every major and minor key against your chords and shows the evidence for each, and the free Roman numeral analyzer shows what every chord is doing β its numeral, its function and how it connects to the next.