MusicReasonProgression and Arranging
What chord fits this melody note?
Choose a key and a melody note. This tool derives every diatonic chord that either contains the melody note as a genuine chord tone, or supports it as an in-key non-chord tone, and states which for each candidate. It never claims to compose a finished arrangement, only to compare compatible starting options.
Answer
Understand
A single melody note is compatible with more than one chord: it might be a chord's root, third, fifth, or seventh, or it might simply be an in-key note that a chord does not contain at all but still supports as a passing or neighbor tone. This tool separates those two cases explicitly rather than collapsing them into one undifferentiated "fits" label.
Worked examples
In C major, a melody note of E paired with a C chord identifies E as the chord's own third, a direct chord-tone match. The same E note is also retained against several other diatonic chords, either as another chord's chord tone or as a supported in-key tension, with the reason stated for each.
Method and limitations
The tool builds the stated key's diatonic degree table, then checks every diatonic chord quality at every degree against the melody note: a chord that contains the note as one of its own declared tones is retained as a chord-tone match, naming which degree (third, seventh, and so on) matched. A chord that does not contain the note, but where the note is still diatonic to the stated key scale, is retained as a supported tension. A chord matching neither test is not retained at all. This launch scope evaluates one melody note at a time rather than a full multi-slot melody fragment, and it never claims to have composed a finished, stylistically complete arrangement.
A note that sits outside the stated key entirely retains no candidates at all: it is neither a declared chord tone of any diatonic chord nor a supported in-key tension, so the result reports no match rather than forcing a weak one. This is a deliberate boundary, since harmonizing a genuinely chromatic melody note needs either a borrowed or a secondary chord this single-note tool does not search for on its own; Modal Interchange Explorer and Secondary Dominant Finder cover those two cases directly.