: All chords for one melody note Sorry folks for any confusing For example, let’s say that you have a G. It could belong to the chords G, Gm, C, Cm Em, Dsus4, Eb, A7, Am7, and a bunch more. Is there a online tool where

A good exercise for this is to consider the chord formed when the note is put over all 12 possible chord roots. With C as an example, C as the root makes any kind of C chord. D? as the root means maj7 chords, and maybe m(maj7) chords. D means m7 and 7 chords, E? means 6 chords, 13th chords. You see where this is going, and the possibilities are limited only by what you can come up with. That's the fastest way I know to determine what you're asking.

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you're searching the root tone of your song?

It doesn't make much sense to identify the key from a single starting point, as it can be actually the root tone, the 3rd, 5th (up-beat) or any an approach-note. You'll be more successful by identifying the final chord (here the the final tone is usually the root tone) or the chord of the first measure (but also here the melody tone is not just the root). The best is if you poste a sequence of notes, a motive or a melodic pattern, then you can say whether the song is in minor or major, or a modal key. Indeed you can harmonize a G with any chord as it can be the root, the 3rd, the 5th, or any diatonic or chromatic approach.

for beginners:
tamingthesaxophone.com/jazz-theory-beginners
for advanced:
en.wikibooks.org/wiki/Music_Theory/Complete_List_of_Chord_Patterns

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I would suggest that the question relies on a false (actually "incomplete") assumption. Notes and chords (in most music) are not isolated entities. There is a context (rhythm, melody, harmony) which affects the relation between a melody note and possible chords.

This is a big topic and one learns it gradually by study, listening, playing, and composing. (I can't really shrink the topic adequately in a short answer.)

In classical (common practice period) music, any note may be use with any chord in any key if the context allows.

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Finding or generating chords that have a given note is not rocket science and is IMO a basic skill you should have. But here's a "tool" that's "online" and is not an external resource. You can save or print out an offline version. I generated the list with a Python script (code included at the end) and the music21 library. There may be errors. Sharps only listed, no flats.

Chords with a C

C, Cm, C+, Cdim, C7, CM7, Cm7, Cdim7, C7+, Cm7b5, CmM7, C6, Cm6, C9, CMaj9, Cm9, C11, CMaj11, Cm11, C13, CMaj13, Cm13, Csus2, Csus4, C#M7, C#mM7, C#Maj9, C#Maj11, C#Maj13, D7, Dm7, D7+, Dm7b5, D9, Dm9, D11, Dm11, D13, Dm13, D#dim7, D#6, D#m6, D#13, D#Maj13, D#m13, E+, E7+, F, Fm, F7, FM7, Fm7, FmM7, F6, Fm6, F9, FMaj9, Fm9, F11, FMaj11, Fm11, F13, FMaj13, Fm13, Fsus2, Fsus4, F#dim, F#dim7, F#m7b5, G11, GMaj11, Gm11, G13, GMaj13, Gm13, Gsus4, G#, G#+, G#7, G#M7, G#7+, G#6, G#9, G#Maj9, G#11, G#Maj11, G#13, G#Maj13, Am, Adim, Am7, Adim7, Am7b5, AmM7, Am6, Am9, Am11, Am13, A#9, A#Maj9, A#m9, A#11, A#Maj11, A#m11, A#13, A#Maj13, A#m13, A#sus2

Chords with a C#

C#, C#m, C#+, C#dim, C#7, C#M7, C#m7, C#dim7, C#7+, C#m7b5, C#mM7, C#6, C#m6, C#9, C#Maj9, C#m9, C#11, C#Maj11, C#m11, C#13, C#Maj13, C#m13, C#sus2, C#sus4, DM7, DmM7, DMaj9, DMaj11, DMaj13, D#7, D#m7, D#7+, D#m7b5, D#9, D#m9, D#11, D#m11, D#13, D#m13, Edim7, E6, Em6, E13, EMaj13, Em13, F+, F7+, F#, F#m, F#7, F#M7, F#m7, F#mM7, F#6, F#m6, F#9, F#Maj9, F#m9, F#11, F#Maj11, F#m11, F#13, F#Maj13, F#m13, F#sus2, F#sus4, Gdim, Gdim7, Gm7b5, G#11, G#Maj11, G#m11, G#13, G#Maj13, G#m13, G#sus4, A, A+, A7, AM7, A7+, A6, A9, AMaj9, A11, AMaj11, A13, AMaj13, A#m, A#dim, A#m7, A#dim7, A#m7b5, A#mM7, A#m6, A#m9, A#m11, A#m13, B9, BMaj9, Bm9, B11, BMaj11, Bm11, B13, BMaj13, Bm13, Bsus2

Chords with a D

C9, CMaj9, Cm9, C11, CMaj11, Cm11, C13, CMaj13, Cm13, Csus2, D, Dm, D+, Ddim, D7, DM7, Dm7, Ddim7, D7+, Dm7b5, DmM7, D6, Dm6, D9, DMaj9, Dm9, D11, DMaj11, Dm11, D13, DMaj13, Dm13, Dsus2, Dsus4, D#M7, D#mM7, D#Maj9, D#Maj11, D#Maj13, E7, Em7, E7+, Em7b5, E9, Em9, E11, Em11, E13, Em13, Fdim7, F6, Fm6, F13, FMaj13, Fm13, F#+, F#7+, G, Gm, G7, GM7, Gm7, GmM7, G6, Gm6, G9, GMaj9, Gm9, G11, GMaj11, Gm11, G13, GMaj13, Gm13, Gsus2, Gsus4, G#dim, G#dim7, G#m7b5, A11, AMaj11, Am11, A13, AMaj13, Am13, Asus4, A#, A#+, A#7, A#M7, A#7+, A#6, A#9, A#Maj9, A#11, A#Maj11, A#13, A#Maj13, Bm, Bdim, Bm7, Bdim7, Bm7b5, BmM7, Bm6, Bm9, Bm11, Bm13

Chords with a D#

Cm, Cdim, Cm7, Cdim7, Cm7b5, CmM7, Cm6, Cm9, Cm11, Cm13, C#9, C#Maj9, C#m9, C#11, C#Maj11, C#m11, C#13, C#Maj13, C#m13, C#sus2, D#, D#m, D#+, D#dim, D#7, D#M7, D#m7, D#dim7, D#7+, D#m7b5, D#mM7, D#6, D#m6, D#9, D#Maj9, D#m9, D#11, D#Maj11, D#m11, D#13, D#Maj13, D#m13, D#sus2, D#sus4, EM7, EmM7, EMaj9, EMaj11, EMaj13, F7, Fm7, F7+, Fm7b5, F9, Fm9, F11, Fm11, F13, Fm13, F#dim7, F#6, F#m6, F#13, F#Maj13, F#m13, G+, G7+, G#, G#m, G#7, G#M7, G#m7, G#mM7, G#6, G#m6, G#9, G#Maj9, G#m9, G#11, G#Maj11, G#m11, G#13, G#Maj13, G#m13, G#sus2, G#sus4, Adim, Adim7, Am7b5, A#11, A#Maj11, A#m11, A#13, A#Maj13, A#m13, A#sus4, B, B+, B7, BM7, B7+, B6, B9, BMaj9, B11, BMaj11, B13, BMaj13

Chords with an E

C, C+, C7, CM7, C7+, C6, C9, CMaj9, C11, CMaj11, C13, CMaj13, C#m, C#dim, C#m7, C#dim7, C#m7b5, C#mM7, C#m6, C#m9, C#m11, C#m13, D9, DMaj9, Dm9, D11, DMaj11, Dm11, D13, DMaj13, Dm13, Dsus2, E, Em, E+, Edim, E7, EM7, Em7, Edim7, E7+, Em7b5, EmM7, E6, Em6, E9, EMaj9, Em9, E11, EMaj11, Em11, E13, EMaj13, Em13, Esus2, Esus4, FM7, FmM7, FMaj9, FMaj11, FMaj13, F#7, F#m7, F#7+, F#m7b5, F#9, F#m9, F#11, F#m11, F#13, F#m13, Gdim7, G6, Gm6, G13, GMaj13, Gm13, G#+, G#7+, A, Am, A7, AM7, Am7, AmM7, A6, Am6, A9, AMaj9, Am9, A11, AMaj11, Am11, A13, AMaj13, Am13, Asus2, Asus4, A#dim, A#dim7, A#m7b5, B11, BMaj11, Bm11, B13, BMaj13, Bm13, Bsus4

Chords with an F

C11, CMaj11, Cm11, C13, CMaj13, Cm13, Csus4, C#, C#+, C#7, C#M7, C#7+, C#6, C#9, C#Maj9, C#11, C#Maj11, C#13, C#Maj13, Dm, Ddim, Dm7, Ddim7, Dm7b5, DmM7, Dm6, Dm9, Dm11, Dm13, D#9, D#Maj9, D#m9, D#11, D#Maj11, D#m11, D#13, D#Maj13, D#m13, D#sus2, F, Fm, F+, Fdim, F7, FM7, Fm7, Fdim7, F7+, Fm7b5, FmM7, F6, Fm6, F9, FMaj9, Fm9, F11, FMaj11, Fm11, F13, FMaj13, Fm13, Fsus2, Fsus4, F#M7, F#mM7, F#Maj9, F#Maj11, F#Maj13, G7, Gm7, G7+, Gm7b5, G9, Gm9, G11, Gm11, G13, Gm13, G#dim7, G#6, G#m6, G#13, G#Maj13, G#m13, A+, A7+, A#, A#m, A#7, A#M7, A#m7, A#mM7, A#6, A#m6, A#9, A#Maj9, A#m9, A#11, A#Maj11, A#m11, A#13, A#Maj13, A#m13, A#sus2, A#sus4, Bdim, Bdim7, Bm7b5,

Chords with an F#

Cdim, Cdim7, Cm7b5, C#11, C#Maj11, C#m11, C#13, C#Maj13, C#m13, C#sus4, D, D+, D7, DM7, D7+, D6, D9, DMaj9, D11, DMaj11, D13, DMaj13, D#m, D#dim, D#m7, D#dim7, D#m7b5, D#mM7, D#m6, D#m9, D#m11, D#m13, E9, EMaj9, Em9, E11, EMaj11, Em11, E13, EMaj13, Em13, Esus2, F#, F#m, F#+, F#dim, F#7, F#M7, F#m7, F#dim7, F#7+, F#m7b5, F#mM7, F#6, F#m6, F#9, F#Maj9, F#m9, F#11, F#Maj11, F#m11, F#13, F#Maj13, F#m13, F#sus2, F#sus4, GM7, GmM7, GMaj9, GMaj11, GMaj13, G#7, G#m7, G#7+, G#m7b5, G#9, G#m9, G#11, G#m11, G#13, G#m13, Adim7, A6, Am6, A13, AMaj13, Am13, A#+, A#7+, B, Bm, B7, BM7, Bm7, BmM7, B6, Bm6, B9, BMaj9, Bm9, B11, BMaj11, Bm11, B13, BMaj13, Bm13, Bsus2, Bsus4

Chords with a G

C, Cm, C7, CM7, Cm7, CmM7, C6, Cm6, C9, CMaj9, Cm9, C11, CMaj11, Cm11, C13, CMaj13, Cm13, Csus2, Csus4, C#dim, C#dim7, C#m7b5, D11, DMaj11, Dm11, D13, DMaj13, Dm13, Dsus4, D#, D#+, D#7, D#M7, D#7+, D#6, D#9, D#Maj9, D#11, D#Maj11, D#13, D#Maj13, Em, Edim, Em7, Edim7, Em7b5, EmM7, Em6, Em9, Em11, Em13, F9, FMaj9, Fm9, F11, FMaj11, Fm11, F13, FMaj13, Fm13, Fsus2, G, Gm, G+, Gdim, G7, GM7, Gm7, Gdim7, G7+, Gm7b5, GmM7, G6, Gm6, G9, GMaj9, Gm9, G11, GMaj11, Gm11, G13, GMaj13, Gm13, Gsus2, Gsus4, G#M7, G#mM7, G#Maj9, G#Maj11, G#Maj13, A7, Am7, A7+, Am7b5, A9, Am9, A11, Am11, A13, Am13, A#dim7, A#6, A#m6, A#13, A#Maj13, A#m13, B+, B7+

Chords with a G#

C+, C7+, C#, C#m, C#7, C#M7, C#m7, C#mM7, C#6, C#m6, C#9, C#Maj9, C#m9, C#11, C#Maj11, C#m11, C#13, C#Maj13, C#m13, C#sus2, C#sus4, Ddim, Ddim7, Dm7b5, D#11, D#Maj11, D#m11, D#13, D#Maj13, D#m13, D#sus4, E, E+, E7, EM7, E7+, E6, E9, EMaj9, E11, EMaj11, E13, EMaj13, Fm, Fdim, Fm7, Fdim7, Fm7b5, FmM7, Fm6, Fm9, Fm11, Fm13, F#9, F#Maj9, F#m9, F#11, F#Maj11, F#m11, F#13, F#Maj13, F#m13, F#sus2, G#, G#m, G#+, G#dim, G#7, G#M7, G#m7, G#dim7, G#7+, G#m7b5, G#mM7, G#6, G#m6, G#9, G#Maj9, G#m9, G#11, G#Maj11, G#m11, G#13, G#Maj13, G#m13, G#sus2, G#sus4, AM7, AmM7, AMaj9, AMaj11, AMaj13, A#7, A#m7, A#7+, A#m7b5, A#9, A#m9, A#11, A#m11, A#13, A#m13, Bdim7, B6, Bm6, B13, BMaj13, Bm13

Chords with an A

Cdim7, C6, Cm6, C13, CMaj13, Cm13, C#+, C#7+, D, Dm, D7, DM7, Dm7, DmM7, D6, Dm6, D9, DMaj9, Dm9, D11, DMaj11, Dm11, D13, DMaj13, Dm13, Dsus2, Dsus4, D#dim, D#dim7, D#m7b5, E11, EMaj11, Em11, E13, EMaj13, Em13, Esus4, F, F+, F7, FM7, F7+, F6, F9, FMaj9, F11, FMaj11, F13, FMaj13, F#m, F#dim, F#m7, F#dim7, F#m7b5, F#mM7, F#m6, F#m9, F#m11, F#m13, G9, GMaj9, Gm9, G11, GMaj11, Gm11, G13, GMaj13, Gm13, Gsus2, A, Am, A+, Adim, A7, AM7, Am7, Adim7, A7+, Am7b5, AmM7, A6, Am6, A9, AMaj9, Am9, A11, AMaj11, Am11, A13, AMaj13, Am13, Asus2, Asus4, A#M7, A#mM7, A#Maj9, A#Maj11, A#Maj13, B7, Bm7, B7+, Bm7b5, B9, Bm9, B11, Bm11, B13, Bm13

Chords with an A#

C7, Cm7, C7+, Cm7b5, C9, Cm9, C11, Cm11, C13, Cm13, C#dim7, C#6, C#m6, C#13, C#Maj13, C#m13, D+, D7+, D#, D#m, D#7, D#M7, D#m7, D#mM7, D#6, D#m6, D#9, D#Maj9, D#m9, D#11, D#Maj11, D#m11, D#13, D#Maj13, D#m13, D#sus2, D#sus4, Edim, Edim7, Em7b5, F11, FMaj11, Fm11, F13, FMaj13, Fm13, Fsus4, F#, F#+, F#7, F#M7, F#7+, F#6, F#9, F#Maj9, F#11, F#Maj11, F#13, F#Maj13, Gm, Gdim, Gm7, Gdim7, Gm7b5, GmM7, Gm6, Gm9, Gm11, Gm13, G#9, G#Maj9, G#m9, G#11, G#Maj11, G#m11, G#13, G#Maj13, G#m13, G#sus2, A#, A#m, A#+, A#dim, A#7, A#M7, A#m7, A#dim7, A#7+, A#m7b5, A#mM7, A#6, A#m6, A#9, A#Maj9, A#m9, A#11, A#Maj11, A#m11, A#13, A#Maj13, A#m13, A#sus2, A#sus4, BM7, BmM7, BMaj9, BMaj11, BMaj13

Chords with a B

CM7, CmM7, CMaj9, CMaj11, CMaj13, C#7, C#m7, C#7+, C#m7b5, C#9, C#m9, C#11, C#m11, C#13, C#m13, Ddim7, D6, Dm6, D13, DMaj13, Dm13, D#+, D#7+, E, Em, E7, EM7, Em7, EmM7, E6, Em6, E9, EMaj9, Em9, E11, EMaj11, Em11, E13, EMaj13, Em13, Esus2, Esus4, Fdim, Fdim7, Fm7b5, F#11, F#Maj11, F#m11, F#13, F#Maj13, F#m13, F#sus4, G, G+, G7, GM7, G7+, G6, G9, GMaj9, G11, GMaj11, G13, GMaj13, G#m, G#dim, G#m7, G#dim7, G#m7b5, G#mM7, G#m6, G#m9, G#m11, G#m13, A9, AMaj9, Am9, A11, AMaj11, Am11, A13, AMaj13, Am13, Asus2, B, Bm, B+, Bdim, B7, BM7, Bm7, Bdim7, B7+, Bm7b5, BmM7, B6, Bm6, B9, BMaj9, Bm9, B11, BMaj11, Bm11, B13, BMaj13, Bm13, Bsus2, Bsus4

Python code

The Python code for printing the list. At least Python 3.6 and 3.7 work. Use "pip install music21" to get the music21 library.

import music21

pitch_names = [
'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B']

chord_types = ['', 'm', '+', 'dim', '7',
'M7', 'm7', 'dim7', '7+', 'm7b5',
'mM7', '6', 'm6', '9', 'Maj9', 'm9',
'11', 'Maj11', 'm11', '13',
'Maj13', 'm13', 'sus2', 'sus4']

for search_pitch_name in pitch_names:
sp = music21.pitch.Pitch(search_pitch_name)
print ("Chords with a " + sp.name + ":")
for r in pitch_names: # iterate over chord roots
for t in chord_types: # and chord types
c = music21.harmony.ChordSymbol(r+t) # build a chord
# iterate over the chord's pitches
for p in c.pitches:
# if the name of the pitch or its enharmonic
# pitch is what we're looking for, print the
# chord's name
if (p.name == search_pitch_name) or
(p.getEnharmonic().name == search_pitch_name):
print (r+t, end=', ')
print ("n")

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