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Chord substitution tool for guitarists

Your progression works but sounds flat? The chord substitution tool takes one chord and suggests the chords that can replace or set it up, grouped by colour, with diagrams showing how to play them. It also suggests modulations to other keys, with the pivot chords that get you there.

With Premium, or as a one-off module.

Try it free

What the tool suggests

Type a chord (G7, Dm7, Cmaj7, C…) and click "Suggest". Each suggestion is a card: the original chord crossed out, the replacement chord, its category (diatonic, dominant, modal, chromatic, jazz), an explanation and a strength / usage meter out of 5. Under each card, diagrams show how to play the new chord, as fingerings or as degrees.

For G7, for example, you get:

Suggestion	Technique
C#7 (Db7)	tritone substitution
C#7#11	tritone sub with #11
Dm7 then G7	split into a ii-V
D7	secondary dominant (V7 of G)
G#dim7	passing diminished

For a major chord such as C, the list changes: relative minor Am7, mediant Em7, secondary dominant G7, C#dim7, borrowed Fm, G#maj7 (Abmaj7) and A# (Bb), plus the backdoor dominant A#7 (Bb7). The tool spells notes with sharps: read Db7 for C#7 if your key uses flats.

The theory in practice: why these chords work

A substitution keeps the chord's function (rest, preparation, tension) while changing its colour.

Tritone substitution: G7 (G B D F) and Db7 (Db F Ab Cb) share their third and seventh, B and F. Play Dm7 (x-5-x-5-6-x), Db7 (x-4-x-4-6-x), Cmaj7 (x-3-x-4-5-x): the bass walks down D, Db, C; the C of Dm7 slips to B (G string, 4th fret), which holds through Cmaj7, and F (B string, 6th fret) falls to E (5th fret).
Secondary dominant: any chord can be preceded by its own V7. In C, Am, Dm, G7, swap Am for A7: the C# in A7 pulls up to the D of Dm.
Modal interchange: you borrow a chord from the parallel mode. In C, F, Fm, C, the Ab of Fm (borrowed from C minor) falls to the G of C. It never fails.
Passing diminished: C, C#dim7, Dm7 raises the bass by a half step on every chord.

Note that substitutions are computed from the chord you enter. Borrowed chords and the backdoor dominant treat that chord as a tonic: enter your I chord to see what the key can borrow.

Modulations: changing key cleanly

Below the substitutions, the tool lists possible modulations from the key set in "Key (context)", major or minor. Each card gives the new key, an explanation, the pivot chords to play and a transition fluidity meter.

From C major, for example:

to G (the dominant): D7 then Gmaj7, very smooth;
to F (the subdominant): C7 then Fmaj7;
to the relative minor Am: Bm7b5, E7, Am7;
to D (a whole step up): A7 then D, the classic last-chorus lift.

A panel sums up the method: find a pivot chord common to both keys, set up the new tonic with its V7 (or ii-V7), then stay on the new I for a few bars. For an abrupt half-step or whole-step lift, you need no pivot: the jolt is the point.

Access: Premium or a 6.90 € module

Chord substitutions is part of the GuitarHarmony workshop (app.guitar-harmony.com). You need a free account to open the workshop, but this tool is locked on the free plan. To use it:

Premium, 4.90 € a month or 39 € a year, which also unlocks every other tool and unlimited AI analysis;
or the Chord substitutions module, 6.90 € paid once, lifetime access, no subscription.

To practise spotting these substitutions for free, the "Substitution challenge" in the fretboard games quizzes you on tritone subs, relative keys and secondary dominants (3 sessions a day on the free plan).

How to use it

Pick the chord to substitute. Type the chord in the field (G7 by default) and click "Suggest". If the symbol is not recognised, the tool asks you to try G7, Dm7 or Cmaj7.
Set the key context. Under "Key (context)", click the tonic (C, C#, D, Eb…) then "Major" or "Minor". This setting drives the modulations listed further down.
Compare the cards. Suggestions are sorted from most common to most colourful. Read the category, the explanation and the meter, then switch the diagrams between Fingering (finger numbers) and Degrees (1, 3, 5, 7).
Try it in your progression. Play the original progression, then swap a single chord for the suggestion. One substitution per phrase is often enough. Then scroll down to the modulations to plan a key change with the pivot chords.

What you can do with it

Making a ii-V-I sound jazzier

A first reharmonization to try: in Dm7, G7, Cmaj7, replace G7 with Db7. The bass moves chromatically and the guide tones stay put. Add the #11 version for a more modern colour.

Adding colour to a pop song

In C, Am, F, G, replace the second F with Fm, or set up Am with E7. Two small changes and the chorus gains emotion without touching the melody.

Preparing a key change

To end a song in C a whole step higher, the tool suggests A7 then D. Play A7 in the last bar before the final chorus and the new key arrives naturally.

Frequently asked questions

What is a tritone substitution?

It means replacing a dominant seventh chord with the one a tritone away, for example G7 with Db7. Both chords share their third and seventh (B and F), so the tension stays the same, but the bass now falls by a half step to the tonic.

Is the chord substitution tool free?

No. It needs Premium (4.90 € a month or 39 € a year) or the Chord substitutions module, a one-off 6.90 € purchase with lifetime access. Your GuitarHarmony account stays free for the other tools.

Why does it write C#7 instead of Db7?

Chord names are displayed with sharps. C#7 and Db7 are the same chord (enharmonic spellings). In a flat key such as F or Bb, write Db7 on your chart.

Does it analyse my whole progression?

No, it works on one chord at a time. To analyse a full progression, with key, Roman numerals and reharmonizations, use the AI chord progression analysis.