An open string left ringing against a fretted grip. Because it costs no finger, it sounds a note the closed shape has none left for -- a tension on top, or a pedal root underneath. Either a familiar grip with open strings added, or a shape so sparse the open strings carry the chord. These belong to their key rather than to a shape, so D, A, G and E have many and Eb a handful.
Fdim7 is F, Ab, Cb and D — Fdim with a diminished seventh stacked on top.
It sounds suspenseful and rootless. Three stacked minor thirds divide the octave evenly, so the same four notes spell four dim7 chords and the shape repeats every three frets.

| F | Ab | Cb | D |
|---|---|---|---|
| 1 | ♭3 | ♭5 | ♭♭7 |
Leading-tone or passing chord — it can resolve almost anywhere.
Also written F°7, Fo7 or F diminished 7. The same chord either way; which spelling you meet depends on who wrote the chart.
An open string left ringing against a fretted grip. It costs no finger, so it can sound a note the closed shape has none left for: a tension on top, or a pedal root underneath.
These belong to their key rather than to a shape: they cannot be moved up the neck. D, A, G and E have many; E♭ has a handful.
Fdim7 has 6 of them, on strings 6-5-4-3-2-1, strings 5-4-3-2-1 and strings 6-4-3-2-1, from the 3rd fret up to the 6th — every inversion the chord has: Ab in the bass, Cb in the bass and Ebb in the bass. The one to learn first is the Ab shape at the 3rd fret, which is the easiest grip here.
Start with xx3434 — no barre and low, at the 3rd fret. 1 of the 8 shapes here sits in open position. 4 of the 8 need a barre. Together they cover the neck from the 1st fret to the 15th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| 1x0101 | open position | F, root position | F | barred |
| 123131 | 1st fret | F, root position | F | barred |
| xx3434 | 3rd fret | F, root position | Ab | all fretted |
| xx6767 | 6th fret | Ab, 1st inversion | Cb | all fretted |
| x89797 | 7th fret | F, root position | Cb | all fretted |
| x-x-9-10-9-10 | 9th fret | Cb, 2nd inversion | D | all fretted |
| 13-x-12-13-12-13 | 12th fret | F, root position | F | barred |
| 13-14-15-13-15-13 | 13th fret | F, root position | F | barred |
The same notes rebuilt from scratch give 5 shell, 15 drop 2 and 10 drop 3 voicings, each on its own page.
Tensions. A shell of Fdim7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (G), the 11 (Bb), the b13 (Db) and the maj7 (E).
A diminished seventh divides the octave evenly, so Fdim7 has no single root and no single destination: it can lead to Bb or to Gb, and it is the same four notes either way.
Every note of Fdim7 is in F diminished and F half-whole diminished.
Change one note of Fdim7 and you have Fdim (drop the sixth), Fm6 (the flat fifth becomes a fifth), Fm7b5 (the sixth becomes a flat seventh) or FmMaj7b5 (the sixth becomes a major seventh).
Fdim7 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Fdim7’s sound and use this page follows Stefan Kostka, Dorothy Payne & Byron Almén, Tonal Harmony (McGraw-Hill, 8th ed., 2018). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.