guitar chord
F♯dim7
Three minor thirds stacked. The seventh is doubly diminished, which is why it is written with a double flat.
Written the other way round it is G♭dim7 — the same twelve keys on a piano, a different piece of notation.
Every fingering that fits a hand
20121x
moderate
20454x
hard
234242
hard · barre
2312xx
hard
23424x
hard · barre
What is true of it
F♯dim7 is F♯, A, C and E♭ — 1, b3, b5 and bb7 counted from F♯.
The easiest of the 5 fingerings below is 20121x: 4 fingers, held at the 1st fret.
None of them uses an open string, so this chord moves up the neck unchanged — the same shape 1 fret higher is the chord a semitone above.
2 of the 5 need a barre.
1 string stays silent.
Where its notes are on the neck
The brass dots are F♯, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
F♯dim7/A
x01212
F♯dim7/C
x3424x
F♯dim7/E♭
xx1212
An inversion is the same chord with a different note lowest. The name changes to a slash name because the bass is what a listener hears as the foundation.