Mandolin G chordG major: 0 0 2 3, and 5 more shapes

Frets, low course to high: 0 0 2 3 (open position)

Sounds: G D B G · G is G, B, D (1 · 3 · 5)

Found in: D major (IV), G major (I), D mixolydian (IV), G mixolydian (I), A mixolydian (♭VII), D dorian (IV)

Open courses that ring: G and D are notes of G, so they can drone under it.

No 3rd: G5 (0 5 5 3) leaves the 3rd out, so it backs G major, mixolydian, dorian and minor tunes alike.

Tuning GDAE: G D A E, low to high.

The link can’t set the tuning: the app starts on the Irish bouzouki in GDAD. Choose Mandolin once in its Settings and it remembers.

More G shapes

D major (IV, a main chord): D – G – D – A (a plain backing for many reels and jigs)
G major (I, a main chord): G – C – G – D (a plain backing for many reels and jigs)
D mixolydian (IV, a main chord): D – G – D – C (reels in D or A mix)
G mixolydian (I, a main chord): G – F – G
A mixolydian (♭VII, a main chord): A – G – A
D dorian (IV, a main chord): Dm – C – G – Dm (the major IV is the dorian colour)