An optional note is a chord tone that can be left out without changing the chord's identity. In a C7 or C9 it's usually the fifth — it sits in the middle of the chord and rarely carries the chord's character, so dropping it leaves the chord sounding like itself but lets you play it on fewer strings. Bigger chords have other optional tones depending on what's in them.

Why chords have them

Most chord names follow a recipe. A C major triad is C, E, G — root, third, fifth. A C7 adds a flat seven, so it's C, E, G, Bb. A C9 keeps going to C, E, G, Bb, D. A C13 keeps stacking from there. Each new ingredient packs more notes into a chord that still only has six strings to play with — and at some point, something has to give.

Some chord tones carry the chord's identity, and some are easier to leave out. Which is which depends on the chord:

• In seventh chords and most extensions (C7, Cmaj9, Cm9, C13, altered 9ths, and many others), the perfect fifth is usually the first to go. It fills in the harmony but rarely defines the chord once the third, seventh, and extensions are present. The exception is chords like C7b5 or C7#5 where the chord name itself alters the fifth — there the altered fifth is the chord's character, so it has to stay.
• In 11th chord families (C11, Cmaj11, Cm11), whether the third stays put depends on whether it's major or minor. On dominant and major 11ths the natural 11 sits a semitone above the major third, which sounds crowded, so the third often becomes optional (or gets pushed up to #11). On minor 11ths the minor third and the 11 are a whole tone apart — no clash — so Fretscape keeps the minor third required. Without it the chord stops sounding minor and reads more like a sus chord.
• In 13th chord families (C13, Cmaj13, Cm13), the 9th, the 11th, and the fifth can all become optional. The full stack is too tall for six strings to hold cleanly, and those middle tones are often less essential than the 3rd, 7th, and 13th.

Fretscape uses this same logic when it generates voicings. "Optional" isn't fixed to a single chord tone — it's whichever stacked note the chord type allows you to leave out, the same way a practical chord voicing would usually be built on guitar.

How Fretscape shows them

Some voicings simply don't include every chord tone — they're real, playable shapes that happen to leave an optional note out. Fretscape generates them the same way it generates every other voicing, and they show up in the results with an Incomplete tag under the diagram. It means "this voicing leaves an allowed note out", not "this voicing is wrong".

Incomplete voicings usually rank below otherwise similar complete ones, so the full-chord shapes tend to appear higher in the result list and the incompletes sit further down — there if you want them, out of the way if you don't.

Open the voicing details on any incomplete voicing and you'll see a short note saying which optional note it leaves out, and a reminder that it's still a valid way to play the chord.

Optional notes vs Omit in the builder

Two things look similar but mean different things in Fretscape:

• "Optional note" is any chord tone Fretscape may leave out automatically when it's generating voicings — the fifth on most extensions, the third on dominant and major 11ths, and the 9th, 11th, or fifth on 13ths. That's what the Incomplete tag describes — Fretscape's choice, not yours.
• "Omit" in the chord builder is a deliberate ask. You tell Fretscape to leave a specific note out of the chord, and the results update to match the new chord name. The basic OMIT row has buttons labelled 3 and 5 — tap 5 on a C9 and the chord becomes C9 omit 5, and Fretscape searches voicings of that specific chord.

See How do I add or leave a note out of a chord? for the full builder behaviour.

Optional notes vs missing notes

An optional note is a chord tone Fretscape recognises as safe to leave out for that specific chord type. The Incomplete tag marks voicings that happen to leave one out — real, playable shapes that simply don't carry every note. Voicings missing essential chord tones (the third on a plain major chord, for example) wouldn't sound like the chord, so Fretscape doesn't generate them in the first place.