What it does
Zakef Gadol ("large upright") is the standalone version of Zakef Katan. Where Zakef Katan needs a Munach in front of it to feel complete, Zakef Gadol does the same disjunctive job on its own. Function is identical; the melody and notation differ slightly.
Where it appears
Less common than its smaller cousin. Used when the word that would carry the Zakef has no preceding servant word in the phrase, so the trope itself takes on the longer melody to compensate.
How to remember it
Same upright dots as Zakef Katan, but with a small vertical line beside them, the "gadol" or "big" version. A useful rule: if you see a Zakef without a Munach in front of it, expect it to be Zakef Gadol.
Example from the Torah
Bereishis 28:16
In this verse, Yaakov's declaration "Hashem is in this place" opens with Zakef Gadol on יֵ֣שׁ, standing alone without a servant trope leading into it.
Hear the melody
A synthesized rendering of the melodic shape, not a vocal recording. For a baal koreh's voice on a full aliyah, PocketTorah is a great free resource.
Hand signal (simanim)
Often confused with
Both have two vertical dots above the letter. Zakef Gadol adds a small vertical line. Use the "is there a Munach before it?" test to distinguish in practice.