The safe zone that keeps it from being cropped
X’s large image card has a 2:1 ratio, while 1200×630 px is about 1.91:1, so a little of the top and bottom edges can be cropped. This tool leaves a margin of about 12% at the top and bottom, so the title, logo and footer text stay intact on every platform. For X, you can also choose a 1200×600 px size.
A long title is shrunk automatically until it fits in four lines. If it still does not fit, the title is cut off with “…” and you are told. A short, clear title is always easier to read on a phone screen.