What this is actually doing.
This is the focused version of “Border radius / shape preview”: do the one job, inspect the result, and move on without opening a full editor.
Type, Layout & Effects
Border Radius / Shape Preview.
Preview a box at a chosen border radius.
1 Enter2 Adjust3 Use result
Input
Answer
464
Finished size after adding 220 on both sides
Useful for cards, buttons and image masks.
Useful to know
Four things worth knowing.
Where it stops.
It solves the named job, not every problem around it.
What to inspect.
Judge it at the size it will actually be used. Typography and spacing are partly optical.
Worth knowing.
Keep the original until the finished result has worked in the place you made it for.