Repeat text
A string, repeated, with something between the copies if you want it. The limit is a hundred thousand characters and it says so rather than hanging. Nothing you type here leaves your browser. It is worked out on your own device, so there is nothing to send and nothing to log — which matters more for text than for most things, because people paste in work they are not supposed to paste anywhere.
There is a limit, and it is stated
This stops at a hundred thousand characters. Not because anything breaks at a hundred thousand and one, but because a repeat box with no limit is a way to hang a browser tab by typing a large number into it, and a tool that freezes without saying why is worse than one that refuses.
The limit is on the output rather than the count, so repeating one character a hundred thousand times is allowed and repeating a paragraph a thousand times may not be.
What this is actually for
Test data, mostly. A field that should reject long input needs long input to reject. A layout that has to cope with a wall of text needs a wall of text.
It is also the quickest way to build a separator line, or to check that something which claims to handle a hundred rows handles a hundred rows.