Is grammarly not correct here?

If my plugin Passwordly, only sends the keystrokes inside password boxes, is or isn't that a key logger? It's only capturing a subset of your input, like Grammarly, so not a keylogger?

If the argument is, it's not a keylogger because it's not logging sensitive information, well I type plenty of sensitive information into non-password textboxes.

I’d say passwordly also isn’t a key logger. By your definition every text editor would be a key logger. That may be the strict definition of a key logger but the commonly accepted meaning is different. A keylogger logs all keys regardless of the app being used or general use case. Often they are malicious as well but that doesn’t have to be the case.