The Grammarly Keyboard needs full access in order to connect to the Internet. The keyboard needs an Internet connection because we use powerful servers to check your text and provide corrections. Without full access, you can still type with the keyboard, but Grammarly can’t check your grammar, punctuation, or contextual spelling.
The Grammarly Keyboard reads and corrects text only in message fields. We know that what you write on your phone is private, so we have encryption and several measures in place to make sure it stays that way.
To learn more about Apple’s full access warning, please see this article.