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 only reads and corrects the text you type while using it. This means that Grammarly does not see information from any of your other keyboards, including the default keyboard for iOS. We know that what you write on your phone is private, so we have encryption and several other measures in place to make sure it stays that way.
To learn more about Apple’s full access warning, please see this article.