Aside from the fact that it does not work on this web page, It is far from bulletproof and could conceivably cause problems for people learning the language. It is likely to cause people to click on selections without understanding the reason, which means that many people will learn nothing from using it, and become zombies. For example, it says that "in Facebook" is incorrect, and that I should use "on Facebook"., but when I use "in a browser" Grammarly does not tell me to use "on a browser". The reason it gives is that "It appears that the preposition in may be incorrect or unnecessary in this context. Consider changing or removing it." However, Grammarly says "preposition" should be "proposition" (incorrect) so you need to be careful when using this app.