> Am I using this wrong?

Kinda. It's not a grammar corrector. The editor won't correct grammar mistakes or any "dictionarized" mistakes. It will only highklights hints for a better redability, like complex words, complex and long phrases, jargons and things like that. I think for this we have plenty of alterantives (better ones). Even the browser itself.

It works more like Hemingway App (https://hemingwayapp.com/).