Most of the grammar check websites provide context around the whole webpage that helps to understand what is the "Check" button about. Because of the context of your web page is different, the label on the button should be more descriptive as well.
Based on my research, suggestions would be the following:
Check my content
Check my writing
Check your text
I would simply label the button Get recommendations because that's exactly what's happening when the user clicks on it. This way, the cognitive load is minimized and the button conveys directly what it is used for.
Generic terms like "filter" or "check" are too ambiguous and don't make it perfectly clear what will happen when the button is clicked.