Grammarly although supposed to be 'free' in its basic form is otherwise costly per month. For example, their Premium monthly subscription is $29.95 per month, but becomes cheaper if you 'sub quarterly


A much better one I found is British Council.org which I think will be very useful. It has rules to make 'LearnEnglish a fun and safe place to improve your English' by following their board's guidelines.

I hope this can be helpful to you.