Grammarly has a free version that will serve a writer very well. The corrections possibilities are highlighted immediately allowing you to decide if you want to make the suggested correction. The choice is important as sometimes a writer may intentionally use a misspelling such as in dialogue.
A premium version is available at a subscription fee but most writers will find the free version will serve them very well. Try the free version for a period to evaluate its value to you.
Grammarly can be downloaded at Grammarly.com