According to ratings and reviews, the best free online grammar and spell check resource is Grammarly, which advertises the ability to catch more than 10 times the mistakes that the average word processor catches.
Grammarly is a highly touted online grammar and spell checker. It has been praised by Forbes as well as many other online sources. Grammarly features several different products, including a plagiarism checker, grammar checker, proofreading tool, and an MS Office add-on. Grammarly is free to users, but also offers three premium subscription plans, starting at approximately $30 a month, with annual plans available, as of 2015.