Nounplus.net, Grammarcheck.net and Grammarcheck.me are free online grammar checking sites. A writer can type a thesis statement or other text into a designated area of the website and click a button to analyze it. The writer then sees highlighted mistakes or suggested changes.
Some free online grammar-checking websites also offer more in-depth analysis of text for a fee. Some sites offer writing tips and guidelines. Other free grammar-checking sites include Paperrater.com and Spellchecker.net. According to Grammarcheck.net, subject/verb agreement, misuse of commas, misuse of "which" and "that," and confusion of past and present tenses are among the most common grammatical errors.