At work, a few of us analyzed a new (well, it came out in 2009, so relatively new) software called Grammarly. It dubs itself “the World’s Best Grammar Checker,” and that’s fine. It may be the world’s best software grammar checker, but as I’ve said before, there is no substitute for a human editor (and I hope there never will be because a lot of us would be out of jobs).
The best thing I can say about Grammarly is that it’s thorough. It looks for all different types of errors: spelling, punctuation, misplaced modifiers, vocabulary use, and many others, even plagiarism.
However, when we looked at the errors Grammarly found versus the errors that we, as human editors, found, there were many discrepancies. The vast majority of the issues that Grammarly found were not errors. It marked prose that was perfectly fine as being wrong. It also made suggestions for word usage and pointed out passive voice and wordy sentences, but those are not errors; they’re only potential trouble spots… and subjective, depending on what kind of document is being edited and what purpose it’s for.
Grammarly did not pick up on most of the errors that the human editors found when we went through the documents. It missed some rather egregious spelling and grammar issues.
All in all, I would not recommend Grammarly unless you’re simply trying to get an idea of what kinds of issues come up in your writing a lot. Hiring a human editor would be much more worth the cost and a human editor’s feedback would be a lot more useful. These two other reviews of Grammarly are a lot more specific than mine, so if you’re interested…