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Can Grammarly Replace a Human Editor for Full Length Books?

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With the release of new writing and editing algorithms, it seems like most writers can make do without working with a human editor. Why pay someone to edit your book when you can use Grammarly?

The truth is, these AI algorithms are helpful but imperfect. As a book editor, I do use Grammarly. It helps me catch certain mistakes that the human brain doesn’t process very well. (I can get caught up in a story and forget to watch for every comma.) But there are also items that the algorithm doesn’t process well, and a trained human brain will catch easily.

Let’s run through what Grammarly is best and worst at catching in writing.

Grammarly’s Organization

Before delving into the best and worst aspects of Grammarly, it’s helpful to know how the software is organized. Edits are broken down into four categories.

  • Correctness
  • Clarity
  • Engagement
  • Delivery
  • Style Guide

When there is an error in your writing, the edits are underlined in different colors for different types of errors. Correctness is the classic proofreading red. Clarity is blue. Engagement is green, and delivery is purple. These are the main colors I see when I’m editing. I’ve actually not seen a “style guide” error because I don’t pay for that function.

Now I’ll explain how often I use each category and how helpful it is.


This category basically catches grammatical errors, like the Microsoft Word proofreading tool that has been out for ages.

It’s fabulous for:

  • Using commas appropriately
  • Pointing out incorrect verb tenses
  • Highlighting run-on sentences

It does have a few more smarts than a typical proofreading tool. Grammarly will catch words used incorrectly if they are words that are commonly confused (ex., affect versus effect).

But it’s not great at:

  • Finding misused words
  • Parsing unusual sentence structures
  • Dealing with stylistic word choices (like foreign words or colloquialisms)

As a book editor, the correctness edits are the ones that I agree with the most often. I probably accept about 80% of them. But there are always exceptions. For example, when I worked with a British author, Grammarly marked common British phrases as incorrect because I had it set to American English (for my American publisher).


As a book editor, I’m obsessed with eliminating unnecessary phrases to make reading easier. Grammarly’s clarity edits are supposed to help me make the writing clearer.

It’s pretty good at:

  • Suggesting shorter phrases to replace lengthy ones
  • Identifying which sentences are hard to read due to their length

I typically use the clarity edits to show me which sentences may be complicated for a reader to understand. Sometimes I like the alternative Grammarly gives me, and I’ll suggest it to the reader. But, often, it won’t give me a suggestion because the sentence is too complex.

So, it’s not great at:

  • Rewriting whole sentences to be shorter without changing their original meaning
  • Understanding stylistic choices

Grammarly is not as creative as the human mind, so when it suggests edits, it often suggests a simple and boring solution. If an author writes “catches her eye,” Grammarly’s suggestion of “sees quickly,” while accurate, doesn’t have the same impact.

I only accept maybe 50% of Grammarly’s clarity edits.


To be honest, I don’t usually evaluate the engagement edits when I’m editing books. Most stories meet whatever Grammarly’s threshold is for writing engaging content. Authors use unusual words, and lots of action happens.

Engagement is a useful metric when editing emails, and that’s primarily when I use it.

I may only get one or two engagement edits per book chapter, and I probably accept them about 50% of the time.


This is another metric that I associate more with emails. When I’m editing books, I’ll only get a few of these edits per chapter. They often pop up in dialogue. For example, delivery edits may suggest changing “gonna” to “going to” or tell me that I shouldn’t end a sentence in a preposition.

I probably accept these edits less than 50% of the time because they often conflict with the author’s stylistic choices. While having correct grammar is important, in many books, grammar can be second to style (as long as the sentences are still clear enough to read).

Style Guide

This tool is primarily for Grammarly business users who assign a specific style. Even though I adhere to The Chicago Manual of Style, I don’t use this function. It’s relatively easy to look up the rules and apply them to the text using my brain,


While Grammarly has many useful features to help authors hone their writing, it doesn’t fully replace a human editor. There are subtleties and stylistic choices that Grammarly just doesn’t parse well.

Of course, I’m biased because I love working as an editor.

Negotiating with writers on clarity (my primary purpose) versus style (often a writer’s primary focus) is part of the experience. We come together to create sentences that are true to the writer but also clear enough for a reader to understand.

Software doesn’t negotiate.