Review: Grammarly’s Spelling and Grammar Checker

As a writing expert who relies on Microsoft’s grammar and spelling checker to flag what I don’t see, I was eager to test Grammarly’s power to find additional errors. I signed up for the premium version and tested it to the max. I wanted to find the answer to this question: For people who already use the grammar and spelling checker in Microsoft Office, is Grammarly worth downloading in either its free or premium version? That is, does it catch issues that Microsoft misses?

My answer: yes. Grammarly catches many errors that Microsoft misses. But it also misses a few that Microsoft catches. So using both of them can result in a final version that gets close to perfect. For instance, both programs flag some but not all passive verbs. Together they flag nearly all of them. Below are the results of four tests I put both Microsoft and Grammarly through, followed by a rundown of Grammarly’s features.

Test 1:
I tested Grammarly and Microsoft on the variety of errors in my “Top 10 Writing Errors of 2015” post, errors in punctuation, grammar, sentence structure, and capitalization. In the list below, Grammarly flagged five errors: 1, 3, 4, 7, and 8. Microsoft flagged only three: 2, 7, and 10. But together they caught 8 of 10, which is a good result.

  1. Most of my correspondence is email, however, I also write reports and presentations.
  2. Thanks for your time, I appreciate it.
  3. Please feel free to contact Jesse Rosen or myself if you have questions.
  4. He is responding to a RFP from the public utility.
  5. Carmen thanks for your help with the newsletter.
  6. A last minute change in one executive’s bio delayed the proposal.
  7. When the download is complete the device automatically reboots.
  8. We are honored to have partnered with you on this important project and we look forward to our work together next year.
  9. Best Regards,
  10. Please attend the potluck for new members on January 11th.

Test 2: I tested both programs on my “Top Three Errors of 2014.” The passage below includes six intentional errors, two each in using a comma for direct address, subject-verb agreement, and using a semicolon to connect sentences using the word however. Grammarly caught five of the six errors. It missed the comma that belongs after the name Lynn. Word caught only two errors: the incorrect verb in the second sentence and the comma before however at the beginning of the second paragraph.

Lynn thank you for permitting us to reprint your recent business writing article in our newsletter. The content and your approach is extremely helpful.

I always appreciate your practical tips, however, I did not understand one of the points in a recent blog post. Why is “me” correct in the sentence “Please let Reggie and me know when you leave”? I always thought “I” was the proper pronoun, however, you indicated that “me” is correct.

Thanks Lynn. Your advice and feedback is much appreciated.

Test 3:
One of the trickiest grammar issues for grammar and spelling checkers (and human beings) is subject-verb agreement. It’s tricky because the software (and the human) has to recognize the simple subject in order to check it for agreement.

Using my blog post “Do Your Subjects and Verbs Agree?” I ran Grammarly’s software on the ten sentences below. Grammarly caught six of the ten errors: Numbers 2, 3, 5, 6, 7, and 9. Microsoft’s grammar and spelling checker also caught six errors: Numbers 3, 4, 7, 8, 9, and 10. Combined, they flagged nine of ten errors, which is an excellent result for that challenging type of error. Both Grammarly and Microsoft missed Number 1, which should be “grammar and punctuation are correct” since grammar and punctuation are two things.

  1. I want to ensure that my grammar and punctuation is correct in every document I send out.
  2. Each of the samples were labeled before shipment.
  3. Here’s three follow-up questions for you.
  4. The need to improve our processes are important to everyone involved.
  5. Testing showed that the internal temperature of these systems settle below the temperature displayed on the gauges.
  6. Clear acceptance criteria needs to be established.
  7. Proper segregation of duties do not exist between the employee performing the payroll reconciliation and the individual who updates the employee master list.
  8. The approval and the modification agreement is sent to Loan Servicing.
  9. There is not any substantial changes in any of the financial sections of this narrative.
  10. We have not determined whether Mr. Frye’s version of the events are accurate.

Test 4:
My final test was to run Microsoft and Grammarly through my Error Quests booklet of 50 short passages, each with one error. The errors are sometimes subtle, occasionally obvious. In the test, I skipped one of the 50 because I realized it is subject to interpretation. Of the other 49, Grammarly flagged 14 errors; Microsoft flagged 9. Grammarly caught two unintentional errors I had overlooked: a missing comma after the phrase “for example” and a rendering of website as web site. Thanks, Grammarly! And Microsoft caught another unintentional error: a rendering of homebuyers as home buyers. Nice catch, Microsoft!

I wish both programs did a better job of flagging frequently confused words in pairs such as complimentary/complementary, principle/principal, flush out/flesh out, discrete/discreet, and appraise/apprise. Even though a flexible human intelligence may be required to know which word or phrase fits, both programs could at least point out the potential error.

Grammarly’s premium version offers these advantages over Microsoft’s grammar and spelling checker: 

  • It works online. If you would like to check for errors in a blog post, Facebook post or comment, or another type of writing online, Grammarly will flag your errors. This great feature comes with Grammarly’s free version too, and it includes a quick synonym provider. For instance, I just double-clicked the word just, and Grammarly provided 10 synonyms for it. Easy!
  • It flags the use of the word this when it’s not clear what this refers to. Here’s an example: “This might lead to additional problems.” This what? I love this feature because I have read countless writing samples that included unclear uses of this.
  • It highlights words you use frequently and suggests synonyms. This feature is different from Microsoft’s flagging of words repeated one after another (a feature that Grammarly just added). You can also turn off this feature, which is called “vocabulary enhancement,” when you want to repeat words, as in a procedure.
  • Grammarly catches what it calls “incomplete comparisons,” things like “She skates more gracefully.” (More gracefully than whom? Than herself at an earlier time?) I like this catch because incomplete information can weaken comparisons.
  • Both premium and free versions give detailed, helpful explanations. For instance, in addition to several examples, Grammarly offered this useful paragraph to explain its reason for flagging the word but at the beginning of a sentence:

Starting a sentence with a coordinating conjunction is a matter of style and is not a grammatical error. However, many readers believe it is incorrect to do so. For very formal writing (such as a dissertation), it is best to avoid using or, and, or but at the beginning of a sentence. Often, a conjunctive adverb (such as however or nevertheless) is a good choice to transition from one sentence to another in formal writing. If not, rewrite the sentence to avoid using any conjunction.

  • Users can adjust the kinds of corrections Grammarly suggests by selecting the type of writing they are working on, with choices in general, business, academic, technical, medical, creative, and casual writing. (I didn’t test this feature, but I did observe differences between Grammarly’s suggestions for business and academic writing.)
  • Grammarly’s plagiarism check flags instances of the same text appearing on the web, and it makes suggestions for paraphrasing and citing text. I was glad to see that when I copied part of a blog post into a Word document, Grammarly flagged it and its source.

Another side of the Grammarly question involves cost. Its premium version flags over 250 types of errors and offers more services than the free version. Is it worth the current annual fee of $139.95? You need to decide for yourself. Consider these points:

  • Grammarly’s free version searches for 150 types of errors (not the full 250+) according to the company’s information.
  • Like the premium version, the free version checks for errors on the web, and it provides excellent explanations.
  • The free version does not include plagiarism checks, vocabulary enhancement suggestions, or the ability to set the type of writing (business, academic, etc.).


A Fun Feature: Both the free and premium versions send the user a weekly progress report by email. Yesterday I happily learned from that report that I write more than 99 percent of Grammarly users. Having used 2335 different words, I apparently have a larger vocabulary than 99 percent of Grammarly users too. I was more accurate than only 82 percent of Grammarly’s users last week, but Grammarly doesn’t know that sometimes I make mistakes on purpose when blogging and writing other pieces. (It’s true!)

The weekly report also lets users know about product updates. For instance, last week Grammarly added repeated words (such as “Thank you you for the gift”) to the errors it marks.

Disadvantages: When you are working in Microsoft Office, Grammarly has two disadvantages. One is that Microsoft’s auto-save feature is disabled, which means you have to remember to save your work frequently. The other is that Microsoft’s “undo” feature is disabled, which can create a disaster if you delete something by mistake. Neither of these disadvantages is a problem if you write first, then enable Grammarly. Enabling and disabling Grammarly are as easy as one click.

: I think Grammarly’s free version is well worth trying. If you like it, you may want to upgrade to get the 100+ additional error checks, plagiarism-check feature, and the ability to check for errors in different styles of writing.

I was pleased enough with Grammarly to keep using it and to become one of the company’s affiliates. You will see occasional ads for Grammarly on these pages in the future. (And I’ll be sure to check all my blog posts using the program.)

Have you used Grammarly’s grammar and spelling checker? If so, what is your view?

If you want to know when Grammarly and your grammar and spelling checker are giving you the right advice on punctuation, take my punctuation course, Punctuation for Professionals.


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By Lynn Gaertner-Johnston

Lynn Gaertner-Johnston has helped thousands of employees and managers improve their business writing skills and confidence through her company, Syntax Training. In her corporate training career of more than 20 years, she has worked with executives, engineers, scientists, sales staff, and many other professionals, helping them get their messages across with clarity and tact.

A gifted teacher, Lynn has led writing classes at more than 100 companies and organizations such as MasterCard, Microsoft, Boeing, Nintendo, REI, AARP, Ledcor, and Kaiser Permanente. Near her home in Seattle, Washington, she has taught managerial communications in the MBA programs of the University of Washington and UW Bothell. She has created a communications course, Business Writing That Builds Relationships, and provides the curriculum at no cost to college instructors.

A recognized expert in business writing etiquette, Lynn has been quoted in "The Wall Street Journal," "The Atlantic," "Vanity Fair," and other media.

Lynn sharpened her business writing skills at the University of Notre Dame, where she earned a master's degree in communication, and at Bradley University, with a bachelor's degree in English.

15 comments on “Review: Grammarly’s Spelling and Grammar Checker”

  • Lynn, very nice, thorough review. 🙂 I added Grammarly’s free version as a Firefox add-on. I always go with the free version to test it out.

    For me, it gets very annoying online as I try to write and it keeps highlighting “errors.” Yes, I do turn it off but it seems to turn back on every time I go back to Firefox. However, that could be me. 😉

    Like you, I use both Microsoft’s grammar and spelling check and Grammarly. I agree, between the two, I think you get a nice result.

    There is one odd thing I noticed online. I’m not sure if it’s WordPress or Grammarly. However, I did notice right after adding Grammarly, my posts did some wonky things (highly technical term) 😉

    For example, if I created a new paragraph in the middle of some content, it would repeat the same sentence in the original copy and in the new paragraph.

    I do think Grammarly is worth a try. I’m not convinced enough to try the premium version. But, again, that’s just me.

  • Lynn, thank you for your smart tests and thoughtful review of both Microsoft’s and Grammarly’s text-checking performance. I have used both with mixed results and, like Cathy, have had occasional “wonky” results. I agree, however, that catching some errors is preferable to missing most errors.

    My community college class ends this week, and I am eager to share your results with my writing students before they leave. I plan to offer information about this Business Writing feed and hope some of them will become new subscribers so that they can refresh their knowledge.

    Thank you for your ongoing insights and interesting blogs. Your conversational style works well, and I always look forward to seeing Business Writing appear in my email.

    Happy holidays to you and best wishes for exactly the kind of year you desire in 2017!

  • Lynn, thank you for reviewing this wonderful tool! I have been using Grammarly for over a year. I don’t know how I ever managed without it.

    I am pursuing a Master’s Degree in ministry–which is to say, I have a unique vocabulary. Still, Grammarly manages to catch many of my errors. Having said that, it’s important that a writer knows the fundamentals of the craft: Grammarly misses significant mistakes.

    I love the weekly report also: I, too, write 99 percent more than other Grammarly users (a stat that your post should change). I have a more unique vocabulary than 99 percent of users as well. Alas, my accuracy percentile is in the 80s. But, I am encouraged! One of the best features of Grammarly–both the tool and the blog–is that it provides explanations for grammatical usage.

    There’s hope for me yet!


  • Hello Cathy, Jane, and Marlene,

    Thanks for your detailed comments. I appreciate hearing about your experience with Grammarly.

    Cathy, thanks for mentioning the wonkiness. I believe I noticed the same thing–repeated text, that is–but I thought I might have copied and pasted rather than cut and pasted. Your experience suggests otherwise. My blog is hosted by Typepad, so this may be a problem across the web. I’ll watch for it happening again and will open a trouble ticket with Grammarly if it does.

    Jane, thanks for your good wishes. I am certain you are a wonderful example to your students, particularly in the way that you reach out and build relationships. I checked my email and realized I have a message from you I need to answer–from last summer! I apologize and will respond this morning.

    Marlene, my fellow 99 percenter! I wonder how many who read this blog are also in our category. I agree that Grammarly’s explanations are useful. Good luck with your program of studies!


  • Actually, I’ve been using Grammarly and Hemingway Editor free versions. But after reading your review I’m definitely gonna pay for Grammarly. It is also great that it catches plagiarism because I’ve been using separate tool ( for this and copying and pasting took some time.
    Thanks for your time, Lynn!

  • With heavy advertising, Grammarly is becoming the best-known grammar checking software. You say you tested it against Word, but don’t say which version. The latest Office 365 has a substantial revision to Word’s grammar features:

    And what about Grammarly’s many competitors, more than 20 of them. Do you know that Grammarly is truly the best?

    Thanks for looking into this.

  • Hi Thad,

    Thanks for raising those points. I tested Grammarly against Office 10 and an earlier version. My goal was to find out whether Grammarly found additional errors and was worth downloading. People will have many versions of Word–not necessarily the latest–so I wanted to know whether it offered a helpful check against what I have now.

    What Grammarly offers that Microsoft doesn’t is a check of online communications like Twitter, Facebook, etc.

    My goal was to test Grammarly, which, as you noted, is becoming the best-known grammar and spelling checker. I wanted to know whether I could stand behind it as a partner, and I found I could. If you would like to test its competitors, please do so, and give us a link to your results.

    Again, thanks for commenting.


  • Hi Lynn: Thanks for your thoughtful response.

    I am at work developing a standard test that would be usable across products. I was surprised to find (perhaps I should not have been surprised) a book on this topic, “Automated Grammatical Error Detection for Language Learners, Second Edition” ( It’s dense, though fascinating.

    I’ll let you know when I publish my results.

  • Thank you Lynn for your evaluation. I have found that Grammarly free is too limited. I use Grammarian Pro at

    Also, I’ve narrowed it down that there are really only four original grammar checkers on the web:

    Grammarian Pro –
    Ginger –

    The others are some linked form of these and most are a linked form of Grammarly’s partners/advertisements.

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