Grammarly or ChatGPT?

A year or two ago, I compared both these AI tools. Now ChatGPT has changed a lot since 2023, and so has Grammarly. In this updated comparison, I’m putting both to the test so you can see what’s best for fixing your work and pressing publish.

Let’s start with pricing. You can use Grammarly for free, but to access its AI tools for grammar checking and content generation, you’ll soon upgrade to Grammarly Pro (previously Premium). That costs $12 per month if you pay annually, or $30 monthly for short-term projects.

With Grammarly Pro, you can rewrite full sentences at a click, adjust writing tone, get personalized suggestions, detect plagiarism, and generate text with AI.

Similarly, while ChatGPT offers a free version, you’ll need ChatGPT Plus ($20 monthly) to access its latest reasoning models. Interestingly, Grammarly Pro connects to OpenAI and ChatGPT models, so you’re getting some ChatGPT capabilities with your Grammarly subscription.

For this comparison, I used ChatGPT–4.0—it’s fastest for written content and questions. I’ve found ChatGPT–4.5 quickly hits usage caps, which is why I focused on 4.0.

I write and send a daily email to my list, around 500–600 words, which I create quickly. For testing, I copied my daily email into both tools—using Grammarly’s web app (though you could use their browser plugin).

Grammarly flags grammar and spelling errors under the correctness report, highlighted in red. Examples included missing apostrophes, typos, and hyphenation issues. As I click on each issue, I can see suggested fixes in the sidebar.

For ChatGPT, I used this prompt: “Analyze this email for grammar mistakes, typos, spelling errors, and identify potential writing style and tone improvements.”

While ChatGPT identified many issues, making fixes with Grammarly is faster—I can accept multiple suggestions at once via the sidebar. With ChatGPT, I must copy text and manually apply fixes in my writing app.

After comparing both tools’ suggestions, ChatGPT missed several errors that Grammarly caught. If I need to publish quickly, Grammarly wins on efficiency.

Grammarly’s reports are comprehensive: correctness for spelling/grammar, clarity for sentence structure, and engagement/delivery for tone and quality. I particularly like the readability report—the easier content is to read, the better.

ChatGPT can provide readability scores when prompted, but requires repeated prompting for suggestions on fixing sentence structure and vocabulary. In Grammarly, these are available with a single click.

As an Irish writer, I use British English spelling. Grammarly lets me switch between language variants (American, British, Canadian, Australian, Indian).

ChatGPT doesn’t offer this functionality without specific prompting.

Grammarly’s generative AI feature is particularly useful for improving written content. I can highlight text, click “Write with generative AI,” and choose options like “improve,” “simplify,” “make assertive,” or “detail.” Each generates variants I can insert with one click.

While ChatGPT can perform similar functions with the right prompts, Grammarly’s pre-built options are more convenient. Both tools generate comparable content—likely because Grammarly uses ChatGPT’s model.

Both check for plagiarism effectively. I tested them with an article from my site, and both correctly identified the source. However, they only work for content freely available online, not material from books or behind paywalls.

They can also detect AI-generated content. I created text with ChatGPT, and both tools flagged it as AI-written, with Grammarly even offering citation options.

ChatGPT’s newer Projects feature lets me create a project for my newsletter, upload examples readers responded well to, and add instructions for tone and style. Grammarly lacks this functionality—you train it through dictionaries and document-specific prompting.

Grammarly’s app actions are convenient for quick responses across the web. For example, if someone pitches me about dropping a link on my website, I can click the Grammarly icon and select “write a rejection email” to generate a response with adjustable tone.

Additionally, Grammarly offers a custom dictionary for words you don’t want flagged and version control for retrieving older document versions. ChatGPT requires scrolling through chat history to find previous versions.

My takeaway? Use Grammarly if you write or publish frequently, need quick grammar and spelling fixes, want help with proofreading and plagiarism detection, or find its AI writing assistant saves time.

Use ChatGPT to generate content, brainstorm, and handle other tasks Grammarly can’t do. That’s why I subscribe to both—Grammarly helps me fix content and publish quickly, while ChatGPT helps me ideate and develop topics.

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