Grammarly AI Review for 2025: Does AI Detection work on Grammarly?

Grammarly first became popular as a grammar-checking tool, with a freemium plugin helping users to refine their grammar and word choices. Overall, it can be a very useful tool for writers to strengthen the clarity of their content and help it land with their intended audience. But Grammarly has since branched out with new features focused on generative AI, with tools to automatically help "improve" and paraphrase large sections of writing, and an AI content detector.

This caused some debate among educators and students about the tool's permissibility in classes where AI usage is disallowed. Some people claim AI detectors can falsely detect Grammarly as AI if it improves one's own writing.

We will look at how the Grammarly AI content detector and actually performs against other leading AI detectors. We also check Grammarly's writing tool against GPTZero's advanced AI detector to see whether Grammarly is detected as AI, depending on the contents of its original writing.

How Does Grammarly’s AI Detector Work?

The Grammarly Detector is available as part of their plagiarism checker and can be used in their tools in Microsoft Word, Google Docs, and the Grammarly Editor. It shows a percentage score for how much of the text might be AI-generated. 

The detection model works by looking at patterns such as syntax and language structure and comparing the text to a larger dataset of both human and AI writing. While the tool is geared towards minimizing false positives, it states that it “cannot provide a definitive conclusion” and that its “AI detection score is an averaged estimate of the amount of AI-generated text that is likely contained in a given document or piece of writing.”

Key Features of Grammarly’s AI Detector

Like many other AI detection tools, Grammarly’s AI Detector homepage has a very user-friendly interface that makes it hard not to immediately understand the next steps. The simplicity makes it easy for anyone to get started straight away. 

Grammarly also has the following strengths: 

1. It bills itself as “An AI Checker From a Brand You Already Trust.” Unlike other AI detection tools, Grammarly is starting from a place of being widely known as a go-to writing assistant. This familiarity can make it an obvious choice for some users who are already familiar with the platform. 
2. It is the only AI writing partner that seamlessly integrates with 500,000+ apps and sites. This makes it easy to get real-time, strategic feedback, no matter which platform you’re writing on – whether it’s an email, or a Google Doc, or a social media post. This can be hugely valuable for students and professionals who are short on time. 
3. It promotes a Responsible AI ethos. They operate under “the belief that AI innovations should enhance people’s skills while respecting personal autonomy and amplifying the intelligence, strengths, and impact of every user”. This positions them as a company prioritizing ethical AI use. 

However, as we explore below – the main weakness it has, which overrides any of its strengths, is its consistently unreliable results when it comes to detecting what has been written by an AI tool, and what has been written by a human.

Testing Grammarly’s AI Detector Against GPTZero

We asked ChatGPT to write an essay on the history of jazz music so we could use the opening paragraph as a test. This is what it came up with:

Jazz, an influential and uniquely American art form, has a rich history that spans over a century, evolving through a dynamic fusion of cultures, styles, and innovations. Born in the heart of New Orleans in the late 19th and early 20th centuries, jazz has grown from its humble roots into a global phenomenon, influencing countless musical genres and captivating audiences worldwide. This essay explores the origins, evolution, and significance of jazz music, highlighting its enduring legacy.

We ran it through GPTZero’s advanced scan, which detects AI with 99%+ accuracy. Our result correctly labeled this as AI-generated.

This is what you would reasonably expect from a tool with this function, which gives you fairly solid confidence in its results. 

We then put the paragraph through Grammarly’s AI detector, and the major difference was impossible to ignore: it said that only 50% of this text appears to be AI-generated. 

This makes it difficult to want to use the tool, particularly if you’re a teacher or editor checking the originality of a student’s essay or a journalist’s submission. False results like this can have far-reaching consequences, like unfair punishment for students, or undermining trust in professional reputations. 

Testing Grammarly AI Writing Tools Against AI Detection

For the purposes of GPTZero's technology our team took the following stance when testing our detector with Grammarly:

• If a writer wrote an original piece of writing with their own thoughts, and then used Grammarly to rephrase, paraphrase, and improve the writing, it should still count as human.
• If a writer asks ChatGPT to generate a piece of writing, and then simply puts it through Grammarly to rephrase or paraphrase, it should still count as AI.

When interviewing educators on AI usage in their classrooms, we've learned that every teacher has a different take on whether Grammarly's AI writing features are a fair use of AI, but most agreed with this stance. Many schools are particularly worried AI detectors will falsely flag Grammarly-improved human writing as AI, but also worried students are using Grammarly to evade AI detection. We tested both cases.

Do AI Detectors catch Grammarly rewriting ChatGPT?

First, we put the same ChatGPT paragraph through Grammarly’s paraphrasing tool, which converted the original paragraph to this: 

​Jazz, a significant and distinctly American art form, boasts a rich history that stretches over a hundred years, growing through a vibrant blend of cultures, styles, and innovations. Emerging from the center of New Orleans in the late 19th and early 20th centuries, jazz has transformed from its modest beginnings into a worldwide sensation, impacting numerous musical genres and enchanting audiences around the globe. This essay examines the roots, development, and importance of jazz music, emphasizing its lasting impact.

We put this through GPTZero’s advanced scan, which again correctly flagged it with 100% probability of being AI-generated. 

While only one example, this indicates, if you're using Grammarly to paraphrase AI-generated text, advanced AI detectors like GPTZero will likely still detect it. AI-generated content is AI-generated content, and no matter how many times it has been paraphrased, it will still be caught through sophisticated AI detectors. 

Does Grammarly make AI Detectors have false positives?

We also tested the case of if human writing, paraphrased and improved by Grammarly, would suddenly falsely "turn AI," like some new stories claim. The results: no, using Grammarly on original, human writing does NOT turn your writing into AI-generated content, at least, not if you use GPTZero to detect. (We can't claim the same for other tools like TurnItIn.)

For this example, we used this writing sample that was 99% human probability with high confidence. We used Grammarly AI to paraphrase or improve each paragraph.

When tested again, the human percentage was still highly confident, 96% probability. While the percentage dropped slightly to reflect maybe some AI usage, the confidence and human categorization remained the same.

We plan to run more tests of Grammarly at scale in the future for our internal benchmarking series.

Pricing: How much does Grammarly's AI Detector cost in 2025?

Free Tier: Grammarly offers basic analysis, without the advanced tools (like detailed reports) that come with the premium version. The AI text detection submissions are also capped at 1,000 words. 

Paid tiers: While Grammarly premium plan starts at $12 a month and allows up to 5,000 words of AI text detection, even the paid version struggles to accurately identify AI-generated text in a consistent way. This makes it difficult to justify the cost on AI detection alone. 

Is Grammarly useful for improving your writing?

Grammarly as a sentence-checker can be a useful tool when it comes to gathering AI-powered feedback on your writing. It gives suggestions for improving grammar and style, which makes it valuable for all kinds of writing, from writing an academic report to a professional email. 

It can be especially useful for non-native English speakers who struggle with nuances of language. Grammarly flags obvious errors and also gives suggestions about improving overall readability, which can boost confidence and English skills. 

Final Verdict: Is Grammarly’s AI Detector worth it?

Despite its strengths, when it comes to detecting AI-generated content, Grammarly is just not that confident or reliable. In comparison to tools specifically designed for AI detection, Grammarly’s AI detection tool feels like an afterthought.

We recommend using Grammarly as a tool to improve your writing, but we don’t recommend using it as a way to detect whether or not a piece has been written by AI.

We also don’t recommend using its paraphrasing tool on AI-generated writing; it won't bypass GPTZero's detector, which is used by more than 6 million people worldwide.

Better tools exist and specialize in AI detection and writing feedback. Platforms like GPTZero provide more advanced detection features which in turn deliver way more consistently accurate results, and writing feedback aimed at teaching you how to improve your writing.