Testing Grammarly AI Detector: Accuracy You Can Trust?

You’re probably familiar with Grammarly as a popular writing assistant, helping with grammar, style, and clarity. 

Now it also offers an AI detector—but does it really identify AI-generated text accurately? 

In this article, we’ll dive into how Grammarly’s AI detection works, test its performance, and explore what it can—and can’t—tell you about your writing. If you’ve ever wondered whether your text could be flagged as AI-generated, this guide is for you.

What Is Grammarly?

Grammarly is a popular AI-powered writing assistant used by millions of students, professionals, and businesses worldwide. It helps improve grammar, spelling, clarity, tone, and overall readability across platforms like Google Docs, Microsoft Word, email, and social media. With integrations across 500,000+ apps and websites, it has become one of the most trusted tools for writing support.

What Is a Grammarly AI Detector?

The Grammarly AI Detector is an additional feature built into the Grammarly platform that scans text to estimate how much of it may have been generated by AI tools like ChatGPT, Google Gemini, or Claude. Instead of giving only a yes-or-no result, it provides a percentage score that reflects the likelihood of AI involvement, helping writers refine their work and readers better understand its origin.

Grammarly AI Detector Key Features and How It Works

• AI Text Detection – Identifies common patterns in AI writing, such as robotic phrasing or repetitive sentence structures.

• Mixed-Content Detection – Breaks text into sections, showing which parts may have AI fingerprints.

• AI Score – Provides a clear percentage of how much text could be AI-generated.

• Supported Formats – Works with pasted text, document uploads, and through Grammarly’s integrations with apps like Google Docs, Outlook, and social platforms.

• Extra Tools – Includes grammar checks, plagiarism scanning, citation assistance, and real-time suggestions alongside AI detection.

• Multi-Language Support – Primarily English, though Grammarly works with multiple regional variations.

How Accurate Is a Grammarly AI Detector?

Grammarly promotes its AI detector as a reliable way to spot AI-written content, while also emphasizing that no AI detector is 100% accurate. According to its official claims, the tool analyzes language patterns, sentence structures, and stylistic cues to estimate what percentage of a text might be AI-generated. But how well does it work in practice? To find out, we ran a series of tests on different types of content: fully AI-written, mixed human+AI, and humanized AI text.

Test 1: Pure AI Text

Setup: For this test, we generated a passage entirely using ChatGPT-5. The goal was to see if Grammarly could correctly identify text that is 100% AI-written.

Results: Grammarly’s AI detector reported that 84% of this text appears to be AI-generated.

Observations: While the detector was directionally correct in flagging the text as mostly AI-written, it fell short of full accuracy. Ideally, a 100% AI passage should have scored close to 100%. This suggests that Grammarly tends to leave some margin of uncertainty, possibly to avoid false positives.

Test 2: Mixed AI + Human Writing

Setup: Here, we took an academic essay paragraph written by a human before the release of ChatGPT and asked ChatGPT-5 to continue it. The final text had 187 human-written words (41%) out of 454 total words.

Results: Grammarly’s AI detector marked 30% of this text as AI-generated.

Observations: This result underestimates the AI portion (59% vs. 30%), but it does reflect that the text was a mix. Grammarly seems to struggle with pinpointing the exact ratio of human vs. AI writing, though it caught the general “blended” nature of the content.

Test 3: Humanized AI Text by QuillBot

Setup: For the final test, we used QuillBot’s AI Humanizer (Basic Mode) to rewrite the fully AI-generated text from Test 1. This tool is designed to make AI text appear more natural and “human.”

Results: Grammarly’s AI detector showed that 16% of this text appears to be AI-generated.

Observations: This demonstrates how easy it can be to bypass Grammarly’s detector with humanizing tools. Despite the text being entirely AI in origin, Grammarly reported a relatively low percentage, suggesting that its system is vulnerable to sophisticated paraphrasing.

👉 In short, Grammarly’s AI detector can catch broad patterns but is far from precise. It leans conservative, often under-reporting AI content and showing vulnerability to humanized rewriting.

Grammarly AI Detector: Pros and Cons

Like many AI checkers, Grammarly’s AI Detector has strengths that make it appealing to casual users, but it also carries weaknesses that limit its reliability in professional or academic contexts. Here’s a breakdown:

Pros

• Ease of Use: The interface is clean and intuitive—just paste text or upload a file to get instant results.

• Integration with Grammarly Tools: Works seamlessly alongside Grammarly’s grammar, spelling, plagiarism, and style suggestions, which makes it convenient for students, professionals, and writers.

• Extra Features: Supports multiple formats and offers percentage scores of AI likelihood, helping writers refine their text.

• Everyday Suitability: Works reasonably well for everyday documents like emails, essays, and reports, especially when combined with Grammarly’s broader writing assistant features.

Cons

• Detection Accuracy Issues: Often underestimates or misidentifies AI content.  

• False Positives: User feedback (Quora, Reddit) notes frustration when Grammarly flagged genuine human writing as AI-generated, undermining trust.

• Lack of Transparency: Grammarly doesn’t provide detailed insights into why text is marked as AI, leaving users with unclear results.

• Login Required: Unlike some free AI detectors, Grammarly requires users to log in, which can be inconvenient.

• No Sentence-Level Analysis: The report only provides an overall score, without pinpointing specific AI-like sentences—making it hard to know where edits are needed.

• Not Ideal for High-Stakes Use: Due to false positives and bypass risks, it may not be suitable for academic or professional contexts demanding high accuracy.

👉 Overall: Grammarly AI Detector is best for casual, everyday checks where convenience matters more than precision. For strict academic or professional use, its accuracy may fall short.

Grammarly AI Checker Pricing

Grammarly provides both a free tier and a premium subscription, though the gap between them is notable.

The free tier includes the AI checker but limits submissions to about 10,000 characters each. Results are basic, offering only a percentage score without sentence-level analysis or detailed reporting. This makes it fine for short checks but less practical for essays, research papers, or larger projects.

The Pro plan, starting at $12/month, expands checks to longer documents (up to 5,000 words) and bundles the AI detector with Grammarly’s full suite of tools—plagiarism detection, sentence rewrites, and citation generation. However, the AI checker’s accuracy remains largely the same as in the free version.

Can You Bypass Grammarly AI Detector?

With the rise of AI detectors, many writers wonder whether it’s possible to bypass tools like Grammarly’s AI checker. The short answer is yes—but not with simple tricks.

Basic approaches such as synonym swapping or quick rewording are rarely effective. As shown in our Test 3 with QuillBot, even advanced paraphrasing still left the text flagged as AI-generated. These tools tend to focus only on surface-level changes, which detectors can easily recognize.

That’s why a professional humanizer is necessary. Tools like EssayDone Humanizer go beyond word substitution by restructuring sentences, varying syntax, and adding natural stylistic cues that align more closely with human writing patterns. This makes the text flow more organically while reducing detectable AI markers.

In our experiment, we ran the 100% AI-generated text from Test 1 through EssayDone Humanizer. 

The result? Grammarly’s detector reduced its AI score dramatically to 0% AI, demonstrating how deeper linguistic and structural transformations are far more effective at bypassing detection than basic rewriting.

5 Alternatives to Grammarly AI Detector

FAQ

Is Grammarly AI Detector 100% accurate?
No AI detector is fully accurate. Grammarly can indicate AI-like patterns, but it may misclassify human-written text or fail to detect subtle AI-generated content.

How to bypass Grammarly AI Detector?
Simple rewriting or word replacement is often detected. Professional humanizers, like EssayDone, restructure sentences and adjust style for more natural, human-like text.

Will my professor use an AI detector?
Some professors may use AI detection tools, but policies vary. Detectors are usually one part of evaluating originality alongside plagiarism checks and writing quality.

Can I use AI detectors on my own work before submission?
Yes. Using detectors can help you review your content and adjust AI-influenced sections before submission, but results should be interpreted cautiously.

Are AI detectors legal?
Yes. AI detection tools are legal for educational, professional, and personal use, as they analyze text patterns without violating copyright.

Is Grammarly AI Detector free?
Yes, but the free tier has a strict word limit and basic results. Premium expands word limits and adds advanced tools, but detection accuracy remains limited.

Conclusion

In this review, we explored what Grammarly AI Detector is, how it works, and its strengths and weaknesses. We also examined its accuracy through different tests, looked at pricing, and discussed possible ways to adjust AI-generated text. 

While no AI detector is perfect, understanding its features and limitations can help you make informed decisions when checking your writing. We hope this article provides useful insights and practical guidance for anyone curious about AI detection tools.