Grammarly AI Checker Review: Is It Accurate?

In August 2024, Grammarly launched its AI content detector after calling AI checkers “unreliable.”

Grammarly is trusted by over 30 million people around the world. 

It is well-known for helping with spelling, grammar, style, and tone on many devices and platforms. 

Because of this, people were excited when Grammarly added a tool to detect AI-written content.

Now we have to check, do AI Checker of Grammarly solve the problems they once criticized?

Is Grammarly AI checker accurate?

Or we’ll be specific.

Is Grammarly AI checker reliable?

In this blog, we’ll test Grammarly’s AI checker across six different content types to see how well it actually works.

We’ll show you exactly where it succeeds, where it fails, and whether you can trust it for your content verification needs. 

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Key Takeaways

• Grammarly’s AI checker achieved only 33% accuracy in our tests across 6 types of content.

• The tool correctly identified 100% human content but failed to detect fully AI-generated text.

• Is Grammarly AI checker accurate? Based on our testing, the detector struggles with paraphrased AI content and mixed human-AI writing.

• Free users have a limit of 1,000 words per submission, whereas premium users have higher limits.

• More specialized tools like Undetectable AI’s detector (100% accuracy) are much more reliable than the Grammarly AI checker free version.

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What Is the Grammarly AI Checker?

Grammarly AI Checker is designed to help you spot whether a piece of writing might have been generated by AI. 

The detector is built right into Grammarly’s existing platform, so it works alongside their grammar, spelling and style tools. 

Here’s how Grammarly AI checker rollout went:

• August 2024: Official launch of the AI detector
• September 2024: Beta version released for Google Docs
• Early 2025: More features on the way, especially for educators

This feature is a part of Grammarly’s broader push for “Grammarly Authorship.” It’s their way of taking a stand for authentic, human writing in an age where AI is everywhere.

Who is this tool for?

• Students and teachers.
• Content creators and marketers.
• Professional writers.

Since the detector is part of Grammarly’s main platform, it’s much easier to use than separate AI-checking tools. 

If you’re already using Grammarly, this feature fits right into your workflow—no need to copy and paste into another website.

Key Features of Grammarly’s AI Detector

Here are the standout features of Grammarly AI checker:

• Grammarly AI checker free plan analyzes up to 1,000 words. Premium offers higher limits and more tools.

• Fully embedded in Grammarly’s web, desktop, and mobile apps—no extra tools needed.

• Shows a percentage likelihood of AI-generated content.

• Works on browser extensions, desktop apps, and mobile devices.

• Detects AI content instantly as you write.

How Grammarly’s AI Checker Works

Grammarly AI checker work by spotting patterns that are common in AI-written content. 

It looks at things like how sentences are built, the style of writing, and repeated language structures.

The tool uses machine learning. 

That means it has been trained on lots of examples to recognize what AI writing usually looks like. 

Grammarly says they use “rigorous testing” to make sure the tool is directionally accurate—good at spotting likely AI, even if not perfect.

But how reliable is Grammarly AI checker performance in practice? It works best with longer texts.

Short passages don’t give it enough data to analyze, so the results may be less accurate.

Because it’s built into Grammarly’s platform, it also uses the same systems that check grammar and style. 

This helps it understand the overall flow of your writing. 

But there’s a downside—since it’s not a dedicated AI detector, it may miss things that specialized tools are better at catching.

Is Grammarly AI Checker Accurate?

To evaluate Grammarly AI checker is accurate or not, we used ZDNet’s framework.

This methodology analyzes six distinct content categories to measure real-world performance.

The Test: 6 Categories of Content

We tested the AI checker Grammarly provides against six types of content:

Category	Content Type
1	100% AI
2	100% Human
3	Lightly Edited AI
4	Paraphrased AI
5	Mixed Human + AI
6	AI with Plagiarism

Let’s see how Grammarly AI checker performed under each category:

Category 1: 100% AI

Reality: Fully AI-generated
Grammarly Result: 50% AI
Verdict: Incorrect Detection

This content was generated entirely by ChatGPT with zero human editing.

The AI Grammarly checker should have flagged this as highly AI-generated, but it only detected 50% AI probability.

Category 2: 100% Human (Classic Advertisement)

Reality: Human-written
Grammarly Result: 0% AI (100% Human)
Verdict: Correct Detection

The content was written decades before AI tools existed. The Grammarly AI checker correctly identified this as entirely human-written.

Category 3: Lightly Edited AI

Reality: Primarily AI with minimal human edits
Grammarly Result: 25% AI
Verdict: Incorrect Detection

Only 20-25% of this content received human editing. The AI checker Grammarly significantly underestimated the AI involvement.

Category 4: Paraphrased AI Content

Reality: AI origin, paraphrased to sound human
Grammarly Result: 33% AI
Verdict: Correct Detection

This content was originally AI-generated, then paraphrased using humanization tools. The Grammarly AI checker detected some AI traces.

Category 5: Mixed Human + AI Content

Reality: 50% human writing + 50% AI-generated phrases
Grammarly Result: 20% AI
Verdict: Incorrect Detection

With equal parts human and AI content, the AI Grammarly checker should have detected around 50% AI involvement, not 20%.

Category 6: AI with Plagiarism

Reality: AI-written with factual historical overlap
Grammarly Result: 25% AI
Verdict: Incorrect Detection

This was fully AI-generated content that happened to include some historically accurate information. The Grammarly AI checker missed the AI generation entirely.

Final Scorecard

Out of 6 total test cases:

• Correct Detections: 2 (Categories 2 and partially 4)
• False Positives/Negatives: 4 (Categories 1, 3, 5, 6)

Detection Accuracy: 33%

The Grammarly AI checker shows limited reliability, accurately identifying content only one-third of the time.

While it excels at recognizing purely human content, it consistently underestimates AI involvement across all other categories.

This performance highlights a critical issue: the AI checker Grammarly isn’t just unreliable—it’s dangerously misleading for users who need accurate AI detection.

So for your own content verification… 

Use Undetectable AI Detector to get 100% accurate results. In ZDNet’s own testing, this AI detector has correctly identified all six categories without false positives and negatives.

You can also apply our Undetectable AI Humanizer to rewrite any flagged sections until they appear genuinely human.

Re-test with multiple detectors to confirm your content passes across different platforms

Grammarly AI Checker Weaknesses and Limitations

Here are the main ways Grammarly’s AI checker doesn’t quite hit the mark:

Accuracy Issues

• It sometimes overlooks content that is clearly written by AI.
• When it gives low AI scores, it can make you think the content is more original than it really is.
• The results are not consistent – accuracy changes based on the type of content and which AI model created it.

Technical Limitations

• Free users can only scan up to 1,000 words at a time.
• It’s optimized for English and doesn’t handle other languages well.
• Casual, creative, or informal writing can confuse it.
• It tends to slow down when analyzing longer texts.

Practical Drawbacks

• You can’t upload or check multiple documents in one go.
• It doesn’t differentiate between AI-edited and AI-written content.

Core Challenges

• The tool is struggling to keep pace with how quickly AI is evolving.
• Newer AI models can easily slip past its detection.
• Mixed content—where humans edit or expand on AI output—often flies under the radar.

Grammarly AI Checker vs. Other AI Detectors

When it comes to AI detection accuracy, Grammarly’s AI checker struggles to keep up with tools specifically designed for this task.

Here’s how the top detectors performed in our testing:

Tool	Accuracy	Standout Feature	Weakness	Price/Month
Grammarly	33%	Seamless integration with writing platform	Dangerously low accuracy rates	$12
Undetectable AI	100%	AI humanizer to bypass detectors	Limited free usage	$19
Copyleaks	50-80%	Multilingual support (30+ languages)	Less precise with newer AI models	$17
GPT Zero	100%	Sentence-by-sentence AI probability scoring	Limited free tier	$15
StealthWriter AI	50%	Rewrites AI text to appear human-written	May alter original meaning	$20

Note: We’ve conducted comprehensive reviews of both Copyleaks and StealthWriter AI using the same testing methodology.

Can Grammarly Detect AI-Edited or Paraphrased Text?

This is where the AI checker Grammarly shows its biggest weaknesses.

Paraphrased AI Content Performance

In our testing, Grammarly AI Checker detected only 33% AI in content that was originally 100% AI-generated but paraphrased using humanization tools.

This means that anyone using AI paraphrasing tools or AI humanizer software can easily bypass Grammarly AI Checker detection.

AI-Edited Content Challenges

The AI Grammarly checker struggles even more with AI-edited content—text that starts human but receives AI enhancement or expansion.

Our “lightly edited AI” category showed only 25% AI detection when the reality was 75-80% AI involvement.

Tools like Undetectable AI’s humanizer and AI paraphraser are specifically designed to evade detection. In our last review, we tested the accuracy of the humanizer tools, and our testing showed:

StealthWriter AI: Reduced AI detection from 100% to 5% across multiple detectors.
Undetectable AI: Achieved 1% AI detection after humanization
Quillbot Paraphrasing: Still showed 76% AI detection (less effective)

The Bottom Line: If someone wants to bypass Grammarly AI Checker, readily available tools make it trivially easy.

Access our AI Detector and Humanizer directly through the widget below.

FAQs About Grammarly AI Checker

Conclusion

The Grammarly AI checker is easy to use because it’s built into the Grammarly platform, but our tests show that it’s not very accurate. 

It was accurate 33% of the time. This means it frequently misses AI-generated content or gives incorrect results.

So, is the Grammarly AI checker accurate enough? 

If you just need a quick and simple check inside Grammarly, it might work. 

If you truly need to determine whether something was written by AI, this tool alone isn’t sufficient—there are other options that perform much better.

The free version of the Grammarly AI checker lets you check short texts, and the paid version gives more features—but neither one fixes the accuracy problem. 

If you need to trust the results, it’s better to use reliable tools like Undetectable AI Detector for 100% accuracy.