Does Grammarly Detect AI? Here's What We Found After Testing
Grammarly launched its own AI detection feature, but how good is it? And does using Grammarly's writing suggestions make your own text get flagged as AI-generated? We tested both questions thoroughly. Here's what students, writers, and educators need to know.
Grammarly's AI Detector: How It Works
Grammarly introduced its AI detection feature as part of its writing assistant platform. The detector analyzes submitted text and provides a percentage score indicating how likely the content is to have been generated by AI tools like ChatGPT, Claude, or Gemini.
Here's how it works:
- Sentence-level analysis: Grammarly scans each sentence and highlights passages it considers likely AI-generated.
- Overall score: You get a probability percentage (0-100%) for the entire document.
- Free tier access: The AI detector is available in Grammarly's free plan, though with some usage limits.
- Integration: It works within Grammarly's browser extension, desktop app, and web editor.
Grammarly positions its AI detector not as a "gotcha" tool but as a way for writers to check how their content might be perceived by others.
How Accurate Is Grammarly's AI Detector?
We ran a series of tests comparing Grammarly's AI detector against dedicated detection tools. Here are the results:
| Test Content | Grammarly | GPTZero | AI Detectors |
|---|---|---|---|
| Pure ChatGPT essay | 87% AI | 95% AI | 92% AI |
| Claude article | 72% AI | 88% AI | 85% AI |
| Human blog post | 12% AI | 5% AI | 8% AI |
| Human academic paper | 34% AI | 15% AI | 18% AI |
| AI + heavy editing | 45% AI | 60% AI | 55% AI |
Key takeaways from our testing:
- Grammarly correctly identifies obvious AI text but is less sensitive than dedicated detectors like GPTZero or AI Detectors.
- It has a higher false positive rate for formal/academic human writing (34% in our test vs 15-18% for dedicated tools).
- It's less reliable at detecting Claude-generated text compared to ChatGPT text.
- The results can be inconsistent—running the same text multiple times sometimes yields different scores.
Does Using Grammarly Trigger AI Detection?
This is the question that worries most students: if you use Grammarly to fix grammar and improve your writing, will AI detectors flag your work as AI-generated?
The Short Answer
Basic grammar corrections: No. Fixing typos, comma usage, and subject-verb agreement doesn't trigger AI detectors.
Grammarly's AI rewrite features: Maybe. If you use Grammarly's "improve it" or "rewrite" suggestions extensively, those AI-generated rewrites can increase your AI detection score.
The distinction is important. Grammarly now has two types of features:
- Traditional corrections (grammar, spelling, punctuation) — These make small, mechanical fixes to your text. They don't change your writing style or voice, so they won't trigger AI detectors.
- AI-powered suggestions (rewrite entire sentences, tone adjustments, "improve clarity") — These use generative AI to produce new text. If you accept many of these suggestions, chunks of your document become AI-written, and detectors may flag them.
Our advice: use Grammarly's traditional grammar checking freely. Be selective with AI rewrite suggestions, especially for academic work that will be scanned by tools like Turnitin. For more on this topic, see our guide on whether Turnitin can detect AI.
Grammarly vs Dedicated AI Detectors
How does Grammarly's AI detector stack up against tools built specifically for AI detection?
| Feature | Grammarly | Dedicated AI Detectors |
|---|---|---|
| Primary purpose | Writing assistant | AI detection |
| Detection accuracy | Good (70-85%) | Better (85-98%) |
| False positive rate | Higher (~10-15%) | Lower (~2-5%) |
| Sentence highlighting | Yes | Yes |
| Free tier | Limited scans | Varies by tool |
| Best for | Quick self-check | Serious verification |
Grammarly's AI detector is convenient if you're already using Grammarly. But for high-stakes situations—academic submissions, publishing, hiring—dedicated AI detection tools are more reliable.
Who Should Use Grammarly's AI Detector?
✅ Good For
- Writers doing a quick self-check before submitting content
- Students wanting a rough idea of how their essay might score
- Content teams doing a first-pass review of freelancer submissions
- Anyone already paying for Grammarly who wants a convenient check
❌ Not Ideal For
- Teachers making academic integrity decisions
- Publishers verifying submitted articles at scale
- Legal or compliance situations requiring high accuracy
- Detecting AI text that has been paraphrased or humanized
🔍 Need a More Accurate Check?
Our free AI detector provides sentence-level analysis with higher accuracy than Grammarly's built-in tool. No signup required.
Try Free AI Detector →Frequently Asked Questions
Does Grammarly's AI detector work on all types of text?
Grammarly's AI detector works best on English prose of 300+ words. It struggles with very short texts, code, bullet-point lists, and non-English content.
Will Grammarly Premium give better AI detection results?
Grammarly Premium offers more scans per month, but the detection model itself is the same as the free version. You're paying for higher usage limits, not better accuracy.
Can teachers tell if I used Grammarly?
Basic Grammarly grammar corrections are undetectable by AI detectors. However, if you accept Grammarly's AI-powered rewrite suggestions extensively, those sections may trigger AI detection tools like Turnitin.
Is Grammarly considered an AI writing tool?
Grammarly has evolved into a hybrid tool. Its grammar checker is traditional software, but its newer rewrite, tone, and "improve" features use generative AI. Whether using Grammarly constitutes "using AI" depends on which features you use and your institution's policies.
The Bottom Line
Grammarly does have an AI detector, and it works—sort of. It catches obvious AI text but falls short of dedicated tools in accuracy and consistency. Using Grammarly for basic grammar correction is safe, but relying heavily on its AI rewrite features could get your text flagged.
For serious AI detection needs, combine Grammarly's quick check with a dedicated AI detection tool for a more complete and reliable assessment.