Grammarly is known for catching typos, rephrasing awkward sentences, and saving you from sending “there” instead of “their.” But now, it’s expanding into a new territory: AI detection.
In a world where tools like ChatGPT are used to write everything from emails to essays, it makes sense that a grammar tool would evolve into something that can tell the difference between human-written and machine-generated text. The real question is: does Grammarly’s AI detector actually work?
We’ve already seen other detectors on the market like CopyLeaks, GPTZero, Sapling, and so on. Some are decent. Some feel like guesswork dressed up as analysis. Grammarly’s detector is newer, but it already has one big thing going for it: trust. It’s already integrated into millions of workflows, from students to enterprise users. Adding AI detection to the mix seems like a logical next step.
But how reliable is it?
In this review, we’ll break down how the Grammarly AI detector works, who it’s for, and where it lands compared to other tools in the space.
What Is the Grammarly AI Detector?
At its core, Grammarly’s AI detector is exactly what it sounds like: a tool that scans a piece of writing and tells you whether it thinks the text was written by a human or by AI.
You paste your content into the editor, and Grammarly gives an AI likelihood score based on your input.
It’s light. It’s vague. And it’s very on-brand for Grammarly: simple, user-friendly, and built to slot into an existing workflow without overwhelming anyone.
But there’s a caveat: Grammarly isn’t positioning this as a hardcore detection tool. It’s not built for educators or institutions trying to crack down on AI misuse. It’s more of a soft awareness feature—something to nudge users into being a little more thoughtful about how their writing might come across.
Who Is It For?
If you’re a teacher or academic institution trying to enforce anti-AI policies, Grammarly’s detector probably isn’t what you’re looking for. It’s too surface-level, and it doesn’t offer the kind of depth or confidence you’d want when making a high-stakes decision.
But if you’re a writer who uses AI to assist—and you just want to make sure your content still sounds human—then this fits.
Grammarly’s AI detector is probably best for:
- Content marketers trying to avoid that “ChatGPT” tone in blog posts.
- Students who use AI tools for brainstorming but still need to hand in something that feels original.
- Professionals double-checking that AI-assisted writing doesn’t raise eyebrows.
Just remember that it’s a quick gut-check tool, and don’t treat it like a courtroom witness.
Testing Grammarly’s AI Detector
This will be in two parts: the first will use straight content from popular LLMs and the latter will be content from Undetectable AI, our favorite AI humanizer.
Grammarly vs. Gemini
Test #1
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 100%
Test #2
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 66%
Test #3
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 66%
Test #4
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 100%
Test #5
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 66%
Grammarly vs. Undetectable AI
Test #6
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 100%
Test #7
Grammarly: Successfully detected text as AI-generated.
AI Likelihood Score: 100%
Test #8
Grammarly: Classified input text as human-written.
AI Likelihood Score: 0%
Test #9
Grammarly: Classified input text as human-written.
AI Likelihood Score: 0%
Test #10
Grammarly: Classified input text as human-written.
AI Likelihood Score: 0%
Average Score
The Bottom Line
Grammarly’s AI detector is fine for what it is: a light-touch tool that gives you a quick sense of whether something feels machine-written. It works best for catching raw, unedited output from tools like ChatGPT or other mainstream generators. If someone copies and pastes directly from an AI without much cleanup, Grammarly will usually catch that.
But once things get even a little more refined—either by a human editor or a tool built for stealth—the detector starts to miss. It’s especially inconsistent when dealing with rewritten content from AI humanizers like Undetectable AI. In those cases, Grammarly either gives vague warnings or misses entirely.
Compared to more robust options like Sapling, Winston AI, or CopyLeaks, Grammarly just isn’t as reliable. It doesn’t go deep, and it doesn’t offer much transparency.
That said, if you’re already using Grammarly and just want a quick gut-check, it’s a useful add-on. Just don’t mistake it for a dedicated detection tool. It’s not there yet.
