Grammarly AI detector review
By Sourabh Singh18 September 20266 min read
A free detector inside the writing tool 229,183 keywords already point at.
Grammarly added AI detection to its free tier and instantly became one of the most-searched detectors in the market, "grammarly ai detector" alone draws around 246,000 US searches a month. It did not compete for that term so much as inherit it from an installed base of tens of millions.
What it actually does
Grammarly reports an estimated share of text that appears AI-generated, inside the editor you are already writing in. That integration is the whole value proposition: no second tab, no paste, no separate account.
Its framing is notably careful. Grammarly positions the detector as information for the writer rather than as a verdict for an assessor, and it pairs the feature with an AI humanizer that explicitly does not claim detector evasion.
Where it sits against the specialists
| Tool | Price | US visits/mo | Built for |
|---|---|---|---|
| Grammarly | Free | 14,781,728 | Writers, in-editor |
| GPTZero | Free tier | 4,517,328 | General purpose |
| Originality.ai | From ~$12.95/mo | 364,155 | Publishers |
| Copyleaks | From ~$9.99/mo | 987,521 | Institutions |
| TextAsMe | Free | New | Writers who want reasons |
How accurate is the Grammarly AI checker?
Grammarly markets its detector with a top placement on the RAID benchmark and 99% accuracy. Independent tests are less generous: one controlled study found a 78.4% true-positive rate, and reviewers report it catches raw, unedited ChatGPT output roughly 81% of the time. Like every detector, it gets much weaker once text has been edited, paraphrased or mixed with human writing.
| What you get | Grammarly AI checker (free) |
|---|---|
| Result | One percentage for the whole text |
| Sentence-level breakdown | No |
| Explanation of why | No |
| Length per check | Roughly 10,000 characters |
| Account needed | No, for a basic check |
The limitation
Like every detector here, Grammarly gives you a number and no account of what produced it. For a writer that is the least useful possible output: you learn that something is wrong without learning which sentence or which habit is responsible, so the next draft starts in exactly the same place.
It also inherits the category's false-positive problem. Grammarly is more careful than most about how it frames the result, but the underlying measurement is the same, and so is the bias against plain, even prose.
Verdict
The best detector to have running passively, because it costs nothing and is already there. Not the tool to reach for when you need to understand a flag rather than receive one.
Get the same check with the reasoning attached.
Run a free checkCommon questions
Yes. Grammarly's AI detector is free for a basic check of roughly 10,000 characters, with no account needed. It returns one percentage for the whole text.
Grammarly claims 99% accuracy on the RAID benchmark. Independent tests found lower rates, around 78 to 81 percent on unedited ChatGPT text, and accuracy drops further on edited or mixed writing.
No. They are different models. A low Grammarly score does not guarantee a low Turnitin AI score, and Turnitin's detector is only available to schools.
If you want to see which sentences are flagged and why, TextAsMe shows a score for every sentence with the reason behind each flag. GPTZero and Scribbr are other free options.
Weighing a switch? Grammarly alternatives, compared on real data
