Is Grammarly's AI detector free, and how accurate is it?
Yes, Grammarly's AI detector is free to use without signing up, and Grammarly says no AI detector, including its own, is 100 percent accurate. Grammarly also claims 99 percent accuracy on the RAID benchmark, which is a vendor claim. Treat the percentage as an estimate of how text reads, not a verdict.
Cite
DigiCruncher, "Is Grammarly's AI detector free, and how accurate is it?", https://digicruncher.com/topic/is-grammarlys-ai-detector-free-and-how-accurate-is-it/, accessed 2026-11-03.Is Grammarly's AI detector free, and how accurate is it? I am finishing a chapter of my thesis in civil engineering, and before I send it to my supervisor I would like to check how it might read to an AI detector. English is my second language, and an earlier paper of mine was flagged by a detector even though I wrote every sentence myself, so I am cautious.
I already use the free version of Grammarly for spelling and grammar. I saw that Grammarly has its own AI detector, but I cannot tell what is free and what needs a paid plan, and I cannot find a clear statement about how reliable it is. I do not want to pay for something that gives me a number I cannot interpret.
Which parts are free? And if it gives me a percentage, how seriously should I take it, given that my own writing has been misjudged before?
- Accepted answerNathan ColeStaffEditor, DigiCruncher ·
Yes, Grammarly's AI detector is free to use without signing up, and Grammarly says no AI detector, including its own, is 100 percent accurate. Grammarly also claims 99 percent accuracy on the RAID benchmark, which is a vendor claim. Treat the percentage as an estimate of how text reads, not a verdict.
Jae-won, here is what Grammarly's own pages say, split by what you get without paying.
Feature Free account Paid plan Paste or upload text and get a percentage score Yes, per the AI Detector page Yes Authorship tracking and shareable reports in Google Docs or Word Yes, basic tracking and unlimited reports Yes, plus detailed source attribution Share of text copied from a generative AI source Not included Included on Pro, Plus and Premium AI and plagiarism detection inside Authorship reports Not included Included on Pro, Plus and Premium AI Detector agent that shows which parts may sound AI-generated Not listed Pro, per the AI Detector page Grammarly's AI Detector (2026) returns a percentage estimate of how much text may be AI-generated and says no AI detector is 100 percent accurate.
Grammarly's Authorship help article (2026) says free accounts get basic tracking and unlimited shareable reports, while Pro, Plus and Premium add AI and plagiarism detection inside those reports.
Grammarly's Authorship help article says tracking is off by default and shows a coloured thumbprint icon once you switch it on.
For your situation Authorship may be the more useful tool. It records typing, pasting and edits in a Google Doc or Word file, so you can show how a chapter was written. It stores your text, including deleted text, for up to 10 years per the help article, so read its privacy section first.
Caveat: the 99 percent figure is the company's own claim about one benchmark, and the same page says detector results should never be relied on alone to decide whether AI was used.
Sources: Grammarly AI Detector and Introducing Authorship, Grammarly Support.
6 more replies
Most helpful first- Dana F.Member ·
Jae-won, as a teacher I worry most about the exact thing you describe, a careful second-language writer being misjudged. There is a good thread here on why detectors flag non-native English writers more often. If I ever saw a percentage on a student's paper I would treat it as a reason to talk, not a conclusion. Keeping drafts is your best protection.
- Kofi M.Member ·
One misconception I see often: people assume that if Grammarly's detector shows a low number, their instructor's detector will show the same. They are different tools with different training and different thresholds. A low score on one tells you very little about another. Ask your supervisor what they use, if anything, and what they expect on AI disclosure.
- Jae-won P.Member ·
@Nathan Cole thank you, the table is exactly what I needed. I did not realise that Authorship was a separate thing from the detector. I will turn it on for the next chapter and keep my drafts, and I will read the privacy section before I decide about my older files.
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