Does Grammarly Detect AI? Grammarly's AI Checker Explained
People ask this two ways: does the Grammarly app flag AI writing while I edit, and does Grammarly sell a standalone AI detector I can check text with? The answer to both is yes, but the second one is newer and weaker than the dedicated tools, and the first one barely touches your text at all. Here is the honest split.
Grammarly the editor does not flag your AI text
The Grammarly writing assistant you use in your browser and docs is a grammar, clarity and tone tool. It will smooth stiff phrasing and reduce repetition, which incidentally makes text read less robotic, but it does not run an AI-detection scan and it will not warn you that a passage looks machine-written. If you are hoping Grammarly silently protects you from a detector, it does not work that way. It is an editing layer, the same category as a humanizer, not a detector.
Grammarly also ships a separate AI detector
Separate from the editor, Grammarly offers an AI text checker you can paste text into for a percentage. It exists because the question 'is this AI' became unavoidable in schools and workplaces, and Grammarly folded an answer into the brand people already trust. As of 2026 it is free to use for a basic check, with limits on length, and it returns a single overall score rather than sentence-level detail.
How accurate that detector actually is
Independent testing places Grammarly's detector in the middle of the pack rather than at the top. On unedited model output it catches a decent share of AI text, but its false-positive rate is higher than GPTZero's and it offers none of the sentence-level explanation that makes a flag reviewable. For a quick ballpark read it is acceptable; for any decision about a student or a client's work, the dedicated detectors remain the safer call.
The false-positive trap still applies
Because Grammarly's detector, like every other, reads statistical smoothness, it misflags careful and non-native writing more often. ZeroGPT shows the same weakness at scale, with false-positive rates measured between 15% and 33% and a heavy misflag rate on ESL writers. A single bare percentage from any of these tools, with no sentence-level reasoning behind it, is exactly the kind of number that should never stand alone as a verdict.
Cross-check before you trust it
If you run text through Grammarly's checker, verify with an independent engine before acting. Originality.ai is the publisher's pick for edited drafts because it holds up on paraphrased text where lighter checkers crumble, and Scribbr is the student-side pick because it explains its flags in plain language. Two detectors that disagree tell you the text sits in genuinely ambiguous territory; one bare score tells you almost nothing.
When Grammarly is the right tool anyway
For most people the useful Grammarly is still the editor, not the detector. Smoothing awkward AI phrasing where you already write, without leaving the app, quietly reduces the most obvious tells, and paired with a careful read it improves prose more durably than chasing a score. Use the detector only as a free first pass, and never as the final word on whether something was written by a human.
Bottom line
Grammarly the editor does not detect AI; a separate Grammarly AI checker does, but it lands mid-pack on accuracy with a higher false-positive rate than GPTZero and no sentence-level explanation. Use it only as a free first pass, cross-check with a dedicated detector like Originality.ai or Scribbr before any consequential call, and remember the editor itself is an editing layer, not a verdict.