Turnitin AI Detection vs Grammarly AI Detector
Two detectors sold to different buyers, which is what actually drives the difference in how they behave on your text.
| Turnitin AI Detection | Grammarly AI Detector | |
|---|---|---|
| Built for | Universities and schools | General writers |
| Detects | text | text |
| Free tier | None. Institution-licensed only, students cannot run it themselves. | Free. |
| Vendor claim | Turnitin has publicly stated a target false-positive rate below 1% at the document level. | Cites a top placement on the independent RAID detection benchmark. |
| Main weakness | Students have no way to check their own work before submission: the biggest source of anxiety in this niche | Gives a coarse percentage with little explanation |
Which one flags more
Detectors sold to publishers (Grammarly AI Detector sits closer to this end) are tuned to reject borderline text, because a missed AI draft costs the buyer more than a wrongly rejected human one. Detectors sold into education have the opposite incentive, at least in principle, because a false accusation is a serious institutional problem.
That trade-off, not model quality, explains most of the disagreement you will see when you run the same paragraph through both.
If you are choosing one to trust
- Ask for the false-positive rate, not the accuracy figure. Accuracy hides the number that hurts people.
- Test with your own known-human writing before you rely on either.
- Never treat a single score from either as a finding of fact.