GPTZero vs Turnitin vs Originality.ai: Which AI Detector Should You Trust?

GPTZero, Turnitin and Originality.ai are the three names that come up most when someone asks whether a text is AI-written. They were built for different people, and that matters more than any accuracy claim. This comparison is based on each vendor's published documentation and pricing as of October 2026; check their sites for current numbers.

GPTZero

GPTZero started as a student project in early 2023 and is now the most used standalone detector in education. It gives a document-level probability plus sentence highlighting, and its free tier is enough for occasional checks. GPTZero publishes benchmark results and is explicit that results should be reviewed by a human. Its weakness is the same as everyone's: formal human writing and short texts.

Turnitin

Turnitin's indicator is only available through institutional accounts, so it is the detector most students will actually face and the one nobody outside a school can test. It hides scores under 20% as unreliable and quotes a sub-1% document-level false-positive rate above that threshold. Read our full guide to whether Turnitin can detect AI writing.

Originality.ai

Originality.ai targets content teams who need to check freelance deliverables at scale. It bundles AI detection with plagiarism and fact-check tools, and it is widely considered the most aggressive of the three, which means more AI text caught and more human text flagged. For a publisher that is an acceptable trade; for a student accused of cheating it is not.

Which should you use?

• Teacher checking one essay: GPTZero, then talk to the student.
• Student checking your own draft before submission: GPTZero or our free AI detector for sentence highlights, knowing Turnitin may differ.
• Editor checking freelance articles: Originality.ai, with human review of anything above 50%.
• Anyone making a high-stakes decision: two detectors plus process evidence (drafts, version history).