GPTZero is our top pick for checking whether text was written by AI, Originality.ai is best for publishers and agencies, and Copyleaks suits schools that need LMS integration and many languages. No AI detector is accurate enough to be the only evidence.
The shortlist
GPTZero
Sentence-level highlights, a usable free tier and classroom integrations.
Originality.ai
Credit-based team scanning with plagiarism and fact checks included.
Copyleaks
LMS integrations and detection across 30+ languages.
Grammarly
Shows how a document was written instead of only guessing after the fact.
Questions buyers ask
What is the most accurate AI detector?
Results vary by test. GPTZero and Originality.ai usually lead independent comparisons; Originality.ai tends to hold up better on paraphrased text and GPTZero is easier for teachers.
Can AI detectors be wrong?
Yes. All of them produce false positives, and research has found detectors over-flag writing by non-native English speakers. Use a detector score as a reason to talk, never as the only evidence.
Is there a free AI detector?
GPTZero has a free account with a monthly word allowance, and Originality.ai offers a small free allowance of daily scans.
Which AI detector is best for teachers?
GPTZero, for its sentence highlights, writing replay and Google Classroom and Canvas integrations. Copyleaks is the stronger choice when a school needs LMS-wide deployment in many languages.