Criterion GPTZero Originality.ai
CategoryAI Detection & Plagiarism CheckingAI Detection & Plagiarism Checking
In one sentenceAn AI detection service that estimates whether a piece of text was written by a person, by an AI model, or by a mix of both.An AI content detector and plagiarism checker aimed at publishers, agencies, writers and educators.
Problem it solvesHelps teachers, editors and reviewers get a signal on whether submitted writing may have been produced by AI tools such as chatbots.Helps content teams and educators check whether text may be AI-generated or plagiarised before publishing or grading it.
Free planYesYes
Developer APIYes — docsYes — docs
Open sourceNoNo
PlatformsWeb, Chrome extension, Google Docs add-on, APIWeb, Chrome extension, Google Docs, Firefox, API
Pricing (summary)Free scans are available for shorter texts, with a free account needed for longer ones; paid Professional plans (monthly or annual) and Team/Enterprise plans add premium features such as advanced scans and plagiarism checks. Student and educator pricing is mentioned. Verify current plans on GPTZero's pricing page.
Checked 2026-10-13		A free Basic tier offers limited AI-detection scans per day without a subscription; paid Pro and Enterprise plans use monthly credits and add plagiarism and other checks, the Chrome extension, team features and (on Enterprise) API access, and one-time credit purchases are also available. The site says there is no free trial. Verify current plans on Originality.ai's pricing page.
Checked 2026-10-13
Strengths
  • Sentence-level highlighting shows which parts of a text drove the result
  • Fits into common education and writing workflows through Chrome, Google Docs and LMS integrations
  • Developer API with code samples in many programming languages
  • Combines AI detection, plagiarism, fact-checking and readability tools in one product
  • Team management, scan history and an API suit agencies and publishers
  • The vendor openly advises that an AI score should be one signal among several, with a human in the loop
Limitations
  • Detection results are probabilistic and can produce false positives; GPTZero's own site says no AI detector is 100% accurate and results should not be used as the final verdict or as the sole basis for academic or disciplinary decisions
  • Scores can be less reliable on short, heavily edited or mixed human/AI texts
  • Advanced features such as plagiarism checks and Writing Replay require a paid plan
  • Detection results are probabilistic and can produce false positives; Originality.ai itself says a score shouldn't be used alone for academic integrity discipline, so it should never be the sole basis for academic or disciplinary decisions
  • The free Basic tier is limited to AI detection with a small daily scan and word allowance
  • Text entered into the free tool may be used for training unless you have an account and opt out