GPTZero vs Copyleaks: Features, Accuracy and a Free Alternative

GPTZero at a glance

GPTZero was launched in January 2023 by Edward Tian, then a student at Princeton, shortly after ChatGPT's release. It became widely known for explaining its results with two ideas, perplexity (how predictable the text is to a language model) and burstiness (how much sentences vary). Its detection has since moved to more complex models, but the focus remains the same: telling human and AI writing apart, especially in education.

• Sentence-level highlighting and an overall classification (human, mixed, AI).
• A free plan with a monthly word allowance, plus paid plans for heavier use.
• Tools aimed at teachers, such as batch file checks and writing-process reports.
• A browser extension and an API for developers.

For a plain-English explanation of the signals GPTZero popularized, read Perplexity and burstiness explained.

Copyleaks at a glance

Copyleaks was founded in 2015 as a plagiarism detection company and added an AI content detector in 2023. Its strength is breadth: it combines plagiarism checking and AI detection, and it markets support for many languages and for detecting AI-generated source code.

• AI detection and plagiarism checking in one platform.
• Multilingual detection, not only English.
• Integrations with learning management systems such as Canvas, Moodle and Blackboard.
• An API and browser extension for businesses and publishers.
• Limited free scans; most features require a paid plan.

GPTZero vs Copyleaks: side-by-side comparison

Features and limits change often. Check each vendor's site for current plans before you decide.

Which is more accurate?

Both companies publish high accuracy figures measured on their own test sets. Independent evaluations paint a more cautious picture. A 2023 study in the International Journal for Educational Integrity tested 14 detection tools and concluded that none were fully accurate or reliable, with performance dropping sharply on paraphrased or edited AI text. A widely cited Stanford study the same year found that several detectors flagged essays by non-native English speakers as AI far more often than essays by native speakers.

In practice, the two tools often agree on long, unedited ChatGPT output and often disagree on short, edited, formal or mixed text. That disagreement is not a bug in one tool; it reflects how uncertain detection is in those cases.

Which one should you use?

How to compare detectors yourself

1. Pick three texts you know the origin of: one you wrote, one raw ChatGPT answer and one AI draft you edited.
2. Use at least 300 words each and the same text in every tool.
3. Run each text through GPTZero, Copyleaks and AIDetector365.
4. Note the verdict, the score and which sentences were highlighted.
5. Look at the edited draft: that is where tools differ most, and where real-world cases usually sit.

Privacy: where does your text go?

GPTZero and Copyleaks process text on their servers, and their policies describe how submissions are stored and used. Read them before uploading student work, unpublished manuscripts or confidential documents. AIDetector365 takes a different approach: the analysis runs in your browser and the text is never uploaded, which is also why it cannot offer plagiarism checking against the web.

For a wider comparison that includes Turnitin and Grammarly, see Best free AI detectors compared.

Frequently asked questions