GPTZero vs Copyleaks: AI detector comparison
A side by side look at pricing, methodology, language support and best-fit use case. Every claim on this page is linked to a source at the bottom.
Last updated . Reviewed by IsItAI Editorial.
At a glance
GPTZero
US, 2023The original AI detector, popular with educators in the US.
- Pricing
- From $14.99/month (Essential)
- Free tier
- 10k words/month free
- API
- Yes
- Languages
- 7
Copyleaks
Israel, 2015Enterprise-grade detection with multilingual support.
- Pricing
- From $9.99/month (100 credits)
- Free tier
- Limited free credits
- API
- Yes
- Languages
- 30
Side by side
| Feature | GPTZero | Copyleaks |
|---|---|---|
| Free tier | 10k words/month free | Limited free credits |
| Starting price | From $14.99/month (Essential) | From $9.99/month (100 credits) |
| Cost per 1k words | $0.02 on Pro plan | $0.10 |
| API available | Yes | Yes |
| Languages supported | 7 | 30 |
| Founded | 2023 | 2015 |
| Country | US | Israel |
| Primary audience | US schools and universities | Enterprises and institutions |
| Best for | US educators familiar with the brand and its 'perplexity and burstiness' explanation | Enterprise teams needing multilingual detection and integrations |
| Known weakness | Documented false-positive issues on non-native English writing in peer-reviewed studies | Pricier than competitors for low-volume users |
How each tool works
GPTZero
Method: Perplexity and burstiness analysis on a sentence-by-sentence basis. Founded by Edward Tian.
Data handling: US hosted. Stores submissions for model improvement unless on enterprise plan.
Copyleaks
Method: Proprietary classifier with paraphrasing-resistance claims. Integrates with LMS and CMS platforms.
Data handling: Enterprise tier offers no-storage option. Default plan stores submissions.
How accurate are AI detectors? What the research says
Two findings from independent academic research apply to almost every detector on this list, including GPTZero and Copyleaks.
1. False positives on non-native English writers. Liang et al. (Stanford, 2023) found that GPT detectors flagged over half of TOEFL essays written by non-native English speakers as AI-generated, while flagging almost none of the essays from US students. If your use case involves non-native English writers, never treat a detector verdict as proof on its own.
2. Paraphrasing reliably defeats classifiers. Sadasivan et al. (Maryland, 2023) showed that running AI output through a paraphraser drops detection performance close to chance. Both GPTZero and Copyleaks are vulnerable to this.
For a deeper breakdown of how accuracy claims hold up across 2026 testing, see our guide to how accurate AI detectors actually are in 2026.
Where GPTZero wins
- Free tier at 10,000 words per month. Copyleaks offers only limited free credits.
- Publicly documented methodology based on perplexity and burstiness, widely discussed in academic literature.
- Lower per-1,000-word cost at $0.02 on the Pro plan versus $0.10 for Copyleaks.
Where Copyleaks wins
- Multilingual detection across 30 languages versus 7. Required for international institutions and enterprise teams.
- Native LMS and CMS integrations alongside an enterprise no-storage tier for sensitive submissions.
- Paraphrasing-resistance claims built into the classifier. GPTZero's statistical features are more susceptible to paraphrasing attacks (Sadasivan et al. 2023).
Which one should you pick, GPTZero or Copyleaks?
Pick GPTZero if you are a US educator who needs a free tier, a transparent methodology, and a low per-word cost. Pick Copyleaks if you are an enterprise or international institution that needs multilingual coverage, platform integrations, or a documented no-storage option. GPTZero has documented false-positive issues with non-native English writing (Liang et al. Stanford 2023), so do not use either tool as definitive proof.
Frequently asked questions
Is GPTZero free?
10k words/month free
Is Copyleaks free?
Limited free credits
Can either tool be fooled by paraphrasing?
Yes. Sadasivan et al. (2023) demonstrated that paraphrasing reliably defeats most AI classifiers. Treat any detector verdict as a screening signal, not proof.
Are AI detectors fair to non-native English writers?
Independent research (Liang et al. 2023) found high false-positive rates for non-native English writing. Always combine a detector signal with other evidence, never use it as a sole basis for an academic or hiring decision.
Which one should I pick if I have to choose one, GPTZero or Copyleaks?
Pick GPTZero if you are a US educator who needs a free tier, a transparent methodology, and a low per-word cost. Pick Copyleaks if you are an enterprise or international institution that needs multilingual coverage, platform integrations, or a documented no-storage option. GPTZero has documented false-positive issues with non-native English writing (Liang et al. Stanford 2023), so do not use either tool as definitive proof.
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Sources and further reading
- GPTZero homepage
- GPTZero pricing
- Liang et al. (Stanford, 2023): GPT detectors are biased against non-native English writers
- Copyleaks AI content detector
- Copyleaks pricing
- Sadasivan et al. (2023): Can AI-generated text be reliably detected?