Grammarly AI Detector vs GPTZero: 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
Grammarly AI Detector
US, 2009 (AI detector 2024)Detection layered onto Grammarly's writing assistant.
- Pricing
- Bundled in Grammarly Pro from $12/month
- Free tier
- Free tier with limits
- API
- No
- Languages
- 1
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
Side by side
| Feature | Grammarly AI Detector | GPTZero |
|---|---|---|
| Free tier | Free tier with limits | 10k words/month free |
| Starting price | Bundled in Grammarly Pro from $12/month | From $14.99/month (Essential) |
| Cost per 1k words | Bundled | $0.02 on Pro plan |
| API available | No | Yes |
| Languages supported | 1 | 7 |
| Founded | 2009 (AI detector 2024) | 2023 |
| Country | US | US |
| Primary audience | Existing Grammarly users | US schools and universities |
| Best for | Existing Grammarly users wanting a one-click sanity check | US educators familiar with the brand and its 'perplexity and burstiness' explanation |
| Known weakness | English only and not the main product | Documented false-positive issues on non-native English writing in peer-reviewed studies |
How each tool works
Grammarly AI Detector
Method: Detector added 2024 inside the Grammarly editor. English only.
Data handling: Stores submissions per Grammarly's main privacy policy.
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.
How accurate are AI detectors? What the research says
Two findings from independent academic research apply to almost every detector on this list, including Grammarly AI Detector and GPTZero.
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 Grammarly AI Detector and GPTZero 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 Grammarly AI Detector wins
- Detection is built into the editor, so no separate tool to open for users already working in Grammarly.
- Grammarly Pro at $12/month bundles grammar, style, and AI detection. GPTZero Essential at $14.99/month covers AI detection only.
- Stronger brand recognition in corporate procurement environments, with Grammarly founded in 2009 versus GPTZero in 2023.
Where GPTZero wins
- Free tier at 10,000 words per month. Grammarly's free tier is limited and the AI detector sits behind a Pro subscription.
- API access for teams building detection into automated pipelines. Grammarly has no public API for its AI detector.
- Supports 7 languages versus 1. Non-English documents cannot be checked using Grammarly's detector at all.
Which one should you pick, Grammarly AI Detector or GPTZero?
Pick Grammarly if you already pay for Pro and want a quick in-editor sanity check without switching to a separate tool. Pick GPTZero if you need a free dedicated detector, API access, or support for languages beyond English. GPTZero has documented false-positive issues on non-native English writing (Liang et al. Stanford 2023), so treat both tools as a screening aid rather than conclusive evidence.
Frequently asked questions
Is Grammarly AI Detector free?
Free tier with limits
Is GPTZero free?
10k words/month free
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, Grammarly AI Detector or GPTZero?
Pick Grammarly if you already pay for Pro and want a quick in-editor sanity check without switching to a separate tool. Pick GPTZero if you need a free dedicated detector, API access, or support for languages beyond English. GPTZero has documented false-positive issues on non-native English writing (Liang et al. Stanford 2023), so treat both tools as a screening aid rather than conclusive evidence.
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Sources and further reading
- Grammarly AI checker
- GPTZero homepage
- GPTZero pricing
- Liang et al. (Stanford, 2023): GPT detectors are biased against non-native English writers
- Sadasivan et al. (2023): Can AI-generated text be reliably detected?