QuillBot AI Detector vs Grammarly AI Detector: 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
QuillBot AI Detector
US, 2017 (AI detector 2023)Free detector from the company best known for paraphrasing tools.
- Pricing
- Free (Premium suite from $9.95/month)
- Free tier
- Free unlimited
- API
- No
- Languages
- 3
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
Side by side
| Feature | QuillBot AI Detector | Grammarly AI Detector |
|---|---|---|
| Free tier | Free unlimited | Free tier with limits |
| Starting price | Free (Premium suite from $9.95/month) | Bundled in Grammarly Pro from $12/month |
| Cost per 1k words | Free | Bundled |
| API available | No | No |
| Languages supported | 3 | 1 |
| Founded | 2017 (AI detector 2023) | 2009 (AI detector 2024) |
| Country | US | US |
| Primary audience | Students and casual writers | Existing Grammarly users |
| Best for | Quick free checks alongside QuillBot's paraphraser | Existing Grammarly users wanting a one-click sanity check |
| Known weakness | Conflict of interest. The same company sells the paraphraser that defeats detectors | English only and not the main product |
How each tool works
QuillBot AI Detector
Method: Free classifier within the QuillBot writing suite.
Data handling: Stores submissions for product improvement.
Grammarly AI Detector
Method: Detector added 2024 inside the Grammarly editor. English only.
Data handling: Stores submissions per Grammarly's main privacy policy.
How accurate are AI detectors? What the research says
Two findings from independent academic research apply to almost every detector on this list, including QuillBot AI Detector and Grammarly AI Detector.
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 QuillBot AI Detector and Grammarly AI Detector are vulnerable to this.
Where QuillBot AI Detector wins
- Free unlimited checks where Grammarly's free tier is limited and the detector sits behind Pro at $12/month.
- Multilingual coverage across 3 languages. Grammarly's detector is English only.
- Pairs naturally with QuillBot's paraphraser if you are testing whether content gets flagged.
Where Grammarly AI Detector wins
- Detector lives inside an editor most knowledge workers already use, so no new tool to learn.
- Tighter integration with grammar and clarity feedback for everyday writing.
- Stronger brand trust with corporate procurement than a paraphraser company.
Which one should you pick, QuillBot AI Detector or Grammarly AI Detector?
Pick QuillBot if you want a free unlimited detector and you are comfortable with the conflict-of-interest fact that the same company sells the paraphraser that defeats AI detectors. Pick Grammarly if you already pay for Pro and want everything in one editor. Neither is suitable as primary evidence in academic or hiring decisions.
Frequently asked questions
Is QuillBot AI Detector free?
Free unlimited
Is Grammarly AI Detector free?
Free tier with limits
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, QuillBot AI Detector or Grammarly AI Detector?
Pick QuillBot if you want a free unlimited detector and you are comfortable with the conflict-of-interest fact that the same company sells the paraphraser that defeats AI detectors. Pick Grammarly if you already pay for Pro and want everything in one editor. Neither is suitable as primary evidence in academic or hiring decisions.
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Sources and further reading
- QuillBot AI detector
- Sadasivan et al. (2023): Can AI-generated text be reliably detected?
- Grammarly AI checker
- Liang et al. (Stanford, 2023): GPT detectors are biased against non-native English writers