QuillBot vs GPTZero: which AI detector fits your work?
QuillBot vs GPTZero is a choice between a writing suite that includes a detector and a company built around detection. QuillBot's detector scores higher on the public RAID benchmark and needs no account, but its free version stops at 1,200 words and six scans a day. GPTZero has more independent research behind it and more tools for teachers.
Our verdict: on the one shared benchmark that includes both, QuillBot comes out ahead of GPTZero. GPTZero is still the better fit for schools, thanks to Writing Replay, LMS links and a larger body of outside testing. If you already paraphrase or proofread in QuillBot, its detector is a sensible add-on; if you grade or review other people's work, start with GPTZero.
QuillBot vs GPTZero at a glance
Limits and prices as listed on each site at the time of writing (October 2026). IsThisAiWritten, our own free detector, is in the first column for comparison.
| IsThisAiWritten | QuillBot | GPTZero | |
|---|---|---|---|
| Check without an account | Yes, any length | Yes, no sign-up | Up to 10,000 characters |
| Free limit | No word limit, no daily cap | 1,200 words per scan, six scans a day | 10,000 words a month with a free account |
| Paid plan limit | No limit, free | No word limit, unlimited scans (Premium) | 300,000 or 500,000 words a month |
How the two compare on testing and features:
| QuillBot | GPTZero | |
|---|---|---|
| Minimum length | 80 words | Not stated |
| RAID, AI caught at 1% false positives | 99.2% (98.1% with attacks) | 95.7% (92.9% with attacks) |
| University studies | None found | Chicago, Maryland, Brussels |
| Languages | More than 20 | Five fully supported |
| AI-edited text | Separates AI-refined from AI-generated | Mixed AI and human detection |
| Classroom tools | No LMS integration listed | Writing Replay, Canvas, Google Classroom |
How accurate are QuillBot and GPTZero?
The RAID benchmark
RAID, presented at ACL 2024, is the only public benchmark we found with entries from both tools. It holds millions of texts across domains such as news, recipes, poetry and Reddit posts, with adversarial tricks like paraphrasing, misspellings and look-alike characters. Each team runs its own detector on the shared test set, and the maintainers score the predictions.
The strictest of RAID's headline measures is the share of AI texts caught when a detector is tuned so that only 1% of human texts are flagged. With no attacks, QuillBot's entry catches 99.2% and GPTZero's 95.7%. Across all attack types, QuillBot catches 98.1% and GPTZero 92.9%. QuillBot cites RAID on its detector page; GPTZero cites it too.
Two caveats. RAID's AI texts come from older models, such as GPT-4, Mistral and Llama chat, so the scores say little about the newest releases. And a fixed 1% threshold is a lab setting: the threshold each tool uses on its website may be different.
University studies
GPTZero has been through several recent academic tests. A University of Chicago working paper (2025) found its false positive rate steady at about 0.7%, but it missed around half or more of AI passages after a humanizer rewrote them. A University of Maryland study (2025) found the same pattern on humanized articles: 46.7% caught. A 2026 Vrije Universiteit Brussel study found it underestimated AI content in academic papers. We found no comparable university study that included QuillBot's detector, so for QuillBot, RAID is most of the outside evidence.
What the vendors say
QuillBot says its detector reaches a 99% detection rate according to RAID, and that when a result is unclear the model leans toward calling the text human to reduce false positives. It also warns that heavily paraphrased and very formulaic writing, such as legal or academic prose, is more likely to be wrongly flagged. GPTZero claims 99% accuracy on its homepage and says it retrains to keep false positives on English learners' writing at 1%.
Free limits and pricing
QuillBot's free detector needs no sign-up and allows six scans a day of up to 1,200 words each, with an 80-word minimum. Free users get one explainer card. Premium removes the word limit for detection and the daily cap, and adds full explanations and downloadable reports. Premium covers QuillBot's paraphraser, grammar checker and other tools too. When we checked from Europe, it was €8.33 a month billed yearly; the price shown depends on your region and billing period.
GPTZero lets anyone paste up to 10,000 characters without an account. A free account gives 10,000 words a month. Premium is $23.99 a month or $12.99 a month billed yearly for 300,000 words, with up to 50,000 characters per scan. Professional is $45.99 ($24.99 yearly) for 500,000 words, 150,000 characters per scan, batch uploads of 250 files and LMS integration.
For someone checking one long essay a week, GPTZero's no-account box holds more in one go. For someone checking several short pieces a day, QuillBot's six free scans may be enough.
What you see in the report
QuillBot gives a score from 0 to 100% and sorts text into AI-generated, human-written, or human-written with AI refinement, flagging specific lines. Explainer cards say why a passage was flagged. Site owners can also get a QuillBot certificate badge for human-written pages.
GPTZero separates human, AI and mixed text, highlights sentences, and offers a deeper Advanced Scan. Its Writing Replay plays back the typing history of a Google Doc, including pastes, which gives a teacher something more concrete than a score to discuss with a student.
Privacy
GPTZero's FAQ says it stores text submitted through its dashboard and uses it in aggregate to improve the service, while API submissions are not stored. It says it is SOC 2 Type II compliant. QuillBot's detector page promises a "privacy-first design" but does not state how long checked text is kept; we could not find a detector-specific retention period, so read its privacy policy before pasting anything confidential.
Who each tool suits
- QuillBot suits writers and students who already use its paraphraser or grammar checker, and anyone working in Spanish, French, Portuguese or one of its other supported languages.
- GPTZero suits teachers and schools that want detection inside Canvas or Google Classroom, plus the writing history that Writing Replay records.
A free option without a daily cap: IsThisAiWritten
If six scans a day or 1,200 words is too tight, IsThisAiWritten has no daily cap, no account and no length limit, so a full thesis goes in as one piece. It runs in your browser rather than on a server, so the text is never uploaded, and every word is scanned, never sampled. Like any detector, it can be wrong in both directions, so treat a result as a reason to look closer, not as proof. The methodology page explains how it is tested.
Where QuillBot and GPTZero are better than us: both support several languages; we are English only. GPTZero adds Writing Replay and Canvas and Google Classroom integrations, and QuillBot a full writing suite with a paraphraser and grammar checker. If you need those, use one of them, and talk to the writer before acting on any score.
Sources
- RAID benchmark leaderboard, checked October 2026
- RAID repository and submission rules, checked October 2026
- QuillBot AI Detector page and FAQ, checked October 2026
- QuillBot: 8 of the best AI detectors you can actually use for free, checked October 2026
- QuillBot Premium, checked October 2026
- GPTZero homepage, checked October 2026
- GPTZero pricing, checked October 2026
- GPTZero FAQ, checked October 2026
- GPTZero privacy and security, checked October 2026
- GPTZero: accuracy statistics, checked October 2026
- Jabarian and Imas, Artificial Writing and Automated Detection (BFI Working Paper 2025-116), checked October 2026
- Russell, Karpinska and Iyyer, University of Maryland detector study (2025), checked October 2026
- Van Vlasselaer et al., Who wrote this? (International Journal for Educational Integrity, 2026), checked October 2026
- BetaKit: Superhuman, formerly Grammarly, acquires AI detector GPTZero, checked October 2026
Questions
Are QuillBot and GPTZero owned by the same company?
No. QuillBot is a Learneo, Inc. business. GPTZero has been owned by Superhuman, the company formerly called Grammarly, since a deal announced in June 2026.
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