AI detectors
QuillBot's AI detector: is it free, how accurate is it, and what non-native writers should know
By ESL Humanizer editorial team · Updated October 2026
Short answer
QuillBot's AI detector is free for scans of up to 1,200 words, and needs at least 80 words to give a result. Third-party tests put its accuracy at roughly 75–80%, so it gets about one text in five wrong. QuillBot itself warns against relying on AI detection alone for decisions about someone's studies or career. Schools usually run a different detector, such as Turnitin, so a QuillBot score is a self-check, not a verdict.
What QuillBot AI Detector is
A free AI detector from QuillBot, the paraphrasing and writing company, that estimates how much of a text was written or refined by AI.
| Checks for AI writing | Yes |
| Where it’s used | Mostly students and writers checking their own text |
| Free access | Free scans of up to 1,200 words; texts under 80 words can't be checked |
| Paid | QuillBot Premium removes the per-scan word limit |
How to use QuillBot AI Detector
- Open quillbot.com/ai-content-detector and paste at least 80 words — results on texts under about 200 words are less consistent.
- Run the scan to see how much of the text QuillBot attributes to AI, with the sentences it flags highlighted.
- If you used QuillBot's own paraphraser or other AI rewriting, expect those sentences to score as AI-refined.
- Treat the score as a self-check: your school most likely uses a different detector.
Want to see which of your own sentences read as AI-like, and why? Our free AI writing checker highlights the phrasing detectors react to, in your browser, without storing your text.
What QuillBot AI Detector says about itself
QuillBot warns against relying on AI detection alone for decisions that affect a person's academic standing or career. Scribbr, which belongs to the same parent company, reports 78% accuracy for QuillBot's detector in its own comparison. See QuillBot AI Detector’s website for current details.
What published tests of QuillBot AI Detector found
Third-party tests published in 2026 mostly place QuillBot's detector at about 75–80% accuracy, with formulaic academic and legal prose more likely to be wrongly flagged. Several tests are small or run by companies selling competing detectors, and none we found focused on non-native writers.
What independent research says
Vendor figures come from the vendor’s own tests. Independent research paints a more cautious picture of AI detection in general:
- In a peer-reviewed Stanford study, seven detectors misclassified an average of 61% of human-written TOEFL essays as AI-generated, while essays by US eighth-graders were classified almost perfectly (Liang et al., 2023).
- An independent test of 14 detection tools found none above 80% accuracy (Weber-Wulff et al., 2023).
- In our own October 2026 test, GPTZero flagged none of 299 scans of pre-ChatGPT student writing, learners included — but labelled all 19 learner texts that had been fully polished by AI as AI-assisted (our GPTZero study). Only GPTZero was tested, so other detectors may behave differently.
- OpenAI withdrew its own AI classifier in 2023 for low accuracy (OpenAI).
What non-native writers should know
- Using an AI paraphraser — QuillBot's included — on your own sentences can make them score as AI-refined.
- Careful, formulaic academic phrasing is a known trigger for false positives.
- Fix the specific sentences that sound generic instead of paraphrasing the whole text.
If QuillBot AI Detector flagged your work
- Check whether the flagged sentences are ones you paraphrased with an AI tool.
- Keep drafts and version history as evidence of how you wrote the work.
- Remember your school's detector may disagree — ask which tool produced any score used against you.
Need to reply in writing? Use our appeal letter template.
Wrote it yourself? Make it sound natural.
Paste a paragraph. ESL Humanizer fixes non-native phrasing, keeps your meaning and highlights every change — free for up to ~250 words.
Quick answers
Is QuillBot's AI detector accurate?
Third-party tests put it at roughly 75–80% accurate, so it misjudges about one text in five. QuillBot itself says detection shouldn't be used alone for decisions about someone's studies or career.
Is the QuillBot AI detector free?
Yes, for scans of up to 1,200 words. QuillBot Premium removes the limit. Texts under 80 words can't be checked.
Will using QuillBot's paraphraser make my writing look like AI?
It can. Detectors, including QuillBot's own, increasingly flag AI-refined text, and paraphrasing whole sentences is exactly that kind of refinement.
Do teachers use QuillBot's AI detector?
Some do, but schools more often rely on detectors built into their platforms, most commonly Turnitin. A QuillBot score won't necessarily match what your instructor sees.