What is QuillBot?
QuillBot started as a paraphrasing tool in 2017 and became one of the most-used writing aids on the internet — over 50M users. They added an AI detector in 2023 to compete with GPTZero. Because their primary product is the paraphraser, the detector tends to be more lenient — they have an interest in their own paraphrased output not being flagged as AI. Free to use with no signup.
How QuillBot detects AI text
QuillBot's classifier uses what appears to be a similar perplexity + burstiness approach to GPTZero, with their own training data. They publish a confidence percentage rather than a binary verdict, which makes the detector useful as a sanity check rather than a gatekeeper. Many students use it as a quick first-check before running their work through stricter detectors.
Why most humanizers fail QuillBot
Honestly, most humanizers do not fail QuillBot — it's among the more lenient detectors. The reason humanized text occasionally still flags here is that QuillBot's detector specifically catches output from QuillBot's own paraphraser (which is widely used to rewrite ChatGPT output). If you used QuillBot to rewrite, then QuillBot detects it.
How AI Humanizer bypasses QuillBot
AI Humanizer's Standard humanizer uses a fundamentally different rewrite approach than QuillBot's paraphraser, so QuillBot does not recognize the patterns. Pass rate against QuillBot AI detector is 99%+. The included QuillBot check is a quick way to sanity-check your text before running stricter detectors.
Recommended plan: Standard humanizer (Free, Starter)
Pass rate against QuillBot: 99%. The included QuillBot detection check lets you verify before submitting anywhere.
Common mistakes that get text caught by QuillBot
- Running text through QuillBot paraphraser before AI Humanizer — QuillBot detects its own output
- Treating QuillBot as your only check — it's lenient; verify against GPTZero or Turnitin too