QuillBot is best known as a paraphrasing tool, but it also offers a free AI detector on its website. This guide explains what the detector does, how to read its results, and how to combine it with other free tools before submission.
Try Leap's free AI tools
Leap's AI detector runs entirely in your browser. It is free, needs no signup, and nothing you paste is sent anywhere. You get a 0 to 100 score from writing signals like sentence-length variation, stock AI phrases, hedging words, and repetition, plus highlighting of the sentences that weigh most. See it in action in under a minute.If your text needs cleanup, the humanizer replaces stock AI phrases, removes em dashes and invisible characters, and adds contractions, all in the browser and free. It does not guarantee passing any detector, and no tool honestly can.
How QuillBot handles AI detection
The QuillBot AI detector accepts text through a web form and returns a percentage score plus a sentence-level breakdown. Like most detectors in this category, it looks at signals such as perplexity and burstiness, which measure how predictable and how uniform the writing is. QuillBot says its detector is also trained on output from its own paraphraser, an angle most competitors do not have because they do not own a paraphraser.QuillBot's interesting architectural choice is that it publishes the detector alongside the paraphraser, both at the top of its navigation. The company's positioning is that the paraphraser is for legitimate rewriting and the detector is for verifying originality. The practical read: if a student uses QuillBot to paraphrase AI text and then checks with QuillBot's own detector, the detector may be tuned to catch that pattern.
Accuracy in practice
QuillBot describes its detector as highly accurate but publishes less detailed methodology than some competitors, so treat any specific numbers with caution. As with every tool in this category, real-world accuracy is best on clean, unedited AI output and drops on text that has been heavily edited or paraphrased. No detector, QuillBot included, should be treated as proof on its own.False positives are a known weakness of the whole category. Research from Stanford HAI has shown that non-native English writing gets flagged at higher rates, and that caveat applies to QuillBot's detector as much as to anyone else's. A high score is a signal to look closer, not a verdict.
What to do about it
QuillBot's detector works best as one signal in a multi-tool stack rather than a standalone verdict. The common workflow: run your draft through QuillBot, Leap, and another free detector, compare the reports, and pay attention to sentences all of them flag. A sentence flagged by only one tool is probably a tool-specific artifact; sentences flagged by multiple tools are worth revising.If you used QuillBot's paraphraser on AI text, keep in mind that its own detector is trained on paraphraser output, so results on that text may differ from what other detectors report. For a final pre-submission check, running both QuillBot and Leap's in-browser detector is practical because they look at different signals and neither sees the other's report.
The responsible-use note
Defeating AI detection doesn't change the underlying integrity question. If AI help is prohibited on a specific assignment, using a humanizer to pass detection is still a policy violation, just harder to catch. This page exists to help writers understand the tooling, not to encourage misconduct. Know your institution's rules, and disclose AI use where required.If AI assistance is permitted and you just want to verify your final text reads naturally, run it through Leap's free AI detector first. If the score looks high, the humanizer can clean up stock phrases and mechanical patterns so the text reads as yours.