StealthGPT vs QuillBot: Which AI Humanizer Actually Works?
StealthGPT vs QuillBot — which AI humanizer actually delivers undetectable content? QuillBot is one of the most popular paraphrasing tools on the internet, but can its paraphraser really fool modern AI detectors? In this head-to-head comparison, we put both tools through a gauntlet of AI detection and plagiarism tests to find out which one truly works.
Table of Contents
What Is QuillBot?
QuillBot is primarily known as a paraphrasing tool. Launched in 2017, it uses AI-driven natural language processing to rephrase sentences while attempting to preserve their original meaning. Over the years, QuillBot has expanded its feature set to include a grammar checker, summarizer, citation generator, and — more recently — an AI content detector.
QuillBot offers multiple paraphrasing modes — Standard, Fluency, Formal, Simple, Creative, Expand, and Shorten — plus custom modes for premium users. The tool is widely used by students and content creators who need to rephrase text quickly.
Key distinction: QuillBot markets itself as a paraphrasing tool, not as an AI humanizer built to bypass AI detection. That difference matters, as we'll see in our tests.
What Is StealthGPT?
StealthGPT is purpose-built to do one thing exceptionally well: transform AI-generated text into content that reads as naturally human-written and bypasses AI detectors. Unlike general-purpose paraphrasers, StealthGPT's algorithms are specifically engineered to defeat detection models from Turnitin, Originality.ai, GPTZero, Copyleaks, and more.
StealthGPT also functions as an AI content generator, meaning you can produce and humanize text in a single workflow. In independent testing — including a comprehensive study comparing five leading undetectable AI tools against eight major AI detectors — StealthGPT was the only tool that bypassed every single detector.
Testing Methodology
To keep this comparison fair and transparent, we followed a strict testing protocol:
Generated a 300-word passage using ChatGPT (GPT-4) on a general knowledge topic.
Ran the raw ChatGPT text through QuillBot's paraphraser using Creative mode (the most aggressive rewriting mode available).
Ran the same raw ChatGPT text through StealthGPT's humanizer.
Submitted both outputs — plus the original ChatGPT text as a control — to 10 leading AI detectors.
Tested both outputs for plagiarism using Grammarly's plagiarism checker.
Evaluated readability using the Flesch-Kincaid readability scale.
The 10 AI Detectors Used
#Detector1Turnitin2Originality.ai3GPTZero4ZeroGPT5Copyleaks6Winston AI7Scribbr8Content at Scale9QuillBot's own AI Detector10Crossplag
We chose these detectors because they represent the full spectrum — from widely used academic tools like Turnitin to stringent commercial detectors like Originality.ai. According to research published by Stanford University's Human-Centered AI group, AI detection tools vary significantly in accuracy, making multi-detector testing essential for a meaningful comparison.
Does QuillBot Bypass AI Detectors?
After running the ChatGPT text through QuillBot's Creative mode paraphraser, we submitted the output to each of the 10 AI detectors. Here are the results:
Turnitin
Turnitin flagged QuillBot's output as 89% AI-generated. Despite the paraphrasing, Turnitin's detection model recognized the structural patterns characteristic of machine-generated text. 🔴 Verdict: FAIL
Originality.ai
Originality.ai's Turbo 3.0 model assigned a 94% AI probability to QuillBot's text. Even the Standard 2.0 model flagged 76% of the content as AI-generated. 🔴 Verdict: FAIL
GPTZero
GPTZero returned a human score of just 34%, classifying nearly all of the text as likely AI-written. 🔴 Verdict: FAIL
ZeroGPT
ZeroGPT estimated a 72.4% probability that the text was AI or GPT-generated. 🔴 Verdict: FAIL
Copyleaks
Copyleaks detected the text as AI-generated with high confidence. 🔴 Verdict: FAIL
Winston AI
Winston AI predicted a 97% chance the text was AI-generated. 🔴 Verdict: FAIL
Scribbr
Scribbr flagged 85% of the QuillBot output as AI-written. 🔴 Verdict: FAIL
Content at Scale
Content at Scale was one of only two detectors that QuillBot managed to pass, labeling the content as "likely human." 🟢 Verdict: PASS
QuillBot's AI Detector
Interestingly, QuillBot's own AI detector flagged 68% of the paraphrased text as AI-generated. That's right — QuillBot's paraphraser couldn't even bypass QuillBot's own detector. 🔴 Verdict: FAIL
Crossplag
Crossplag assigned a low AI content index, classifying the text as likely human. 🟢 Verdict: PASS
QuillBot's Final Score: 2 out of 10 — an 80% failure rate
Does StealthGPT Bypass AI Detectors?
We ran the identical ChatGPT passage through StealthGPT's humanizer and tested the output against the same 10 AI detectors.
Turnitin
Turnitin classified StealthGPT's output as 4% AI-generated — essentially identifying it as human-written. 🟢 Verdict: PASS
Originality.ai
Originality.ai's Turbo 3.0 model returned an 8% AI probability, and the Standard 2.0 model scored it at just 3%. StealthGPT comfortably cleared both models. 🟢 Verdict: PASS
GPTZero
GPTZero assigned a human score of 92%, classifying the text as predominantly human-written. 🟢 Verdict: PASS
ZeroGPT
ZeroGPT estimated only a 6.1% likelihood of AI involvement. 🟢 Verdict: PASS
Copyleaks
Copyleaks confidently classified StealthGPT's output as human-written. 🟢 Verdict: PASS
Winston AI
Winston AI gave the text a 96% human probability score. 🟢 Verdict: PASS
Scribbr
Scribbr detected only 7% potential AI content. 🟢 Verdict: PASS
Content at Scale
Content at Scale labeled the content as human-written. 🟢 Verdict: PASS
QuillBot's AI Detector
Even QuillBot's own AI detector classified StealthGPT's output as 91% human-written. 🟢 Verdict: PASS
Crossplag
Crossplag reported a 0% AI content index. 🟢 Verdict: PASS
StealthGPT's Final Score: 10 out of 10 — a perfect score ✅
Head-to-Head Results
The numbers speak for themselves. QuillBot's paraphraser was designed to rephrase text, not to defeat AI detection systems. StealthGPT was purpose-built for exactly that — and the results prove it.
Plagiarism Check
Bypassing AI detection is important, but the output also needs to be original. Plagiarized content can lead to serious academic and professional consequences. We ran both outputs through Grammarly's plagiarism checker, which cross-references billions of web pages and academic papers.
Both tools passed the plagiarism test. However, as noted by Turnitin's own research on AI writing and academic integrity, passing a plagiarism check is not the same as passing an AI detector — they measure fundamentally different things.
Readability Comparison
An AI humanizer is only useful if its output is actually readable. Some tools sacrifice coherence in the pursuit of undetectability, producing garbled sentences that make no practical sense. We compared readability using the Flesch-Kincaid readability score, where higher scores indicate easier-to-read text.
QuillBot Readability — Score: ~48 (College-level)
QuillBot's Creative mode produced reasonably readable text, but some sentences became awkward or overly convoluted after paraphrasing. The tool occasionally swapped common words for obscure synonyms, making certain passages harder to follow than the original ChatGPT output.
StealthGPT Readability — Score: ~55 (10th–12th grade)
StealthGPT's output was more accessible than QuillBot's version. Importantly, StealthGPT's text flowed naturally — sentences made logical sense, transitions were smooth, and vocabulary was appropriate without being unnecessarily complex.
While QuillBot focuses on swapping words and restructuring sentences, StealthGPT takes a more holistic approach — adjusting tone, rhythm, and sentence variety in ways that more closely mirror actual human writing patterns.
Pricing and Value
QuillBot Pricing
Free plan: Limited paraphrasing (125 words at a time), Standard and Fluency modes only
Premium: Starting at $9.95/month (billed annually) — unlocks all modes, unlimited word count, and advanced features
⚠️ QuillBot does not market or guarantee AI detection bypass as a feature
StealthGPT Pricing
Paid plans available for students, professionals, and businesses — see StealthGPT pricing
✅ Every plan includes full humanization with guaranteed AI detection bypass
The value question is simple: Would you rather pay for a paraphrasing tool that fails 80% of AI detectors, or an AI humanizer that passes 100% of them?
Conclusion
After testing both tools against 10 AI detectors, running plagiarism checks, and evaluating readability, the verdict is clear:
QuillBot is a solid paraphrasing tool for general rewriting, grammar improvement, and content refinement. But it was never designed to beat AI detectors — and our tests confirm that it doesn't. Even QuillBot's own AI detector flagged its paraphrased output as mostly AI-generated.
StealthGPT, by contrast, was built from the ground up to produce truly undetectable content. It doesn't just rephrase — it rewrites in a way that fundamentally alters the patterns AI detectors look for, all while maintaining readability and originality.
