QuillBot AI Detector Review: Accuracy Tested With Real Samples

QuillBot’s AI detector is one of the most-used free options out there, as it has been bundled right into a web utility that millions already use for paraphrasing. And that popularity alone makes one question worth answering properly:

Does it actually work, or does it just look convincing?

To find out, we tested it ourselves through four scenarios that mirror how people actually use it—with raw AI text, AI text edited by a human, writing that’s 100% human-made, and human writing that’s had AI touch up the grammar, flow, and clarity. And what follows is a breakdown of how the QuillBot AI detector handled each scenario.

So, with that in mind, let’s begin!

Our Quick Verdict
The QuillBot AI detector nailed ‘raw, unedited AI text’ with a perfect ‘100% score.’ But the moment editing entered the picture, the results got inconsistent—a ‘30–40% human rewrite’ cut the AI score to ‘34%,’ a ‘fully human-written piece’ still picked up a small ‘5% false positive,’ and simply ‘running clean human writing through ChatGPT for grammar fixes’ pushed the ‘AI score’ up to ‘41%.’ So, it is a solid tool for catching obvious, untouched AI content, but it’s not reliable enough to be the final word on anything edited, refined, or borderline.

Below, we break down exactly how the AI detector of QuillBot performed in each scenario, where it held up, where it fell apart, and whether it’s worth adding to your workflow or not.

What Is QuillBot AI Detector? — A Complete Overview

The AI detector of QuillBot is a free feature built into this web utility’s writing suite. You paste in your text, hit the ‘Detect AI’ button, and get a probability score in seconds—without needing an account for basic use.

What sets the QuillBot AI detector apart from a simple yes/no checker is its four-way classification system:

It sorts text into categories, such as content that appears entirely machine-written, AI-written text that was later refined by AI, and human-written drafts that were edited by AI.

And that distinction matters a lot.

But how?

Well, a blog post that started as a ChatGPT draft and was then heavily rewritten by a human editor is a very different case than a raw, unedited AI dump—and QuillBot is one of the few free tools that tries to tell the two apart.

But one detail worth noting upfront is as follows:

And that’s a rare acceptance from a company selling AI detectors, as it says something about how QuillBot itself views its AI detector.

So, it frames how you should treat every AI score it gives you.

Our Testing Approach

Instead of relying only on secondhand claims, we ran the QuillBot AI detector through four hands-on tests that were specifically designed to mirror how people actually use AI text checkers:

1) Raw AI-Generated Text

Here, we generated a 300-word sample by an LLM—ChatGPT in our case—and submitted it to QuillBot without any modifications.

2) AI Text With Human Editing

In this, we took the same ‘Test # 1’ sample and naturally rewrote 30–40% of its content as human writers, while retaining much of the original AI-generated content.

3) AI Draft Completely Rewritten by a Human

Here, we completely rewrote the ‘Test # 1’ sample from scratch, as a human writer. And to do so, we used the AI output only as the initial draft/reference. We then included our own perspective, judgment, relevant expertise, examples, and other original insights.

4) Human-Written Text Refined by AI

Here, we took the completely rewritten human version from ‘Test # 3’ and passed it through an LLM or AI writing assistant only for grammar, clarity, and flow improvements. We didn’t ask the AI model to generate new ideas or substantially rewrite the content.

Results From Our Testing Process

Test # 1

To test the QuillBot AI detector, we’ve started the proceedings with the following text sample:

So, upon running this output as-is in QuillBot’s AI detector, we’ve got the following result:

As you can see, this tool has generated a ‘100% likely AI-generated score’ for a text piece that has been fully AI-generated. So, it works perfectly fine in such situations.

Test # 2

But now, let’s kick things up a notch!

Let’s rewrite 30-40% of the above AI-generated text sample as a human writer and see what happens.

So, upon doing so, here is the version that we’ve got:

Now, if you compare this version with the previous (fully) AI-generated one, you will realize that it has been edited by 30-40%. So, upon scanning it with QuillBot AI detector, we’ve got the following output:

As you can see, the percentage of ‘AI-generated’ text has significantly dropped from ‘100%’ to ‘34% ’. And the ‘Human-written’ label is now showcasing a ‘66%’ score. So, that’s a major change, considering that we’ve only:

• Changed the wording here and there.
• Made some structural modifications.

and

• Added one or two sentences.

And this is something that’s definitely worth noticing.

Test # 3

Now, let’s fully rewrite this short article using our own style and see what happens then.

So, upon doing so, we’ve ended up creating the following version:

And when we ran it through the AI detector of QuillBot, we got the following report:

Gleaning from above, the fully human-written version still has a ‘5%’ likelihood of being ‘AI-generated.’ So, that’s definitely a false positive because if you compare the text used in ‘Test # 3’ with the earlier two versions, you will realize how different it looks.

But that false positive is understandable, considering that QuillBot itself states that its AI detector just gives a likelihood; it doesn’t generate final proof.

Test # 4

As promised, in this test, we’re going to ask AI (ChatGPT) to modify our written version for clarity, flow, and grammatical improvements. So, when we prompted AI, this is the output we’ve got:

And here is how the QuillBot AI detector has analyzed this text:

As you can see, the AI report now claims that ‘41%’ of the text is ‘AI-generated’ and ‘59%’ of the content is ‘Human-written.’ So, the score has definitely changed, which means that while refining content, ChatGPT may have introduced some patterns that AI text generators usually use to generate content.

Where QuillBot AI Detector Struggles

Our four tests turned up some real cracks, and they’re worth calling out honestly:

1) False Positives Do Happen, Even if They’re Small

The ‘Test # 3’ flagged a piece we wrote entirely in our own words as ‘5% AI-generated.’

Now, that’s a minor number, but it’s not zero—and it’s a good reminder that no AI detector, including this one, should be treated as final proof.

2) Grammar-Only AI Edits Can Spike the AI Score in a Big Way

In ‘Test # 4,’ our fully human-written article jumped from a ‘5%’ to a ‘41%’ AI-generated score after we only asked ChatGPT to fix its grammar and flow—no new ideas, no rewritten structure, nothing substantial changed.

Now, that’s a massive swing for such a small edit, and it means that writers who use AI purely to proofread their own work could end up unfairly flagged.

3) Light Human Editing Can Mask Heavy AI Origin

In ‘Test # 2,’ reworking just 30–40% of a fully AI-generated draft dropped the AI score from ‘100%’ all the way down to ‘34% ’.

Now, that’s genuinely useful if you’re actually editing your own AI-assisted draft. However, it also shows how easily the QuillBot AI detector can be fooled by anyone who is trying to sneak AI content past it with a light pass.

4) Short Text Still Isn’t Its Strong Suit

Every sample we tested ran 300+ words. But independent research consistently shows that AI detectors, including this one from QuillBot, get far less reliable once a text piece drops below roughly 80 words.

5) The ‘Human-Written & AI-Refined’ Category Almost Never Fires

Across all four tests—including the ‘Test # 4,’ which was built specifically to trigger it—this category stayed stuck at ‘0%.’ So, even though QuillBot markets a three-way breakdown, in practice, the tool leans almost entirely on a simple ‘AI%’ vs. ‘human%’ split.

Where the AI Detector of QuillBot Actually Works Well

To be fair, the results weren’t all bad from the QuillBot AI detector. In fact, a few things genuinely impressed us:

1) It Actually Responds to Real Editing, Not Just Guesswork

The drop from ‘100%’ to ‘34%’ in ‘Test # 2’ shows that the score genuinely shifts based on how much of the text has been reworked, rather than spitting out a static or random number, regardless of input.

2) It’s Free, Fast, and Doesn’t Gate You Behind a Signup

You get a full breakdown—AI-generated, AI-refined, and human-written percentages, plus sentence-level highlights—in seconds. All that without the need to create an account.

3) It Mostly Gets Fully Human Writing Right

A ‘5% AI score’ in ‘Test # 3,’ on a piece that started life as an AI draft but was completely rewritten in our own words, is close enough to accurate to count as a pass.

4) It Nails Raw, Untouched AI Text

The ‘Test # 1’ returned a full 100% AI-generated score on an unedited AI sample, with ‘0%’ attributed to human writing. So, that’s about as clean and confident a result as any detector, free or paid, is going to give you. 

So, Is the QuillBot AI Detector Worth Using?

Well, yes, but you should treat it as a first-pass check, not a final verdict.

That’s because our own testing backs this up pretty clearly. The AI detector of QuillBot nailed the easiest case—100% on raw, untouched AI text—and did a reasonable job on genuinely human writing, too, with only a small 5% false positive in ‘Test # 3.’ So, that’s the kind of performance that makes it a handy, free addition to your writing toolkit.

But the moment editing enters the picture, things get shakier:

• A 30–40% human rewrite was enough to cut the AI score by two-thirds in ‘Test # 2.’
• And in ‘Test # 4,’ simply running clean, human-written text through ChatGPT for grammar fixes pushed the AI-generated score up to ‘41%’—even though nothing about the actual content or ideas had changed.

So, if you’re using QuillBot AI detector to sanity-check your own writing before submitting it somewhere, then it’s a solid free option. But if the result is going to decide a grade, a job, or a client relationship, then don’t stop at QuillBot’s score alone—and don’t forget that QuillBot itself says the same thing.

Some Frequently Asked Questions (FAQs)

Can QuillBot detect text written by ChatGPT specifically?

Yes, at least when the text is unedited. Our ‘Test # 1’ sample was ChatGPT-generated and untouched, and QuillBot flagged it as 100% AI-generated. However, it doesn’t tell you which AI model was used; it just showcases how likely the text is to be AI-generated overall.

Can QuillBot AI detector wrongly flag human-written content as AI?

Yes, it can. A piece we wrote entirely ourselves still came back with a small 5% AI-generated score. More notably, a genuinely human-written piece jumped to a 41% AI score after we ran it through ChatGPT for grammar fixes alone—even though no ideas or structure changed.

Does paraphrasing or light editing help text bypass QuillBot’s AI detector?

To some extent, yes—and that’s one of the bigger concerns from our testing. Editing just 30–40% of a fully AI-generated draft dropped the AI score from 100% to 34%. And this means that a fairly light human pass can meaningfully lower the detected AI percentage.

Is the QuillBot AI detector accurate?

It depends entirely on the text. On raw, untouched AI writing, our test returned a perfect 100% score. But accuracy dropped once editing was involved. So, it is accurate for the obvious cases, less so for anything in between.

Is the QuillBot AI detector free to use?

Yes. A basic scan is free and doesn’t require creating an account.

Should I trust the QuillBot AI detector for academic or professional submissions?

You can use it as a quick self-check, not final proof. Our testing showed that it can both under- and over-flag content depending on how it’s been edited—and QuillBot’s own product page advises against relying on any single detector for decisions that affect someone’s career or academic standing.

Will QuillBot’s AI detector match what Turnitin or my school shows?

Not necessarily. The AI detector of QuillBot is a separate, independent tool from Turnitin and other institutional detectors. Each uses its own model and scoring method. Therefore, a score from QuillBot won’t necessarily match what your school’s system reports.