HumanFlow is not one of the two tools on this page. We sell a rewriter and run a detector of our own, so weigh this accordingly — our methodology sets out how we source what appears below and what we refuse to claim.
These are not competitors. Scribbr and QuillBot are both owned by Learneo, Inc. — which is the single most useful thing to know before reading either company's comparison of AI detectors.
Last reviewed 16 August 2026 · The HumanFlow team
Both are free, both require no payment to run a check, and both turn up in the same search results for people who want a second opinion without buying anything. So they get compared as alternatives, which is a reasonable thing to do right up to the moment you learn they are corporate siblings.
The comparison is also where a widely circulated ranking comes from. Scribbr publishes a test of AI detectors that is quoted across the web as though it were independent, and in it Scribbr and QuillBot take the top three positions. That is not a scandal on its own — but a reader deciding between these two on the strength of that page should know who wrote it.
There is a fair objection to this page that should be stated before the argument rather than after it: we sell a rewriting tool and QuillBot sells a rewriting tool, so we compete with one of the two products discussed here. Our assessment of QuillBot's detector is nonetheless more favourable than of Scribbr's, on the grounds that it discloses its threshold direction and its known weaknesses. Read that in light of the conflict and check the linked sources.
No prices. Neither of these is a tool most readers choose on cost, and for one of them there is no public price at all — detector pricing, where it could be captured, is on our detector pricing page.
| Dimension | Scribbr | QuillBot |
|---|---|---|
| Who it is sold to | Consumers, free. Owned by Learneo, Inc., which also owns QuillBot, Course Hero, CliffsNotes, LitCharts, Symbolab, Bartleby and LanguageTool. | Consumers. The detector is free; the paraphrasing suite is the product. Owned by Learneo, Inc., the same parent as Scribbr. |
| How you get at it | Unlimited checks, no sign-up, capped at 1,200 words per submission. | Free on its site, with no published scan cap. |
| What it needs | 1,200 words per submission on the free detector. | A minimum of 80 words, with its own page advising that 300 or more produces more reliable scores. |
| What independent testing found | None. It was not among the fourteen tools in Weber-Wulff et al. (2023), the seven in Perkins et al. (2024), the seven in Liang et al. (2023), or the four in the 2025 NBER working paper. Every public accuracy figure for it comes from its own testing of its own product. | None specific to it. It cites RAID, an independent benchmark, for a detection rate — but RAID measures how much AI text a tool catches, not how often it flags human writing. |
| What the vendor claims | 78% and 84% on its own thirty-text benchmark, in which its own brands took the top three places. | A 99% detection rate, citing RAID. That is a detection rate, not a false-positive rate; they publish the first and not the second. |
| What the vendor says about its limits | Its premium tier is described as adding GPT-4 detection, with the free detector handling GPT-2, GPT-3 and GPT-3.5 at “average accuracy”. | States that when the result is unclear the model tends to classify text as human-written, names heavily paraphrased writing and formulaic legal and academic prose as what it gets wrong, and says never to rely on an AI detector alone. |
| What happens to your text | Its detector page states “we do not store or share your data”. We found no statement there about training use in either direction, so treat that as unstated rather than denied. | Not established from its published pages by us. |
Every line above is summarised from our own examination of each tool, where the studies and vendor documents behind it are quoted and linked: Scribbr and QuillBot.
The ownership is the headline. Learneo, Inc. lists both Scribbr and QuillBot in its portfolio, alongside Course Hero, CliffsNotes, LitCharts, Symbolab, Bartleby and LanguageTool. Scribbr's detector comparison discloses no relationship between the two brands taking its top places.
Read as marketing research, that page is better than most of the category: the methodology is described openly, the test categories are listed, and its caveats are more honest than several competitors bother with. Read as a benchmark, it will mislead you. The sample was thirty texts of 1,000–1,500 characters, six categories of five, so each individual text moves the score by 3.3 percentage points. In it GPTZero scored 52% and Copyleaks 66% — which sits oddly beside peer-reviewed work in which Copyleaks was the best of seven tools and Turnitin the best of fourteen. Two of the six test categories used the tester's sister product as the attack.
On the tools themselves the practical difference is shape. Scribbr gives unlimited checks with no sign-up, capped at 1,200 words per submission — genuinely one of the least restricted free options anywhere. QuillBot publishes no scan cap but sets a floor instead: a minimum of 80 words, with its own page advising that 300 or more produces more reliable scores.
What each says about its own limits is where they genuinely diverge, and QuillBot comes out ahead. QuillBot states that when a result is unclear its model tends to classify text as human-written, which means a “human” verdict from it carries less information than an “AI” one — an unusually direct disclosure of a threshold choice. It also names heavily paraphrased writing and formulaic legal and academic prose as what it gets wrong, and says never to rely on an AI detector alone. Scribbr's equivalent disclosure is narrower: its free detector handles GPT-2, GPT-3 and GPT-3.5 at what it calls average accuracy, with GPT-4 detection reserved for premium.
The practical shapes differ in a way that matters more than either company's accuracy claim. Scribbr's 1,200-word cap means a standard undergraduate essay goes through in two pieces, and every detector in this category is least reliable on short passages — so the tool's own limit pushes you into its weakest operating condition. QuillBot's 80-word floor and 300-word recommendation point the other way, asking for more text rather than less.
Neither has been tested independently in a way that supports a ranking. Scribbr appears in none of the four studies this site tracks — not Weber-Wulff et al. (2023), not Perkins et al. (2024), not Liang et al. (2023), not the 2025 NBER working paper. Every public accuracy figure for Scribbr's detector, including the 78% and 84% quoted widely, comes from Scribbr's own testing of its own product.
QuillBot's position is slightly different but no stronger for a reader worried about being wrongly flagged. It cites RAID, which is a genuine independent benchmark, for a 99% detection rate. A detection rate measures how much AI text a tool catches. It says nothing about how often the tool flags human writing, and that is the number that matters if you are the one being accused. They publish the first and not the second.
So the honest position is that these two are the least independently evidenced detectors covered on this site, and the ranking most often used to choose between them was published by their shared owner.
It is worth stating what would change this assessment, because that is what makes it a judgement rather than a position. If either detector were entered into an independent multi-tool evaluation and performed well, this page would say so — the objection here is not to the tools but to the absence of any measurement of them that was not produced by their owner. Sixteen detectors have been tested by somebody independent; these two have not.
Both of these are free detectors attached to businesses that make money elsewhere, which is the fact that explains most of their behaviour. Scribbr sells academic editing, proofreading and citation services; QuillBot sells a paraphrasing and writing suite. Neither needs the detector to earn anything, and both need it to bring people to a site.
That shapes the incentive in a specific direction, and it is not the direction people assume. A detector sold to institutions has to defend its false-positive rate to a customer who will hear about every wrong flag. A free detector used as an acquisition surface has to be *run*, which rewards being permissive and pleasant rather than strict — and QuillBot has documented exactly that, stating its model resolves unclear cases towards human.
The common owner is the part that changes how you should read both companies' published research. Learneo, Inc. holds Scribbr and QuillBot alongside Course Hero, CliffsNotes, LitCharts, Symbolab, Bartleby and LanguageTool. When Scribbr publishes a ranking of AI detectors in which Scribbr and QuillBot take the top three positions, the relationship between the tester and two of the winners is not disclosed on that page.
Neither of these is likely to be the tool that flagged you in an academic process, and that is the most useful thing to say first. Institutions run Turnitin and Copyleaks. If a Scribbr or QuillBot result is being used against you, the first question is why a free consumer tool with no independent testing behind it is deciding anything.
That question is stronger than it may feel to ask. Scribbr appears in none of the four studies this site tracks — not Weber-Wulff et al. (2023), not Perkins et al. (2024), not Liang et al. (2023), not the 2025 NBER working paper. Every accuracy figure published for it was produced by Scribbr about Scribbr. An institution acting on it is acting on a vendor's self-assessment of an unbenchmarked classifier.
If you ran one of these on your own writing and it frightened you, read the result in the direction each tool documents. A QuillBot verdict of human carries less information than a verdict of AI, because the model is built to resolve doubt towards human. And QuillBot's own page names formulaic academic prose as a known weak point — meaning careful, conventional writing is the kind it most often gets wrong. That is a statement about the tool, not about your paper.
We cannot say which of these is more accurate, because there is no independent measurement of either. This is the only pair on this site where that is true of both sides, and it is why the page argues about incentives and disclosure rather than about performance.
QuillBot cites RAID, a genuine independent benchmark, for a 99% detection rate. We could not establish a false-positive rate for it from any source, vendor or independent — and that is the number that matters to anyone at risk of being wrongly flagged.
We could not establish whether either company uses submitted text for training. Scribbr's detector page states it does not store or share data, and says nothing either way about model training; QuillBot publishes nothing on the point that we could find. Treat both as unstated rather than as denials.
Neither company publishes a price for its detector, because neither sells one. What that costs you is not money.
Pick Scribbr if you want the most permissive free check available — unlimited runs, no account, 1,200 words at a time — and you are treating the output as a rough signal rather than as evidence.
Pick QuillBot if you want the tool that is most explicit about its own failure modes. Knowing that unclear results skew towards “human”, and that formulaic academic prose is a known weak point, tells you more about how to read a score than any accuracy percentage either company publishes.
A detector reports how statistically machine-typical a piece of prose reads. It has no access to how the text was produced, so it cannot establish authorship in either direction — a flag is not evidence of AI use, and a clean result is not a clearance. If you have been accused on the strength of one, drafting history is what actually answers it. And if your institution requires you to disclose AI assistance, disclose it — nothing on this page changes that obligation.