The short version
There is no best AI detector, because the tools are built for different buyers. Turnitin is built for institutions and lives inside the LMS. Copyleaks is built for enterprise compliance pipelines. GPTZero is built for educators who want dashboards. Winston is built for content agencies with documents to upload. Sapling is built into a customer-experience platform. And ai-detector.co, this site, is built for a person with a text and a question, who wants an honest answer in ten seconds without creating an account.
The field, one table
| Criteria | The field | ai-detector.co |
|---|---|---|
| Turnitin | Institutional only, LMS-integrated, sentence-level AI report for instructors | Free, public, paste-and-scan |
| GPTZero | Education dashboards, document uploads, free tier with caps | No caps tied to accounts, no dashboards |
| ZeroGPT | Free with heavy ads, decimal-point percentages | No ads, explicit inconclusive band |
| Copyleaks | Enterprise API, plagiarism + AI in one pipeline | AI reading only, no procurement needed |
| Winston AI | Paid, document uploads and OCR, 99%+ accuracy marketing | Free, text-only, no accuracy theater |
| Sapling | Sentence-level highlighting inside a CX platform | Whole-text reading, standalone |
What our samples showed
On clearly machine-written text (unedited GPT, Claude and Gemini longform), every tool in the list lands in its AI band most of the time. On clearly human text, most tools read human most of the time, with ZeroGPT the most trigger-happy in our runs. The separation collapses on the middle category: AI drafts with substantial human revision split the field on nearly every sample. That is not a flaw of any single tool. It is the honest state of the science, and any vendor whose marketing implies otherwise is describing their curated test set, not your text.
Vendor accuracy claims (98%, 99.8%) come from internal test sets that exclude the hard cases: edited AI text, non-native writing, formulaic genres. Independent academic tests consistently measure lower, with significant false positive rates on real student writing. Treat every published accuracy number, including any future number of ours, as an upper bound under laboratory conditions.
Tool-by-tool notes
Turnitin
The institutional default, sold only to schools and integrated into LMS submission flows. In-house engine, sentence-level report, scores suppressed at the low end after its own false positive disclosures. If you are a student, this is most likely the engine reading your work; our accuracy deep dive covers what its percentage does and does not mean.
GPTZero
The education specialist: class dashboards, batch uploads, and a Doc-replay feature that examines writing process rather than texture. Published methodology, reasonable middle-of-field strictness. Free tier is capped tightly enough to push regular users toward paid plans.
ZeroGPT
The traffic king. Free, fast, ad-supported, decimal-point percentages that look more precise than the science permits, and the most aggressive flagging of formal human prose in our runs. Fine for curiosity, risky as evidence.
Copyleaks
The enterprise pipeline: AI plus plagiarism in one API, LMS and SSO integrations, broad language coverage. Built for procurement, not for a person with one draft. Strong choice when compliance paperwork is part of the requirement.
Winston AI
The document processor: uploads, OCR for scans and images, client projects, exportable reports. The 99.98% accuracy banner should be read as marketing, but the workflow is real and agencies get value from it.
Sapling
The editor's option: per-sentence probability highlighting inside a CX writing suite, plus a clean developer API. Sentence scores are noisy by nature, but as a revision aid they are genuinely useful.
ai-detector.co, this site
The honest free reading: no account, nothing stored, an explicit inconclusive band, and copy that says what a score cannot prove. No uploads, no dashboards, no API yet. We built it for the person with a text and a question, and the rest of this guide tells you when you have outgrown it.
Where the field is heading
Three currents will reshape this comparison within a year or two. Watermarking is the wildcard: if major model providers ship verifiable text watermarks with shared standards, detection shifts from statistical guessing to cryptographic checking, and every tool on this list rebuilds or dies. Provenance standards like C2PA are arriving for images first, but the framework of signed content history points the same direction for text. And model convergence keeps eroding the statistical signal as assistants write ever more like people, which widens honest tools' inconclusive bands and inflates dishonest tools' confidence theater. Our advice survives all three futures: prefer tools that state their uncertainty, distrust precision that outruns the science, and never let any single number, from any vendor in any era, stand alone against a person.
How to choose
You are an individual with occasional checks. Use a free no-account tool. We are obviously one of them; the ZeroGPT comparison covers the other big free option honestly.
You are a teacher without an institutional license. A free tool plus a process-evidence policy beats a paid tool used as a verdict machine. The workflow is on the teachers page.
You run institutional enforcement. You will end up with Turnitin or Copyleaks for integration reasons. Read the Turnitin accuracy data before you write the policy, and write the inconclusive band into it.
You process documents at volume. Winston’s uploads and OCR or Copyleaks’ API are the practical options today; our API is planned but not live, and we say so rather than waitlisting you.
You need sentence-level analysis. Sapling’s highlighting is genuinely useful for editing workflows; the Sapling comparison maps where each fits.