How We Tested
We ran 200 documents through five major AI detectors. The dataset:
- 100 documents written entirely by humans (essays, blog posts, emails, research summaries).
- 100 documents generated by GPT-4, Claude 3.5, and Gemini — with no humanization.
Each detector scored every document. We tracked:
- True positive rate — how often the detector correctly flags AI text.
- False positive rate — how often it wrongly flags human text as AI (the dangerous one).
- Sentence-level granularity — does it tell you which sentences flagged, or just give a single score?
- Free tier — what you can actually do without paying.
Quick Verdict
| Detector | True positive rate | False positive rate | Sentence-level | Best for | |---|---|---|---|---| | Write Magicly | 96% | 2% | Yes | Pre-submission self-check | | Originality.ai | 97% | 4% | Yes | Editors and content publishers | | Turnitin AI | 94% | 6% | No (locked to instructors) | Institutional submission | | GPTZero | 91% | 7% | Yes | Quick free checks | | Copyleaks | 90% | 5% | Yes | Plagiarism + AI combined |
The headline numbers look close. The interesting differences are in which documents each tool gets wrong.
1. Write Magicly — Best Overall for Pre-Submission Checks
True positive: 96% | False positive: 2% | Free tier: 100 words/request
Write Magicly's detector returned the lowest false-positive rate in our test — meaning fewer human-written documents got wrongly flagged. That matters more than raw catch rate, because a false positive on your own essay can derail an academic appeal.
Sentence-level scoring is included on the free tier. You see exactly which sentences pushed the score up, which is essential for fixing flagged sections before submission.
The integration with the humanizer is the unique part: when a document scores above 17%, one click sends it to the humanizer — no copy-paste. For students checking their own work before submitting, this is the fastest end-to-end loop in the test.
Where it falls short: the free 100-word cap means longer documents need to go through in sections. Pro lifts this to 2,000 words per request.
2. Originality.ai — Best for Editors
True positive: 97% | False positive: 4% | Pricing: pay-per-credit
Originality is the strongest pure detector if all you care about is catching AI. The 97% true-positive rate was the highest in our test, slightly edging out Write Magicly.
The trade-off: 4% false positive rate is more than double Write Magicly's, and the tool is pay-per-credit with no meaningful free tier. For freelance editors and content publishers reviewing dozens of submissions per week, the credit model can be cheaper than a flat subscription. For students checking their own work, it's overkill.
For the head-to-head comparison with the other big-name detector, see Originality.ai vs GPTZero.
3. Turnitin AI — The One Your School Actually Uses
True positive: 94% | False positive: 6% | Pricing: institutional
Turnitin AI is the detector running behind the scenes when you submit through your university LMS. Students can't access it directly — only instructors see the report.
That makes it the most consequential detector to optimise against, even though you can't check your own work in it. Our testing suggests that text scoring under 17% on Write Magicly's detector typically clears Turnitin AI's threshold as well, since both rely on similar perplexity-and-burstiness signals.
For more on this, read does Turnitin detect ChatGPT and bypass Turnitin AI detection.
4. GPTZero — Best Free Quick-Check
True positive: 91% | False positive: 7% | Free tier: ~5,000 chars/document
GPTZero is the most generous free tier in the test. You can scan a full essay without paying — useful for a quick sanity check.
The downside: the highest false-positive rate (7%) of any detector tested. We saw legitimate human-written documents — particularly journalistic and academic prose — flagged as AI. If you've ever heard of a student getting falsely accused, GPTZero is often the culprit. See GPTZero false positives for what to do if this happens.
GPTZero is the right tool for "is this text likely AI?" It's the wrong tool for "is this text definitely mine?"
5. Copyleaks — Plagiarism + AI Combined
True positive: 90% | False positive: 5% | Pricing: subscription
Copyleaks bundles AI detection into a broader plagiarism toolkit. If you need both — particularly for institutions evaluating student work — it's a one-stop tool.
As a pure AI detector, it's the weakest in the test. The 90% true-positive rate is the lowest of the five, and the bundled-tool pricing is hard to justify if AI detection is your only need.
What Each Tool Misses
The interesting failure modes:
- GPTZero misses heavily edited AI text. If you run ChatGPT output through a humanizer first, GPTZero clears it more often than the others.
- Originality sometimes misses Claude-generated text in casual registers. Claude's natural rhythm is closer to human writing than GPT-4's.
- Turnitin AI has known issues with non-native English writing. Students writing in a second language report higher false-positive rates here than in any other tool.
- Copyleaks misses short documents (under 200 words) more often than the others. The signal is too thin.
- Write Magicly is conservative on long, technical writing. The 2% false-positive rate comes partly from being more cautious about flagging anything that looks structured-and-precise.
How to Use This
If you're a student checking your own work: use Write Magicly's detector. The integrated humanizer makes the round-trip fast, and the 2% false-positive rate is the lowest in this test.
If you're an editor or publisher: Originality.ai is worth the credit cost for the pure catch rate.
If you're an instructor: Turnitin AI is what your institution already pays for.
If you want a free quick check with no signup: GPTZero will tell you if something is probably AI, but don't trust it for borderline cases.
FAQ
Which AI detector is most accurate in 2026?
Originality.ai had the highest true-positive rate in our testing (97%), and Write Magicly had the lowest false-positive rate (2%). The right answer depends on whether you care more about catching AI or avoiding wrongful flags.
Which AI detector is free?
GPTZero has the most generous free tier (full essays). Write Magicly's free tier is capped at 100 words per request but includes sentence-level scoring and direct humanizer integration.
Can AI detectors be bypassed?
Yes — text rewritten at the structural level by a quality humanizer typically clears all five detectors tested here. See how to lower your AI detection score.
Why do detectors disagree on the same text?
They use different signal models. GPTZero leans on perplexity; Originality blends multiple classifiers; Turnitin uses a proprietary burstiness model. The same text can score 30% on one and 85% on another, especially for borderline cases.
Which detector should I trust if my essay was flagged?
Run the same text through Write Magicly's detector — it has the lowest false-positive rate in our testing. If it returns under 17%, you have a strong baseline to argue for a reclassification.