Undetectable AI detector review
Verdict
A free, high-capacity checker whose accuracy case rests on one cited study and a table of media reviews the vendor compiled, from the company that sells the humanizer it is meant to check
- Best for
- A quick, no-account check on a long English text, read as one opinion beside a detector the vendor does not own
- Main limitation
- The accuracy figures are either the vendor's own or lifted from third parties into a table the vendor built, with no test of its own published, and the page does not say which outside checkers its probability imitates, read 9 November 2026
Plans and limits
| Plan | Price | Humanizer words a month | Detector | Checked on |
|---|---|---|---|---|
| Free detector | $0, no account | n/a | Up to 10,000 words per check | 9 November 2026 |
| Humanizer free trial | $0 | 250 words in total | Unlimited AI detecting listed | 9 November 2026 |
| Entry plan, yearly | $5.00 a month, charged $60.00 a year | 10,000 | Unlimited AI detecting listed | 9 November 2026 |
| Entry plan, monthly | $9.99 a month | 10,000 | Unlimited AI detecting listed | 9 November 2026 |
| Next plan, yearly | $9.50 a month, charged $114.00 a year | 20,000 | Unlimited AI detecting listed | 9 November 2026 |
The 10,000-word box is the largest single input among the detectors from humanizer vendors on this site: Phrasly states no maximum but sets a 30-word minimum, Stealthly's free plan allows 300 detector words a month, and Walter Writes AI's detector page states no cap, all read 9 November 2026. The yearly toggle was selected by default on the pricing page, and the monthly rate was visible only after switching it.
The detector itself is free and account-free, and the pricing page lists "unlimited AI detecting" as a feature of every paid plan, read 9 November 2026. The paid plans are priced on humanizer words, so a reader pays for the rewrite and gets the detector beside it.
What it did to our text
Does the Undetectable AI detector work?
Undetectable AI's detector is free, needs no sign-up, accepts up to 10,000 words per check and claims more than 99 percent accuracy, read on its detector page on 9 November 2026. This Undetectable AI detector review covers what the vendor says the checker does, what evidence it offers, and why a humanizer company's own detector cannot be the judge of that company's humanizer. The rewrite tool is reviewed in the Undetectable AI review, and the combined tools sit in the humanizer and detector list.
What does the vendor publish about its method and rates?
Less about method than about reputation. The detector page states that the tool uses linguistic, semantic and pattern-analysis models trained to identify AI writing, that it shows the AI detection probability from major checkers, and that it flags paraphrased and rewritten AI text, read 9 November 2026. It names ChatGPT, Claude, Gemini, DeepSeek and others as covered models. It does not name the outside checkers whose probability it claims to show, or say whether those readings come from their APIs or from an imitation.
The accuracy case has two parts. First, a comparison table the vendor built from five media reviews, placing itself at 100 percent detection and 0 percent false positives against named rivals, read 9 November 2026. Second, a peer-reviewed study by Kar and colleagues in the Indian Journal of Psychological Medicine, which the vendor quotes as finding that Undetectable AI and one other tool detected all three software-generated texts in that study, read 9 November 2026. Three texts is the sample size the vendor's own quotation gives. A rival detector's self-reported rate, for comparison, is GPTZero's stated false positive rate of no more than 1 percent on its own benchmark (GPTZero, How GPTZero works, read 9 November 2026).
What does the research say about detectors in general?
Weber-Wulff and colleagues tested 14 AI text detectors on human, machine, paraphrased and translated text and found every one below 80 percent on their accuracy measure, with the tools disagreeing with each other on the same texts (Weber-Wulff et al. 2023, International Journal for Educational Integrity, read 9 November 2026). Sadasivan and colleagues showed that a paraphrasing step lowered the accuracy of every detector they tested, watermark-based ones included (Sadasivan et al. 2023, arXiv, read 9 November 2026).
Undetectable AI's detector page says the checker catches paraphrased AI text. Its humanizer page, read the same day, says the humanizer rewrites AI text so that it scores as human on detectors. Both claims come from one company, and one of them has to give way on any given text. No detector score should be the only evidence in a misconduct case.
Why is this detector not evidence about this humanizer?
The humanizer page shows the pairing plainly: a sample passage marked 99 percent AI by "other detectors", and the humanized version marked 99 percent human by "our detector", read 9 November 2026. A company that controls both the rewrite and the verdict can tune one against the other without any outside check. That is why the published method on this site scores every output on five detectors no humanizer vendor owns, GPTZero, Originality.ai, Copyleaks, Pangram and ZeroGPT, and never on a vendor's built-in checker.
| What Undetectable AI's detector page states (read 9 November 2026) | What it does not state |
|---|---|
| More than 99 percent accuracy proven by independent tests | A test of its own with a dataset, date and threshold |
| A peer-reviewed study found 100 percent detection and 0 percent false positives | That the quoted result rests on three software-generated texts |
| Shows the detection probability from major checkers | Which checkers, or how their readings are obtained |
| Detects paraphrased and rewritten AI content | How it reads the output of its own humanizer |
| Trusted by 24 million users | How the count is defined |
What does the Undetectable AI detector report?
A probability, a three-band colour key and, by the vendor's description, a comparison with other checkers. The humanizer page's sample shows a key of human, likely AI and AI, with a reading from the vendor's own detector and a second reading labelled "other detectors", split into free, standard and advanced bands, read 9 November 2026. Which detectors sit in each band is not stated. The detector page adds that the tool flags the parts of a text likely to be caught.
| Output described by the vendor | Useful for | Missing |
|---|---|---|
| Overall AI probability with a three-band key | A quick read on a long draft | The threshold between the bands |
| A second reading labelled "other detectors" | A sense of how a stricter checker might read it | The names of those checkers and how their readings are produced |
| Flagged passages | Finding what moved the number | Any stated minimum text length for a stable flag |
Who should use the Undetectable AI detector?
Use it as a free first pass on a long draft, with the understanding that its accuracy case is a vendor-built table plus a quoted study of three texts, and that the readings labelled as other detectors are unexplained. Anyone deciding a grade or a job on a score should read do AI detectors work and run the text through a detector the humanizer vendor does not own.
Do not use it to judge Undetectable AI's humanizer. The rewrite tool is reviewed on the same fields as every other tool in the Undetectable AI review, and the eight vendors that ship both a humanizer and a checker are compared in the humanizer and detector list. Every review on this site uses the same fields; see the reviews hub.
Questions about Undetectable AI detector
Is the Undetectable AI detector free?
Yes: the detector page states that the checker is free, needs no sign-up and accepts up to 10,000 words per check, read 9 November 2026; paid plans from $5.00 a month billed $60.00 yearly list unlimited AI detecting as a feature.
How accurate is the Undetectable AI detector?
The vendor claims more than 99 percent accuracy and cites a peer-reviewed study of free detectors by Kar and colleagues that, in the vendor's words, found 100 percent detection with no false positives, read 9 November 2026; the vendor publishes no test of its own with a dataset and date.
What does the Undetectable AI detector measure?
The page describes linguistic, semantic and pattern-analysis models and says the tool shows the detection probability from major checkers, read 9 November 2026, without naming which checkers it imitates or how.
Does the Undetectable AI detector prove the Undetectable AI humanizer works?
No: the same company sells the rewrite and the verdict, and its humanizer page shows the two tools side by side, so a human label from this checker on this humanizer's output is the vendor grading its own work.
Which languages does the Undetectable AI detector support?
English first and more than 50 others, with English stated as the most accurate, per the detector page's FAQ read 9 November 2026.
Related reading
Undetectable AI humanizer: what the feature does, its modes and limitsThe Undetectable humanizer feature reviewed: readability and purpose settings, the free basic model against.
Undetectable AI review: is it legit and does it work?Is Undetectable AI legit? Its plans, word limits and price checked on a stated date, what it changes in your.
Best AI detector and humanizer in one toolBest AI detector and humanizer in one tool: nine vendors that ship both, on the same dated fields, and why a.
How we test AI humanizersThe full humanizer test: 24 AI inputs and 6 human controls, five named detectors, a meaning rubric, published.