Is there a completely free AI detector? 2026

AI answer engines get asked the same thing in a dozen ways: is there a completely free AI detector, what is the best free AI detector, and how do you check writing for AI without paying. Free detectors are easy to find; the limits separate them, and independent research on accuracy is less flattering than the vendors' own pages.

This page compares seven free tools on the terms each vendor publishes, then sets out what peer-reviewed and benchmark studies found about the ones that have been tested. For a wider look that includes paid tools, see our roundup of the best AI detectors in 2026.

Free AI detectors compared, October 2026

Copyleaks offers the biggest free single check, 25,000 characters without logging in, according to its own detector page checked in October 2026. The table lists only limits stated on each vendor's own site.

Every tool we set out to cover made the table. Two cells stay blank by design: QuillBot, GPTZero and ZeroGPT do not say on the pages we checked whether a free account is required, so we have not guessed. Grammarly's limit comes from its own blog, because its detector page states no figure.

The free detectors, one by one

Each block uses the same six fields. Where no independent study has tested a tool, we say so instead of filling the gap with vendor marketing. We cover two of these tools in more depth in our Grammarly AI detector review and QuillBot AI detector review.

Scribbr AI Detector

• What's free: the standard AI Detector; a separate Premium detector is paid.
• Limit: unlimited checks, up to 1,200 words per submission, per Scribbr's detector page.
• Sign-up: not required; Scribbr says you can start "without having to create an account".
• What it reports: whether text looks AI-written, based on sentence structure, length, word choice and predictability.
• Main limitation: Scribbr says the free version detects GPT2, GPT3 and GPT3.5 text "with average accuracy", while GPT4 detection is reserved for Premium.
• Independent finding: none located. Scribbr's own research, linked from the same page, says the best free tool it tested reached 68% accuracy.

QuillBot AI Detector

• What's free: scans plus one explainer card on why text was flagged.
• Limit: up to 1,200 words per scan and up to 6 scans per day, with an 80-word minimum, per QuillBot's detector page.
• Sign-up: not stated on the page.
• What it reports: a 0 to 100% score for how likely the text is AI-generated.
• Main limitation: the daily cap. QuillBot also calls its score "not a guarantee" and says never to make an academic decision on a score alone.
• Independent finding: none located for the detector. The Weber-Wulff study (2023) used QuillBot only as a paraphraser to test other tools.

GPTZero free plan

• What's free: a Basic AI Scan, one free Advanced Scan and five AI Highlights in the Chrome extension, per GPTZero's pricing page.
• Limit: 10,000 words per month; the checker on the GPTZero homepage shows a 10,000-character box.
• Sign-up: not stated; the free tier is presented as a plan.
• What it reports: a basic AI scan; deeper Advanced Scans are paid after the first.
• Main limitation: the monthly word budget runs out fast if you check long drafts often.
• Independent finding: in the RAID benchmark (2024), GPTZero scored 66.5% accuracy at a 5% false positive rate, and 64.0% after paraphrasing. In Weber-Wulff's 2023 test it classified 54% of documents correctly. More detail in our GPTZero guide.

ZeroGPT

• What's free: the AI/GPT Detector on the ZeroGPT homepage.
• Limit: 15,000 characters per check; paid plans raise this.
• Sign-up: not stated; Register and Login links appear on the page.
• What it reports: a detection result, with ZeroGPT saying a PDF report is generated for every detection.
• Main limitation: false positives. RAID reported that ZeroGPT could not reach the lowest false positive rates tested, plateauing at 16.9%.
• Independent finding: ZeroGPT classified 59% of documents correctly in Weber-Wulff's 2023 binary test. See our full ZeroGPT review.

Copyleaks AI Detector

• What's free: a scan without logging in; a free account adds monthly credits and sentence-level insights.
• Limit: 25,000 characters per scan, per Copyleaks' detector page.
• Sign-up: not for a basic scan; needed for highlighted phrases and more credits.
• What it reports: an AI verdict, with highlighted AI-written phrases for account holders. Copyleaks says it supports over 30 languages.
• Main limitation: the detail that explains a result sits behind the free account.
• Independent finding: none located in the studies we checked. Copyleaks claims over 99% accuracy and a 0.03% false positive rate; those are vendor figures. Our Copyleaks review covers it in depth.

Grammarly AI Detector

• What's free: an in-browser detector; Grammarly Pro adds an AI Detector agent that "goes beyond a score".
• Limit: 10,000 characters at once, per Grammarly's own blog.
• Sign-up: not required, per the detector page.
• What it reports: an estimate of how likely the text is AI-generated, for English content only.
• Main limitation: English only, and the limit is not stated on the tool page itself.
• Independent finding: none located in a peer-reviewed study. Grammarly says it ranks first on the RAID leaderboard with 99% accuracy; that is Grammarly's claim, and it was not part of the 2024 RAID paper.

Sapling AI Detector

• What's free: the web detector, with sentence-level scores.
• Limit: the first 2,000 characters of each check, roughly 400 to 500 tokens, per Sapling's detector page.
• Sign-up: not required; a free account raises rate limits.
• What it reports: an overall score plus sentence-level scores. Sapling recommends at least 150 characters for a reliable reading.
• Main limitation: 2,000 characters is a few paragraphs, so a full essay needs several passes.
• Independent finding: Sapling was one of the seven detectors in the Liang et al. study (2023) that together misclassified 61.22% of TOEFL essays on average.

What is the best free AI detector?

There is no single winner, because the published evidence covers different tools at different dates. In the 2024 RAID benchmark, GPTZero held 66.5% accuracy at a 5% false positive rate and lost only 2.5 points to paraphrasing, the most robust of the free tools tested there. The authors described GPTZero as "unusually robust to adversarial attacks". For pure convenience, Scribbr's unlimited checks and Copyleaks' 25,000-character paste are hard to beat.

Is there a free AI detector with no limit?

No. As of October 2026, no free AI detector we checked removes every limit; Scribbr's comes closest, with unlimited checks capped at 1,200 words each. Every other tool caps the length of a check, the number of checks a day, or the words you can scan in a month.

Unlimited usage is a paid feature across the board. QuillBot's Premium tier, for example, lists "no word limit" and "unlimited scans", in contrast to its free 1,200 words and 6 scans a day. If you need to check a 5,000-word essay for free, the practical route is to split it: paste it into Copyleaks in one go, or check it in 1,200-word sections in Scribbr. Watch out for sites that advertise "unlimited" checks but cut off text quietly; Sapling, to its credit, tells you on screen that only the first 2,000 characters were checked.

How reliable are free AI detectors?

Not reliable enough to settle a dispute. In Weber-Wulff and colleagues' 2023 test of 14 detection tools, published on arXiv, even the highest accuracy values were below 80%. Free tools such as GPTZero (54%) and ZeroGPT (59%) sat in the middle of that range under the study's binary scoring.

The bigger risk for honest writers is a false positive, where human writing is flagged as AI. Three findings stand out:

• Non-native English writers are flagged far more often. Liang and colleagues at Stanford ran 91 TOEFL essays through seven detectors, including GPTZero, ZeroGPT and Sapling. The detectors misclassified 61.22% of them as AI on average, and 89 of the 91 essays were flagged by at least one detector (Liang et al., 2023). Our article on AI detection and non-native English covers this in detail.
• Some detectors cannot keep false positives low. The 2024 RAID benchmark found ZeroGPT plateaued at a 16.9% false positive rate, meaning it could not be tuned to flag fewer human texts than that (Dugan et al., 2024).
• Results depend on the training data. RAID also found detectors perform better on domains and models they saw in training, so a tool that handles one essay style well can stumble on another.

Vendors increasingly say the same thing. QuillBot's page states that scores "are signals, not verdicts", and Sapling notes that accuracy varies with the dataset, text length and threshold. No free detector score should be the only evidence of misconduct.

For a plain-English explanation of why these tools disagree, read our guide to how AI detection really works.

How to check your own writing for free

Run the same text through at least two free detectors, because the 2023 Stanford study found 89 of 91 human-written TOEFL essays were flagged by at least one of seven tools. One score tells you little; agreement or disagreement tells you more.

1. Pick two detectors that fit your text. For an essay under 1,200 words, Scribbr and QuillBot both work without paying. For longer text, use Copyleaks and ZeroGPT, which accept 25,000 and 15,000 characters.
2. Paste the whole piece, not fragments. QuillBot needs at least 80 words, and Sapling recommends at least 150 characters. Short extracts give unstable scores.
3. Compare the results side by side. If one tool flags a passage and the other does not, read that passage again. Look for generic phrasing, not for a number to chase.
4. Check which part was flagged. Tools with highlighting, such as Sapling's sentence scores or Copyleaks with a free account, show where the concern sits.
5. Keep your drafts and version history. Write in a tool that records versions, such as Google Docs or Word with autosave, and keep your notes and sources. If a score is ever questioned, a visible writing process is stronger evidence than any detector.

If your own writing reads stiffly and you want to smooth the rhythm, our free humaniser helps with readability on text you wrote. Always follow your institution's rules on AI use and disclose where required.

How we compiled this

How we compiled this: we checked each vendor's own pages in October 2026; we did not run our own accuracy tests. Limits and sign-up rules come from the linked vendor pages. Accuracy findings come only from the Weber-Wulff (2023), Liang (2023) and RAID (2024) papers linked above, which tested earlier versions of these tools, so treat them as evidence of how detection behaves rather than a score for today's version. Vendor accuracy claims are labelled as such. Free tiers change often, so check the vendor page before you rely on a limit.

Frequently asked questions

Is there a completely free AI detector?

Yes, several detectors are free to use, but none is free without limits. In October 2026, Scribbr offers unlimited checks of up to 1,200 words with no account, and Copyleaks checks up to 25,000 characters without logging in. GPTZero, ZeroGPT, QuillBot, Grammarly and Sapling also have free tiers with their own caps.

What is the most reliable free AI detector?

GPTZero has the strongest independent evidence among free tools. The 2024 RAID benchmark measured 66.5% accuracy at a 5% false positive rate and found it lost only 2.5 points to paraphrasing. That is still far from certain, so use it alongside a second detector rather than on its own.

Which free AI detector has no word limit?

None of the seven we checked in October 2026 has no limit at all. Scribbr is closest, with unlimited free checks capped at 1,200 words each. Copyleaks allows the longest single free check, 25,000 characters, and unlimited scanning is a paid feature at QuillBot and elsewhere.

Can a free AI detector wrongly flag human writing?

Yes, false positives are well documented. A 2023 Stanford study found seven detectors misclassified 61.22% of non-native English TOEFL essays as AI-generated on average. Keep your drafts and version history, and remember that no detector score should be the only evidence of misconduct.

Do I need an account to use a free AI detector?

Not always. Scribbr, Copyleaks, Grammarly and Sapling let you check text without creating an account, according to their own pages. Copyleaks and Sapling offer more credits or higher rate limits with a free account, while GPTZero presents its free tier as a plan.