The best AI detectors with no word limit in 2026
AI detectors with no word limit are rare in 2026. Most cap each check, often at 1,200 words or 15,000 to 25,000 characters on free plans, and many "unlimited" plans mean unlimited checks rather than unlimited length. Below is a sourced table of the free and paid limits for 15 tools, the best picks if you need to check long text without cutting it up, and what it takes to check a whole thesis or manuscript.
Quick picks. Best free with no limits: IsThisAiWritten. Best paid plan with no word limit for detection: QuillBot Premium. Best overall accuracy: Pangram, if you can split text into 18,725-word pieces. Best for schools: Copyleaks, whose web platform has no character maximum and which connects to most LMS platforms.
AI detectors with no word limit, and the limits of the rest
Limits per single check, as published on each tool's own pages at the time of writing (October 2026). Characters include spaces; 10,000 characters is roughly 1,500 to 1,700 words of English.
| Tool | Free limit per check | Free volume cap | Account for free use | Largest paid check |
|---|---|---|---|---|
| IsThisAiWritten | None | None | No | n/a (free) |
| Pangram | About 2,000 words (the daily allowance) | 20 credits a day | Yes | 18,725 words |
| GPTZero | 10,000 characters | 10,000 words a month with an account | No, for one scan | 150,000 characters |
| Copyleaks | 25,000 characters | Limited free credits with an account | No | 2,000 pages, no character maximum |
| ZeroGPT | 15,000 characters | Not stated | Not stated | 350,000 characters; unlimited on Enterprise |
| Originality.ai | 2,000 words | 3 scans a day | No | Not stated |
| Winston AI | Trial only | 2,000 credits over 14 days | Yes | 200,000 characters |
| QuillBot | 1,200 words | 6 scans a day | Not stated | No word limit (Premium) |
| Scribbr | 1,200 words | Unlimited checks | No | 25,000 words (premium check) |
| Grammarly | 25,000-character box | Not stated | Not stated | Not stated |
| Sapling | First 2,000 characters | Not stated | Not stated | 100,000 characters (Pro) |
| Decopy | 200,000 characters | 5 uses (10 with an account) | No | 200,000 characters |
| Undetectable.ai | 10,000 words | Not stated | No | Plans list "Unlimited AI Detecting" |
| Quetext | 1,000 words | Not stated | No | Not stated (100,000 words a month on Essential) |
| Turnitin | Institutions only | n/a | Via institution | 30,000 words, 100 MB |
Sources for every row are listed at the end. "Not stated" means we could not find the figure on the tool's own pages.
Why most AI detectors cap length
Detection models read text in chunks, and scoring every chunk of a long document costs compute. For a company running the model on its own servers, length is a direct cost, so limits are how free plans are kept affordable and paid plans are priced (by words, credits or characters). A detector that runs on your own device does not have that cost, which is why a free tool can afford to have no limit.
Splitting a long text to fit a cap works, but it has side effects. Each piece is judged without the rest, short pieces give noisier results, and you have to stitch the scores back together yourself.
1. IsThisAiWritten
Best for: checking long text for free, in one go, without uploading it.
Our own tool, and the reason this article exists. There is no word or character limit and no account; a 208,000-word novel was analysed in a single pass. The detector model downloads once and runs in your browser, so the length of your text costs us nothing and it never leaves your device. Every word is scored, however long the text; our methodology page explains how.
- Pro: truly no limit, free, and private.
- Pro: a sentence map and, for fiction, a descriptive narrative fingerprint.
- Con: English only.
- Con: a long document takes longer to score on a slower device.
Price and limits: free; minimum 50 words.
2. QuillBot Premium
Best for: a paid plan with no word limit for detection and many languages.
QuillBot's detector page lists "No word limit for detection scans" and "Unlimited scans" for Premium, and it supports more than 20 languages. Free users get 1,200 words per scan and six scans a day. QuillBot cites a 99% detection rate from its RAID benchmark entry, submitted in January 2025; RAID uses older AI models.
- Pro: no length limit and unlimited scans on Premium.
- Pro: labels AI-refined text separately from fully AI-written text.
- Con: no recent independent study we could find.
- Con: uses inputs for training by default; the opt-out is in its browser extension.
Price and limits: Premium pricing varies by region; free tier 1,200 words per scan.
3. Copyleaks
Best for: long documents in schools and companies, in many languages.
Copyleaks' FAQ lists the web platform's maximum as 2,000 pages, with no character maximum, and free scans of up to 25,000 characters without logging in. It can combine AI and plagiarism checks in one report. Paid volume is set by credits, where one credit covers up to 250 words. Copyleaks has decent independent evidence: very few false positives in a 2026 peer-reviewed study, though it underestimated AI content there.
- Pro: very long documents on the web platform, and over 30 languages.
- Pro: LMS integrations including Canvas, Moodle, Blackboard and D2L.
- Con: a 300,000-word monthly allowance on Personal is used up by a few books.
- Con: scans are used for training unless you opt out.
Price and limits: Personal is $16.99 a month ($13.99 billed yearly) for 1,200 credits, about 300,000 words.
4. Winston AI
Best for: large single scans on a paid plan.
Winston AI allows up to 200,000 characters per scan on paid plans, roughly 30,000 words, with no limit on scans per hour. It reads uploaded .docx, .pdf and image files with OCR, which helps with scanned pages. Credits are counted per word, so your monthly allowance is the real ceiling. Its September 2026 RAID entry is the top result on that leaderboard.
- Pro: one of the largest per-scan limits among paid tools.
- Pro: does not train on submitted text without opt-in consent.
- Con: needs an account; free use is a 14-day trial of 2,000 credits.
- Con: 100,000 words a month on the entry plan.
Price and limits: Essential lists at $18 a month or $10 billed yearly for 100,000 credits.
5. GPTZero Professional
Best for: long checks from a tool with strong independent results.
GPTZero's Professional plan takes up to 150,000 characters per scan and 500,000 words a month, with overage available. Premium is limited to 50,000 characters per scan. In independent tests GPTZero kept false positives low but missed more humanized text than Pangram.
- Pro: well-tested detector with a high per-scan ceiling.
- Pro: batch upload of up to 250 files on Professional.
- Con: free scans stop at 10,000 characters.
- Con: keeps a copy of text submitted through its dashboard.
Price and limits: Professional is $45.99 a month or $24.99 billed yearly.
6. Decopy
Best for: an occasional long free check without an account.
Decopy's detector takes up to 200,000 characters with no sign-up, by far the largest free box among the server-based tools we checked. The catch is volume: visitors get five uses, or ten after registering. Decopy publishes no accuracy figures and says that "no AI detection tool can be 100% accurate". Its FAQ says it does not permanently save your content.
- Pro: very large free check, no account.
- Pro: reports AI, mixed and human percentages with sentence highlights.
- Con: no published accuracy data or independent tests.
- Con: only a handful of free uses.
Price and limits: paid plans from $9.99 a month.
7. Pangram
Best for: accuracy first, with long texts split into pieces.
Pangram is in this list for one reason: it has the best independent accuracy record of any detector, including a peer-reviewed 2026 study of academic papers. Its dashboard caps each scan at 18,725 words and files at 30 MB, so a thesis or book needs splitting, and the free plan covers only about 2,000 words a day. Since Pangram 4, API use is billed at $0.05 per 100 words, which Pangram says can cost up to 10 times more than before for long documents.
- Pro: strongest independent evidence, including on humanized text.
- Pro: labels AI-assisted passages separately, useful in long mixed documents.
- Con: per-scan cap and small free allowance.
- Con: an account is required.
Price and limits: Individual is $20 a month or $15 billed yearly for 300,000 words.
AI detectors for long documents: theses, manuscripts and books
A long document raises two questions a short one doesn't: how many pieces you have to cut it into, and what one check costs. Our worked example is a 90,000-word manuscript or long thesis, about 540,000 characters if you allow 6 characters per word including spaces. Scan counts are our estimates from each tool's stated per-scan limit; prices are in US dollars at the time of writing.
| Tool | Checks needed | What this one check uses or costs |
|---|---|---|
| IsThisAiWritten | 1 | Free |
| Copyleaks | 1 (up to 2,000 pages) | 360 of the 1,200 monthly credits on the $16.99 Personal plan |
| Winston AI | About 3 | 90,000 of the 100,000 monthly credits on the $18 Essential plan |
| Sapling API | 3 | About $2.70 |
| GPTZero Professional | About 4 | 90,000 of 500,000 monthly words, or about $41 as overage |
| Pangram | 5 | 90,000 of 300,000 monthly words on the $20 plan, or about $45 via the API |
| Originality.ai | Not stated | 900 of 2,000 monthly credits on the $14.95 Pro plan, 1,800 with plagiarism checking |
The API figures use Pangram's $0.05 per 100 words, GPTZero's published overage rate of $0.00046 per word and Sapling's $0.005 per 1,000 characters. Sapling's API takes up to 200,000 characters per request and offers a no-data-retention option, but you need to write code to use it, and Sapling publishes no headline accuracy figure.
Long documents are often mixed: a human-written thesis with an AI-polished literature review, or a novel with a few generated chapters. One score for the whole file can hide that, so a tool that scores segments or sentences tells you more than a headline percentage. Pangram labels each segment human, AI-assisted or AI; GPTZero and Sapling score sentences; our report has a sentence map and, above 30,000 words, shows the text in pages of 5,000 words with a chapter jump menu. If you have to split, cut at chapter breaks, keep the pieces long and read the pattern across the whole document rather than one piece's score.
To check a thesis or manuscript here, open it as a .txt or .docx file, which is read in your browser and not uploaded, or copy the text out of a PDF. About 30,000 words take two to three minutes on a typical laptop and a full novel 15 minutes or more, with partial results along the way and a cancel button. Like any detector, it can be wrong in both directions, so treat a result as a reason to look closer, not as proof. For fiction the report adds a descriptive narrative fingerprint based on the StoryScope research (Russell et al., COLM 2026), which is not used in the verdict.
How we compared
Between 16 and 18 October 2026 we opened each tool's detector page, pricing page and help articles and copied the stated limits into the table, noting units (words or characters) exactly as published. Where a page gave no figure we wrote "Not stated" rather than estimating. For the long-document example we worked out scan counts and costs for a 90,000-word manuscript from those limits and prices; that arithmetic depends on our 6-characters-per-word assumption. IsThisAiWritten is listed first because it is our own tool and the free, private option with no limit. The other picks favour tools that let you check long text in one piece, with accuracy notes drawn from independent research or labelled as vendor claims. We did not upload a full manuscript to each tool.
Sources
- Pangram, Minimum and maximum input sizes, checked October 2026
- Pangram, What do I get with a free account?, checked October 2026
- Pangram, Subscription tiers, checked October 2026
- Pangram, Introducing Pangram 4, checked October 2026
- GPTZero homepage, checked October 2026
- GPTZero pricing, checked October 2026
- GPTZero, Word limit overages, checked October 2026
- Copyleaks AI Detector and FAQ, checked October 2026
- Copyleaks pricing, checked October 2026
- ZeroGPT pricing, checked October 2026
- Originality.ai pricing, checked October 2026
- Winston AI pricing, checked October 2026
- Winston AI, How to use Winston AI for text analysis, checked October 2026
- QuillBot AI Detector, checked October 2026
- Scribbr AI Detector, checked October 2026
- Scribbr, How does the AI Detector work?, checked October 2026
- Grammarly AI Detector, checked October 2026
- Sapling AI Content Detector, checked October 2026
- Sapling pricing, checked October 2026
- Sapling, AI detector API, checked October 2026
- Sapling, Data handling, checked October 2026
- Decopy AI Detector, checked October 2026
- Decopy pricing, checked October 2026
- Undetectable.ai AI Detector, checked October 2026
- Undetectable.ai pricing, checked October 2026
- Quetext AI Detector, checked October 2026
- Quetext pricing, checked October 2026
- Turnitin, AI writing detection capabilities FAQs, checked October 2026
- iThenticate pricing, checked October 2026
- RAID Benchmark leaderboard, checked October 2026
- Jabarian and Imas, Artificial Writing and Automated Detection, checked October 2026
- Van Vlasselaer, Van Droogenbroeck and Spruyt (2026), checked October 2026
- Russell et al., StoryScope, checked October 2026
- IsThisAiWritten methodology: long documents
Questions
Which AI detector is the most accurate for long text?
On independent evidence, Pangram. In a University of Chicago working paper by Jabarian and Imas, all three commercial detectors tested were most reliable on medium and long passages, and Pangram had a zero false positive rate on long ones; GPTZero and Originality.ai also did well there. Pangram caps each scan at 18,725 words, so a book or thesis has to be split.
What does 'unlimited' mean on AI detector pricing pages?
Usually unlimited scans, not unlimited length. Scribbr's free tool allows unlimited checks of up to 1,200 words each, for example. QuillBot Premium is one of the few paid plans that advertises no word limit for detection itself.
Does iThenticate check manuscripts for AI writing?
Not on its individual plans. iThenticate, Turnitin's manuscript checker, lists AI writing detection as not available on its single-manuscript and three-manuscript options at the time of writing. One manuscript of up to 25,000 words costs $125, for example.
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