The 9 Best AI Detectors in 2026

Originality.ai is a paid detector built for people who publish content, not grade it: agencies, affiliate publishers and editorial teams checking freelance work before it goes live. Scans cost 1 credit per 100 words (2 credits with plagiarism included), and the Pro plan's 2,000 monthly credits at $14.95/mo cover 200,000 words, about 7 cents per 1,000. The company claims 99% accuracy on the latest models and 97.8% across 30 languages; treat both as vendor numbers.

The independent evidence is still the strongest on this list. In Scribbr's 12-tool comparison, Originality.ai scored 76%, just behind Scribbr's own premium checker, and it was the only tool that detected paraphrasing-tool use on human-written text in more than half of cases (60%), the exact trick most detectors miss entirely. Its free Chrome extension also records the writing process in Google Docs, so a wrongly flagged writer can replay how a draft was actually typed, a form of evidence no one else here offers.

The trade-off is aggression. The same test logged one false positive, and the tool errs toward calling borderline text AI, which is tolerable for content QA and unacceptable for accusing a student. Unlike GPTZero or ZeroGPT there is no everyday free tier, and there is no unlimited plan: heavy users buy credits, period.

QuillBot's AI Detector is the free checker to use first. It takes up to 1,200 words per scan, six scans a day, and instead of one blunt percentage it splits text into AI-generated, AI-refined and human-written portions, which matters now that most real documents are a mix. QuillBot publishes that the detector is independently evaluated on the RAID benchmark and states plainly that no detector can reach 100% accuracy, a level of honesty rare in this niche.

On measured results it earns the spot: 78% accuracy with zero false positives in Scribbr's comparison, tied for the best free score. The caveat worth knowing is corporate: QuillBot and Scribbr are both Learneo companies and their detectors are siblings, so the two "best free tools" in that test share DNA with the tester. Even so, no rival test has knocked either off the top of the free tier.

Premium at $8.33/mo (billed annually) removes the word cap, allows unlimited scans and adds full-text explainers. The weakness matches the category's: like every free tool tested, it caught only about 50% of AI text that had been mixed with human writing or run through a paraphraser, so a clean QuillBot result on "humanized" text means little.

GPTZero is the detector built around classrooms. Its pricing page counts "over 10 million teachers and students" and an official partnership with the American Federation of Teachers, and the product reflects it: sentence-level AI highlighting, mixed human-AI detection, batch upload of up to 250 files on the Professional plan ($24.99/mo billed annually), and LMS integration with Canvas and Google Classroom. The free tier is genuinely useful at 10,000 words a month, and Premium at $12.99/mo (billed annually) covers 300,000 words, about 4 cents per 1,000, the cheapest paid rate on this list.

Accuracy is the complicated part. Scribbr's comparison scored GPTZero just 52%, mostly because its verdicts behaved binarily, calling documents nearly all-AI or all-human. GPTZero has shipped multiple model generations since that test, but the pattern in user feedback persists: its Trustpilot page sits at 2.3 across 135 reviews, dominated by writers whose formal or polished human prose was flagged, while business users on G2 rate it 4.3.

Unlike Turnitin, anyone can use it today for free, and unlike Originality.ai it is priced and framed for education rather than content QA. Teachers should still use its scores the way GPTZero itself advises: as a conversation starter backed by the sentence highlights, not a verdict.

Copyleaks is the most platform-like tool here: AI text detection in 30+ languages, plagiarism checking in 100+, and since 2025 AI image detection, all drawing from one credit pool. The annual Personal plan is $13.99/mo ($167.88 billed yearly) for 1,200 credits, enough for 300,000 words or 1,200 images across the year; month-to-month it is $16.99 for 100 credits (25,000 words). That works out to roughly 56 cents per 1,000 words, about thirteen times GPTZero's Premium rate, which is why Copyleaks makes sense mainly when an institution, not an individual, is paying.

For organizations the depth is real: a browser extension, a Google Docs add-on, sitemap-wide website scanning and cross-language plagiarism detection on the Pro plan ($74.99/mo billed annually, 25 seats), plus LMS and API integrations that put it in Semrush's and Edmentum's stacks. No other tool on this list combines AI text, AI images and plagiarism in one report.

The honest counterweight: Scribbr's research measured 66% accuracy against the 99% Copyleaks advertises, and its Trustpilot score is 2.3 across 334 reviews, a mix of auto-renewal billing complaints and students reporting their own writing flagged as 100% AI. Budget for the subscription management, and never treat its score as a standalone verdict.

Winston AI is the only detector on this list that handles work that never existed as clean digital text. Its OCR pipeline accepts PDFs, scanned pages and photos of handwriting, extracts the text and runs detection on it, a workflow teachers with paper submissions and publishers digitizing archives cannot get from any paste-box competitor. Credits are literal: 1 word costs 1 credit for AI detection and 2 for plagiarism, so Essential's 80,000 monthly credits at $18/mo ($10/mo billed annually) mean 80,000 words of AI checking.

Winston advertises 99.98% accuracy across ChatGPT, Gemini, Claude and Llama output. No independent test has come close to confirming a number like that for any detector, and Winston was absent from Scribbr's 12-tool comparison, so buyers are trusting internal benchmarks. The company leans into credibility in another way: its HUMN-1 certification (Advanced plan, $29/mo) issues a verifiable human-content badge for websites, useful for agencies proving clean copy to clients.

Against the others, Winston costs more per word (about 23 cents per 1,000 on Essential monthly, versus 7 for Originality.ai) and has the thinnest public track record: 4.1 on Trustpilot from just 35 reviews. The free tier is really a 14-day, 2,000-credit trial, not an ongoing allowance like GPTZero's.

Scribbr's AI Detector is the least demanding tool on this list: unlimited free checks of up to 1,200 words each, no account, and a stated policy that submissions are not stored or shared, which matters if you are checking an unpublished thesis chapter. Its verdict distinguishes human-written, AI-generated and AI-refined text with paragraph-level feedback, so a student who ran a draft through a rewriting tool can see exactly which sections will look suspicious to a grader. It reads English, German, French and Spanish.

Scribbr also runs the most-cited public comparison of these tools, which is both a credential and a conflict: its own free detector scored 78% (tied with QuillBot, its Learneo sibling) and its premium checker took first place at 84% with zero false positives. Those numbers appear throughout this page because no vendor-independent test of comparable breadth exists, but grade the self-ranking accordingly.

The company's Trustpilot score of 4.3 across 15,648 reviews covers its proofreading business broadly, not the detector alone. Limits are the obvious ones: 1,200 words per submission means checking a dissertation in slices, and for anything longer or more advanced Scribbr itself points users to QuillBot's detector rather than selling a bigger plan.

Turnitin is the AI detector most students will actually be judged by, and the one none of them can buy. Its AI writing detection ships inside the institutional Originality and Feedback Studio products, integrated directly into the LMS, and licensing is strictly contact-sales, institution-wide. That distribution is why every other tool on this list exists: individuals check their work on GPTZero or Scribbr precisely because they cannot see what Turnitin will say.

Where consumer tools compete on catching everything, Turnitin publicly optimizes the other direction. Its stated position is a false positive rate under 1% at the document level, with the company writing that "if we say there's AI writing, we're very sure there is," while acknowledging a residual risk of false positives. That precision-first posture is the right call when a flag can trigger a misconduct hearing, and it is the opposite of Originality.ai's flag-first tuning for content QA.

The costs of that model are transparency and access. Because no individual can test it, claims cannot be independently audited the way Scribbr's research audits public tools, and G2 reviewers score the surrounding Feedback Studio at 4.3 from 125 reviews. Educators get a percentage and highlights as "insight," and Turnitin itself stresses the number is not proof of misconduct.

Sapling's AI Detector comes from an NLP company whose main business is a writing assistant for customer-support teams, and the detector inherits that engineering: a public, documented API you can wire into a CMS, a moderation queue or a hiring pipeline without booking an enterprise demo, which is exactly the friction Copyleaks and Turnitin impose. The free checker takes 2,000 characters (roughly 300-450 words); Pro at $25/mo ($12/mo billed annually) raises the paste limit to 100,000 characters, the largest single-check capacity on this list.

Sapling states a 97%+ detection rate and under 3% false positives on longer texts, and unusually for this niche the independent data does not embarrass the claim's direction: Scribbr's comparison measured 68% with zero false positives, the best score among free tools outside the Scribbr-QuillBot family. Per-token verdicts and sentence highlighting show where the model is suspicious rather than issuing one opaque number.

The detector is still a side product. Reports are bare compared with GPTZero's teacher-oriented dashboards, Scribbr's testers found its dual highlighting styles confusing to interpret, and the 2,000-character free cap is the smallest here, under a fifth of what ZeroGPT accepts without even signing up.

ZeroGPT is the checker for a ten-second answer. Paste up to 15,000 characters (roughly 2,000-2,500 words) with no account, no email, no daily wall, an allowance that dwarfs QuillBot's 1,200-word cap and Sapling's 2,000 characters. Pro at $7.99/mo billed annually ($9.99 month-to-month) is also the cheapest paid entry point on this list, raising checks to 100,000 characters with 50-file batch scanning and PDF reports; Max at $18.99/mo annually reaches 150,000 characters.

Temper expectations to match the price. Scribbr's research scored ZeroGPT at 64% with one false positive, and the company publishes no methodology behind its "high accuracy model" language, unlike QuillBot's named RAID evaluation or Turnitin's false-positive documentation. The paid tiers bundle a summarizer, paraphraser, translator and a "ZeroCHAT" chatbot, padding that signals a consumer traffic play more than a detection lab. It is also routinely confused with GPTZero; they are unrelated companies.

Used within those limits it earns its slot: a free, anonymous first pass with the biggest paste box among the well-known names. Treat any "AI-generated" verdict as a prompt to re-check with QuillBot or Originality.ai, not a conclusion.