The best AI detector depends on what you need. GPTZero, Originality.ai and Winston AI are dedicated detectors, while Grammarly and QuillBot include free detectors with usage limits. No detector is fully reliable, and the makers of several of these tools say so themselves, so treat any score as one signal rather than proof.
Below we explain what each tool offers, the free option, the paid prices as shown on the official sites on 20 October 2026, and the accuracy claims each company makes about itself. Those claims are the companies' own and we have not tested them.
Quick comparison
| Tool | Free option | Paid pricing (as shown by the maker) | Its own accuracy claim |
|---|
| GPTZero | Free scans up to 10,000 characters; longer scans need a free account | Not confirmed (see below) | Says it reaches 99.9% accuracy |
| Originality.ai | Free Basic option with daily limits | Pro $14.95 per month; check the official pricing page for higher tiers | Says it is the most accurate detector in third-party studies |
| Winston AI | Free plan with 2,000 credits on a 14-day trial | Essential, Advanced and Elite plans; check the official pricing page for current prices | Says 99.87% accuracy |
| Grammarly AI Detector | Free basic detector | Detailed detector agent is included with Grammarly Pro | Says 99% detection accuracy |
| QuillBot AI Detector | Free: up to 1,200 words per scan, 6 scans per day | Premium removes the limits | Says a 99% detection rate |
A note on reliability
Every figure in the last column of that table comes from the company selling the tool. Several of these companies also cite the same public benchmark, called RAID, and more than one says it ranks first. When more than one company says it ranks first on the same benchmark, that is a good reason to treat vendor numbers with care.
The official sites themselves are cautious about how scores should be used:
- GPTZero says "No AI detector is 100% accurate" and that results "should not be used to punish or as the final verdict".
- Grammarly says no AI detector is 100% accurate, that none can conclusively determine whether AI was used, and that human-written text can be flagged as AI-generated.
- QuillBot says results are probability estimates, not verdicts.
- Originality.ai says scores "reflect probability, not guilt" and should be "one signal, not a final decision".
In practice, use results with care, especially for short texts, heavily edited writing, or anything that could affect a student's grade or a person's job.
GPTZero
What it is: GPTZero is an AI content detector that highlights sentences it thinks are AI-generated and can flag documents that mix human and AI writing. It also offers plagiarism checks, a grammar checker and a hallucination detector. It lists integrations with Chrome, Google Docs, Google Classroom, Canvas and Zapier, plus an API.
Who it suits: Teachers, students and editors who want a detector with sentence-level highlighting and education tools.
Free option: The scan box on GPTZero's home page has a 10,000-character limit. GPTZero says scans over that length need a free account.
Paid pricing: The GPTZero pages we could read showed billing toggles and an upgrade button but no plan names or prices, so we have not listed any. Check GPTZero's own pricing page for current plans.
Its accuracy claims (GPTZero's own): GPTZero claims 99.9% accuracy at telling AI text from human writing. On the RAID benchmark it says it detected 95.7% of AI texts while misclassifying 1% of human texts as AI. It also claims 96.5% accuracy on mixed documents, and says it aims to reduce the false positive rate for English-as-a-second-language writing to 1%.
Originality.ai
What it is: Originality.ai is a content-checking tool. Its main product is an AI detector, alongside a plagiarism checker, a fact and AI hallucination checker, and grammar and readability checkers. It offers a Chrome extension, an API and a Moodle plugin.
Who it suits: People who want to scan written content for AI use and plagiarism.
Free option: The official pricing page shows a free Basic option with no subscription: 3 scans per day, up to 2,000 words per scan, AI detection only.
Paid pricing: Pro is $14.95 per month, or $12.95 per month billed yearly, with 2,000 credits per month. The pricing page also lists an Enterprise plan, but the page shows conflicting figures for it and for how credits are counted, so we have not listed them. Check the official pricing page for current details. Prices are in USD.
Its accuracy claims (Originality.ai's own): The home page calls it "the Most Accurate AI Detector in third-party studies" and reports 97.8% overall accuracy for its multilingual model, citing studies it links to. The company also notes that tools which use AI to rewrite or edit text, including some Grammarly features, can cause false positives, and that shorter text may be less accurate (there is a 100-word minimum).
Winston AI
What it is: Winston AI describes itself as an AI content detector and plagiarism checker. It gives a 0 to 100 score and a sentence-by-sentence assessment, can read text from scanned documents or pictures, even handwriting, and also has an AI image detection product. It lists a Chrome extension and integrations including Google Classroom, WordPress and Zapier.
Who it suits: People who want AI detection and plagiarism checking in one tool.
Free option: The free plan gives 2,000 credits on a 14-day trial, according to the official pricing page.
Paid pricing: The pricing page lists Essential (100,000 credits per month), Advanced (200,000 credits, up to 5 team members) and Elite (500,000 credits, unlimited team members). The page shows two prices for each plan next to a 50% off coupon code, and it does not say clearly which is the standard price, so we have not listed any prices here. Check the official pricing page for current prices.
Its accuracy claims (Winston AI's own): The home page describes a 99.87% accuracy rate. It also says that on the RAID benchmark it detected 99.89% of AI text at a 1% false-positive rate, and reports zero false positives and zero missed AI documents across 8,697 documents on a Chicago Booth benchmark, and says all 25,996 authentic PERSUADE 2.0 essays were recognized as human. These are results on specific test sets from Winston's own page, and they do not guarantee the same result on your text. Winston also notes that detector effectiveness "currently varies".
Grammarly AI Detector
What it is: Grammarly describes its AI detector as free and says it returns a percentage score estimating how much of a text looks AI-generated. It names ChatGPT, Gemini and Claude among the tools it aims to spot.
Who it suits: Anyone who wants a quick free check, and existing Grammarly users.
Free option: The basic detector is free. Grammarly's page does not state word limits or scan quotas.
Paid option: A more detailed detector agent, which highlights specific passages, is included with Grammarly Pro. We have not listed a Pro price because we did not confirm it for this guide.
Its accuracy claims (Grammarly's own): Grammarly says it "achieves 99% detection accuracy" and ranks first on the RAID benchmark. It also says that no AI detector can conclusively determine whether AI was used, that human-written text can be flagged as AI-generated, and that lightly edited AI-generated text may evade detection.
QuillBot AI Detector
What it is: QuillBot's detector gives a score from 0 to 100% and sorts text into entirely AI-written, entirely human-written, or human-written with some AI refinement. Free users get an explainer card describing changes.
Who it suits: Students and writers who want a free check with clear limits.
Free option: QuillBot recommends at least 80 words per scan. Free scans allow up to 1,200 words per scan and 6 scans per day, with 1 free explainer card. Premium removes the word and scan limits. We have not listed a Premium price because we did not confirm it for this guide.
Its accuracy claims (QuillBot's own): QuillBot claims a 99% detection rate, citing evaluations on the RAID benchmark. It says texts of 300 words or more give more reliable scores, that heavily paraphrased or lightly AI-edited content is harder to detect, and that formulaic human writing can score higher than expected. Its page says scores are "signals, not verdicts".
How to use an AI detector sensibly
- Check longer samples where you can. Both QuillBot and Originality.ai say very short text is less reliable.
- Try more than one detector if a result matters, and expect that they may disagree.
- Do not use a score alone to accuse anyone. Several of the makers above advise against it.
- If your own writing is flagged, keep drafts and version history so you can show how the work developed.
How we chose
We picked AI detectors from the tools listed in our directory. We checked each against its official website on 20 October 2026 and only included prices, limits and claims that we could confirm there. Accuracy figures are clearly attributed to the companies that published them. Where a price was not shown clearly, we left it out. Plans change often, so confirm current details on the official pages before you pay.
Frequently asked questions
What is the best AI detector?
There is no single best one. GPTZero, Originality.ai and Winston AI are dedicated detectors with different strengths, and Grammarly and QuillBot offer free detectors with limits. Pick based on your use: classroom checks, web content, or a quick free scan.
Is there a free AI detector?
Yes. GPTZero offers free scans up to 10,000 characters, QuillBot allows up to 1,200 words per scan with 6 scans a day, Grammarly has a free basic detector, Originality.ai has a free Basic option with 3 scans a day, and Winston AI has a free 14-day trial with 2,000 credits.
How accurate are AI detectors?
The companies report high figures, such as 99% or more from several of them, but those are their own claims and are measured on their chosen test sets. The same companies also say no detector is 100% accurate. Use scores with care.
Can an AI detector wrongly flag human writing?
Yes. Grammarly says even human-written text can be flagged as AI-generated, GPTZero says no AI detector is 100% accurate, and QuillBot says formulaic human writing can score higher than expected.
Should a teacher or employer rely on an AI detector score?
Not on its own. Originality.ai says an AI score should not be used alone for academic integrity discipline, GPTZero says results should not be used to punish or as the final verdict, and QuillBot says scores are signals, not verdicts.
Do AI detectors work on text from newer AI models?
Grammarly names ChatGPT, Gemini and Claude among the tools it can identify, and Grammarly and QuillBot both say lightly edited or paraphrased AI text can be harder to catch. We have not tested this ourselves.
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