The short answer
There is no single best free AI detector. The free tiers differ most in size. Copyleaks lists 25,000 characters per scan without logging in. ZeroGPT’s box shows 15,000 characters. Originality.ai allows 2,000 words, three times a day. QuillBot and Scribbr allow 1,200 words per check. Plagiarism Checker Plus gives a first check of 1,000 words.
Size is only one thing to look at. Three more matter:
- Do you have to sign up? Some tools work at once. Some ask for an account first.
- Do you see which sentences were flagged? One number tells you little. A result for each sentence shows where the score comes from.
- What happens to your text? Policies differ. One maker says text pasted into its free tool may be used for training.
Free limits compared
The tools are in alphabetical order after ours. The order is not a ranking. Each cell is a fact from the maker’s own site, linked in the sources below. “Not stated” means we read the page and it did not say. Some makers count characters and some count words. As a rough guide, 1,000 English words is about 6,000 characters.
| Tool | Free limit per check | How many free checks | Sign-up needed | Sentence-level results | Languages |
|---|---|---|---|---|---|
| Plagiarism Checker Plus (ours) | Up to 1,000 words. The AI check needs at least 50 words. | The first check without an account. A free account includes 3,000 words a month. | Not for the first check. | Yes. An overall score and a likelihood for every sentence. | The web app and the reports are in English. |
| Copyleaks | Up to 25,000 characters per scan without logging in. At least 255 characters. | Not stated for scans without logging in. A free account gives “more monthly credits”. The number is not stated. | Not for a scan. Yes for the detailed view. | Their page says sentence-by-sentence insights unlock when you sign up for a free account. | Over 30 languages. |
| Grammarly | Not stated on the pages we read. | Not stated on the pages we read. | Not stated on the pages we read. | The free tool shows a percentage. Their page says the AI Detector agent in Grammarly Pro shows which parts may sound AI-generated. | Not stated on the pages we read. |
| Originality.ai | Up to 2,000 words per scan. At least 100 words. | 3 scans a day. | No. Their page says the 3 daily scans need no account. | Their page lists Sentence Highlights as a feature. It does not say whether the free scan includes them. | 30 languages. |
| QuillBot | Up to 1,200 words per scan. At least 80 words. | Up to 6 scans a day. | Not stated on the page we read. | Their page describes sentence-level highlights. The free tier includes 1 explainer card that says why text was flagged. | Over 20 languages. |
| Scribbr | Up to 1,200 words per submission. | Unlimited, their page says. | No. Their page says you do not have to create an account. | Their page describes paragraph-level feedback that points to the areas likely to be AI-generated or AI-refined. | English, German, French and Spanish. |
| Winston AI | The Free plan is listed as 2,000 credits for a 14-day trial. The page we read does not state a limit per check for that plan. | A 14-day trial with 2,000 credits, not a free tier that renews. | Yes. Their home page says to sign up first, and that sign-up is free. | Their home page says its AI prediction map gives a sentence by sentence assessment. | Nine languages are listed on the pricing page, including English, Spanish and German. |
| ZeroGPT | The box on the home page showed a counter of 15,000 characters when we opened it. | Not stated on the pages we read. | Not stated on the pages we read. | Their page says every sentence written by AI is highlighted. | Their FAQ says all available languages are supported. |
Limits change often. Before you rely on one, read the maker’s own page on the day you use it.
What each free tier gives you
The same facts as the table, with a little more detail and the page each one came from.
Plagiarism Checker Plus (ours)
Our AI detector gives an overall score and a likelihood for every sentence. The first AI check is free with no account, up to 1,000 words. A free account includes 3,000 words a month. The same report can include a plagiarism check, with every match linked to its source. There is a Google Docs add-on, a Chrome extension and a REST API.
Its limits:
- The free check stops at 1,000 words. That is smaller than several tools in the table.
- After the first check you need a free account.
- The web app and the reports are in English.
- We publish no accuracy figure.
- An AI score is a probability. It is not proof.
Copyleaks
The Copyleaks AI detector page says you can scan up to 25,000 characters without logging in. It says a free account unlocks sentence-by-sentence insights and highlighted phrases, and more monthly credits for scans. The page does not say how many credits. It lists over 30 supported languages and a minimum of 255 characters on the web platform.
Grammarly
Grammarly’s AI detector page has a box where you paste text or upload a document. It says you see what percentage of your text appears to be AI-generated. It also says the AI Detector agent in Grammarly Pro goes beyond a score and shows which parts may sound AI-generated. The page does not state a word limit, a number of checks, a language list or whether you must sign up. Grammarly’s AI Detector user guide says the percentage should not be used as an objective source of truth.
Originality.ai
The Originality.ai AI checker page says you can check up to 2,000 words and run up to 3 free scans a day without an account. It says there is no free trial of the full product, only this limited free tool. It states a 100-word minimum and 30 supported languages. Its pricing page lists the Free plan as AI detection only. The same AI checker page says that text put into the free detector may be used for training, and that users with an account can opt out.
QuillBot
QuillBot’s AI detector page has a table of free and Premium features. Free is up to 1,200 words per scan, up to 6 scans a day and 1 explainer card. The page says at least 80 words are needed to scan, and that texts of 300 words or more give more reliable scores. It says the detector supports over 20 languages. It does not say whether a free scan needs an account.
Scribbr
Scribbr’s AI detector page says you can run an unlimited number of AI checks for free, up to 1,200 words per submission, without creating an account. It says the detector tells apart human-written, AI-generated and AI-refined text, gives feedback at the paragraph level, and analyzes English, German, French and Spanish. The page also says “we do not store or share your data”. It mentions a Premium AI Detector. We did not read a price for it.
Winston AI
Winston AI’s pricing page lists a Free plan with 2,000 credits for a 14-day trial. So it is a trial, not a free tier that renews. The home page says to sign up first and that signing up is free. It says the AI prediction map gives a sentence by sentence assessment. The pricing page lists English, Spanish, Chinese (Simplified), German, Polish, Portuguese, Italian, Ukrainian and Dutch.
ZeroGPT
The box on the ZeroGPT home page showed a counter of 0/15,000 characters when we opened it. The page says every sentence written by AI is highlighted, with a gauge that shows the percentage of AI in the text. Its FAQ says all available languages are supported, and that text you check is not saved, shared, published online or used to train its detection model. The pricing page shows a plan at $0 with a sign-up button. The pages we read do not state how many free checks you get or whether the home page box needs an account.
What is behind payment
A free tier is a sample. This is what each maker’s page lists as paid. Prices are the listed prices in US dollars on 10 October 2026.
| Tool | What the paid plan adds | Listed price |
|---|---|---|
| Plagiarism Checker Plus (ours) | More words a month, longer documents and API access. | Student plan $4.99 a month, or $3.99 a month billed yearly. See pricing. |
| Copyleaks | AI and plagiarism in a single report, the AI Logic explanations, saved scans, a browser extension and a Google Docs add-on. One credit covers up to 250 words. | Personal plan $16.99 a month, or $13.99 a month billed yearly at $167.88. |
| Grammarly | The AI Detector agent, which shows which parts may sound AI-generated. Their support page calls AI detection inside the Grammarly product a paid feature. | Not stated on the pages we read. |
| Originality.ai | More words and scans, plagiarism checking and the other tools. Pro includes 2,000 credits a month. One credit is 100 words of AI checking. | Pro $14.95 a month, or $12.95 a month billed yearly. |
| QuillBot | No word limit for detection scans, unlimited scans, unlimited explainer cards, and downloading and sharing the full report. | Not stated on the page we read. |
| Scribbr | A Premium AI Detector is mentioned on the page. | Not stated on the page we read. |
| Winston AI | Monthly credits after the trial. Essential includes 100,000 credits a month. Advanced includes 200,000. | Essential $18 a month and Advanced $29 a month on monthly billing. A 50% discount code was shown on the page when we read it. |
| ZeroGPT | The home page has a “Get premium features” link. The plan details did not load in the page we read. | Not stated on the pages we read. |
Before you pay for anything, read the maker’s own pricing page on the day you buy.
What no free detector can do
This applies to every tool on this page, paid or free, ours included.
- It cannot prove who wrote a text. A detector reads the words and estimates how likely it is that a language model produced them. It has no record of how the text was written. QuillBot’s page says this directly: its detector cannot verify whether a piece of writing was created by a human.
- It cannot be right every time. A detector can flag text a person wrote, and it can miss text an AI wrote. Grammarly’s page says no AI detector is 100% accurate and that you should never rely on the results of an AI detector alone.
- It cannot predict another tool’s result. Each detector is built and trained differently. A result from one does not tell you what your school’s or client’s tool will show.
- It cannot judge short text well. A few sentences give it little to measure. That is why these tools set a minimum length.
Several of these makers publish accuracy figures. Copyleaks says on its site that its detector has over 99% accuracy. Grammarly’s page says 99% detection accuracy. QuillBot’s page says a 99% detection rate. ZeroGPT’s home page shows 98.4%. These are the makers’ own claims about their own products. We did not test them. Independent research points the other way: a 2023 study by Weber-Wulff and colleagues tested 14 detection tools and concluded that they were neither accurate nor reliable. Every tool in that study scored below 80% accuracy. The study is from 2023, and the tools have changed since then. Our guide do AI detectors work? goes through the research, so we will not repeat it here.
How to read a score
An AI score is a probability, not proof. It should never be the only basis for an academic integrity decision. Read it like this:
- Start with the sentences, not the total. Look at which lines were flagged. A few flagged lines spread through a long text mean something different from whole flagged paragraphs.
- Check the length. A result for 100 words is much less steady than a result for 1,000.
- Think about the kind of writing. Formulaic text, such as definitions and set-format answers, is flagged more often. So is writing by people working in a second language. See AI detector false positives.
- Do not compare numbers across tools. Each tool calculates its percentage in its own way.
- Use it as a reason to look closer. If the text is yours, keep your drafts and notes. If you are reviewing someone else’s text, talk to the writer before you decide anything.
If you were flagged for work you wrote yourself, see how to prove you didn’t use AI. For what a given number means, see what percentage of AI is acceptable? For how the scoring works, see how AI detectors work.
How to choose
Ask these questions in this order.
- How long is my text? Count the words. Compare that with the free limit per check in the table.
- How many texts will I check? One essay fits most free tiers. A daily habit needs a tool with a daily or monthly allowance.
- Am I willing to sign up? If not, look at the tools that say no account is needed.
- Do I need to see the sentences? If you want to know where a score comes from, pick a tool whose free result shows it.
- What language is my text in? Check the maker’s language list.
- What happens to my text? Read each tool’s privacy policy before you paste anything private. We can only speak for our own tool: text you check with Plagiarism Checker Plus is never used to train AI.
If you are a teacher, the questions are different. See best AI detectors for teachers.
What we do not know and did not test
- Accuracy. We did not run the same texts through each tool. We do not know which detector is right more often. This page makes no claim about that.
- What each free result really shows. We read the makers’ pages. We did not sign up for each tool and run a text through it. A page can say “sentence-level” while the free result shows less.
- Grammarly’s limits. The pages we read state no word limit, no number of checks, no language list and no sign-up rule for the free tool. We also did not read a price.
- ZeroGPT’s plans. The plan details on its pricing page did not load in the page we read. We do not know its paid prices, how many free checks it allows or whether an account is needed.
- Prices for QuillBot and Scribbr. Neither AI detector page states one.
- Copyleaks’ free account allowance. The page says “more monthly credits” and gives no number.
- Winston AI’s free limit per check. The pricing page states the trial credits, not a per-check limit for the Free plan.
- Other detectors. There are more tools than these eight. Leaving one out is not a judgement about it.
- What happens after today. Makers change limits and prices. This page shows what we could read on 10 October 2026.
We also have an interest here: we would like you to try our tool. That is why the limits of our own detector are listed above, and why we do not name a winner.
Sources
Each maker’s own website. Facts checked on 10 October 2026.
- Copyleaks: AI detector and pricing.
- Grammarly: AI detector and AI Detector user guide.
- Originality.ai: AI checker and pricing.
- QuillBot: AI detector.
- Scribbr: AI detector.
- Winston AI: home page and pricing.
- ZeroGPT: home page, FAQ and pricing.
- Research: Weber-Wulff et al., 2023, Testing of detection tools for AI-generated text, International Journal for Educational Integrity.
- Plagiarism Checker Plus: our own AI detector and pricing pages.