The short answer
There is no single best AI detector for teachers. If your school has Turnitin, use that, because a teacher cannot buy it alone. If you work on your own, pick a tool that shows a result for each sentence and that you can afford as one person. No detector’s score is proof.
Four things decide which tool fits:
- Does it show the sentences? One number gives you nothing to ask a student about.
- Who has to buy it? Some tools are sold only to institutions. Others a teacher can use alone.
- Does it work inside your LMS? Some do. Ours does not.
- What happens to student work you upload? Vendors say different things. Read the policy.
Comparison table
The tools are in alphabetical order after ours. The order is not a ranking. Each cell is a fact from the vendor’s own site, linked in the sources below. “Not stated” means we read the page and it did not say. Prices are the listed prices in US dollars on that date.
| Tool | Sentence-level evidence | School must buy it? | LMS integration | Cost for one teacher | Document length |
|---|---|---|---|---|---|
| Plagiarism Checker Plus (ours) | Yes. An overall score and a likelihood for every sentence. | No. A teacher can use it alone. | None. There is a Google Docs add-on, a Chrome extension and a REST API. | First check free. A free account includes 3,000 words a month. Personal plan $12.99 a month, or $8.49 a month billed yearly. See pricing. | Up to 1,000 words without an account. At least 50 words. Paid plans allow longer documents. |
| Copyleaks | Their page says sentence-by-sentence insights and highlighted phrases come with a free account. | No for the Personal plan. The Education plan is sold to institutions. | Yes, on the Education plan: Canvas, Moodle, D2L Brightspace, Schoology, Sakai, Edsby and Blackboard. | Up to 25,000 characters per scan free without logging in. Personal plan $16.99 a month, or $13.99 a month billed yearly at $167.88. | At least 255 characters. Up to 2,000 pages on the web platform. |
| Originality.ai | Their page lists Sentence Highlights that show which sentences are most likely AI. | No. An individual can sign up. | Their page lists a Moodle plugin and Google Classroom. | 3 free scans a day without an account. Pro $14.95 a month, or $12.95 a month billed yearly, with 2,000 credits a month. One credit is 100 words of AI checking. | At least 100 words. Up to 2,000 words per free scan. A paid limit is not stated on the pages we read. |
| Turnitin | Their FAQ says the report highlights the text segments the model predicts were written or modified by an AI tool. | Yes. Their help center says it does not sell individual licenses. | Yes. Their page says the AI detector is integrated with your LMS. | Not sold to individuals. | At least 300 words of prose. No more than 30,000 words. |
| Winston AI | Their home page says the AI prediction map gives a sentence by sentence assessment. | No. An individual can sign up. | Their site lists Google Classroom. | A 14-day trial with 2,000 credits. Essential $18 a month and Advanced $29 a month on monthly billing. A 50% discount code was shown when we read the page. | The plan comparison lists up to 200,000 characters per scan. |
| ZeroGPT | Their page says every sentence written by AI is highlighted. | No. The pricing page shows a $0 plan with a sign-up button. | Their FAQ says yes, through its API. It names no LMS. | Paid prices are not stated on the pages we read. | The free box showed a counter of 15,000 characters. A paid limit is not stated on the pages we read. |
Prices and limits change. Before you pay for anything, read the vendor’s own pricing page on the day you buy. Privacy statements and vendor warnings are in their own sections below, because they need more than a table cell.
Sentence-level evidence, not only one number
A single percentage gives you nothing to say to a student. “This essay is 40% AI” ends the conversation. “These three sentences in the conclusion scored high. Tell me how you wrote them” starts one. So the first thing to check is whether a tool shows where its score comes from.
All six tools in the table say they show something below the level of the whole document. The words they use differ:
- Plagiarism Checker Plus (ours) gives an overall score and a likelihood for every sentence.
- Copyleaks describes sentence-by-sentence insights and highlighted AI-written phrases, unlocked with a free account.
- Originality.ai lists Sentence Highlights.
- Turnitin says in its AI writing detection FAQ that the report highlights text segments. It also says no score or highlights are shown when the result is in the 1% to 19% range.
- Winston AI describes a sentence by sentence assessment.
- ZeroGPT says on its home page that every sentence written by AI is highlighted.
A highlighted sentence is still an estimate. It tells you where to read closely. It does not tell you what happened. For how to use it, see how teachers check for AI.
School licence, or on your own?
Start by finding out what your school already has.
If the school must buy it
Turnitin’s help center has a page called Can I purchase an individual Turnitin license? It says Turnitin does not sell individual licenses or single-use subscriptions, and that its services are sold at the institutional level. So you have it or you do not. If you do, its FAQ says only instructors and administrators can see the AI indicator. See does Turnitin detect AI?
Copyleaks also has an Education plan. Its pricing page says the price is based on the number of full-time students at the institution, and you talk to sales.
If you are one teacher
These are the listed costs for one person, read on 10 October 2026.
- Plagiarism Checker Plus (ours). The first AI check is free with no account, up to 1,000 words. A free account includes 3,000 words a month. The Personal plan is $12.99 a month, or $8.49 a month billed yearly, with 200,000 words a month. See pricing.
- Copyleaks. The pricing page lists the Personal plan at $16.99 a month, or $13.99 a month billed yearly at $167.88. One credit covers up to 250 words.
- Originality.ai. The pricing page lists Pro at $14.95 a month, or $12.95 a month billed yearly, with 2,000 credits a month. It says one credit is used for a 100-word AI check. The free tool allows 3 scans a day of up to 2,000 words.
- Winston AI. The pricing page lists a Free plan with 2,000 credits for a 14-day trial, then Essential at $18 a month and Advanced at $29 a month on monthly billing. A 50% discount code was shown on the page when we read it.
- ZeroGPT. The pricing page shows a $0 plan. The paid plan details did not load in the page we read, so we list no price.
Before you sign up on your own, ask whether your school allows it. Many schools have rules about which outside services may receive student work.
LMS integration
An integration means the check runs where students hand in work, so you do not copy and paste each paper. In most cases the school sets it up, not the teacher.
- Turnitin. Its AI writing page says the AI detector is integrated with your LMS.
- Copyleaks. Its pricing page lists Canvas, Moodle, D2L Brightspace, Schoology, Sakai, Edsby and Blackboard under the Education plan. It says to contact sales for LMS integration.
- Originality.ai. Its AI checker page lists a Moodle plugin and Google Classroom for teachers and students.
- Winston AI. Its home page lists Google Classroom among the places it works.
- ZeroGPT. Its FAQ asks “Do you integrate with LMS or enterprise systems?” and answers yes, through its API. It names no LMS.
- Plagiarism Checker Plus (ours). We do not integrate with any LMS. You paste text into the web app, or use the Google Docs add-on or the Chrome extension. If you need the check inside Canvas, Moodle or Google Classroom, our tool is not the one for that.
Privacy of student work
A student’s essay is the student’s work, and it often has their name on it. Before you upload one, read what the vendor says it does with it. Below is only what each vendor’s own privacy or help page says. We did not check whether any vendor does what it says.
| Tool | What the vendor’s own page says |
|---|---|
| Plagiarism Checker Plus (ours) | Text you check is used to run the check. It is never used to train AI models. |
| Copyleaks | Its privacy policy says that in certain regions it uses the content of scans to improve its products, after it filters out direct identifiers. It says a direct customer can opt out of the use of their information to train its models by contacting customer support. For institutions, it says it acts as a “School Official” under FERPA and uses education records only as the institution directs. |
| Originality.ai | Its AI checker page says text put into the free AI detector may be used for training, and that users with an account can opt out. Its privacy policy has a section on Student Data for school customers. It says it does not sell Student Data or use it for targeted advertising, and does not use it to train its AI models so long as the customer has chosen to opt out of training. |
| Turnitin | Not stated on the pages we read. We did not read Turnitin’s privacy policy for this page. |
| Winston AI | Its education page asks “Does Winston AI store or train on student work?” and answers that it does not use submitted content to train or improve its models, and that users can purge their data. Its privacy policy says it does not use submitted content to build or train AI models without explicit, opt-in consent, and that deleted content may stay in encrypted backups for up to 90 days. |
| ZeroGPT | Its FAQ says text you check is not saved, shared, published online or used to train its AI detection model. Its privacy policy says it does not use private user content to train AI models. |
Two practical steps help with any tool. Remove the student’s name before you paste. And check your school’s rules on sharing student work with outside services before you start.
What the vendors themselves warn
An AI score is a probability, not proof. It should never be the only basis for an academic integrity decision. Several vendors say the same about their own tools:
- Turnitin. Its FAQ says the percentage “should not be used as the sole basis for action or a definitive grading measure by instructors”. It says Turnitin does not make a determination of misconduct.
- Originality.ai. Its AI checker page says “An AI score shouldn’t be used alone for academic integrity discipline”, and that scores reflect probability, not guilt.
- Winston AI. Its education page says to use detection results as one part of a fair review workflow, and that educators should combine the result with writing history, source review and a conversation with the student.
- ZeroGPT. Its FAQ says to pair the detector with plagiarism checks and clear classroom policies, and to use signals as evidence within a fair review process.
- Copyleaks. Not stated on the pages we read.
- Plagiarism Checker Plus (ours). We say it on every page: the score is a reason to talk to the student, never a verdict. We publish no accuracy figure.
Vendors also publish accuracy claims. Copyleaks says on its site that its detector has over 99% accuracy. Turnitin states a false positive rate of less than 1% for a document. Originality.ai says its multilingual model has an overall accuracy of 97.8%. ZeroGPT’s home page shows 98.4%. These are the companies’ own measurements of 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. The authors found the tools both flagged human writing and missed AI writing. The study is from 2023, and the tools have changed since. Our guide do AI detectors work? covers the research, including the higher error rate found for writers working in a second language.
A note on Google Classroom
Many teachers already have a checking tool and do not know what it covers. Google Classroom’s built-in tool is called originality reports. Google’s help page Turn on originality reports says the reports compare a student’s files against web pages and books. Google’s documentation describes no AI-writing score.
So originality reports are a plagiarism check, not an AI check. A clean originality report says nothing about whether a text was written with AI. We go through what the reports do and what teachers can see in can Google Classroom detect AI?
A fair-use checklist for teachers
Whichever tool you use, these steps keep the process fair.
- Tell students first. Say in the assignment what AI use is allowed, and that work may be checked with a detector.
- Check your school’s rules. Find out which tools you may upload student work to, and what the integrity policy says counts as evidence.
- Take the name off. Remove the student’s name and ID before you paste text into an outside tool.
- Check enough text. A short answer gives a detector little to measure. Do not act on a result for a few sentences.
- Read the sentences, not the total. Look at which passages were flagged and where they sit together.
- Give extra care to known weak spots. Formulaic writing and writing in a second language are flagged more often. Give the score less weight there.
- Look for other evidence. Drafts, version history, notes and the student’s earlier work show how a text was produced. A detector cannot.
- Talk before you conclude. Ask the student how they wrote the flagged passages. Listen to the answer. See talking to a student about plagiarism.
- Never decide on the score alone. A score is a probability. It is not proof, and it should never be the only basis for a decision.
- Write down what you did. Keep a note of what you saw, what the student said and which policy you followed.
For the wider process, see how do teachers check for AI? To try a sentence-level check on one paper, see our AI detector for teachers.
What we do not know and did not test
- Accuracy. We did not run the same papers through each tool. We do not know which detector is right more often, or which flags more human writing. This page makes no claim about that.
- What each report looks like in use. We read the vendors’ pages. We did not sign up for each tool and run a paper through it.
- How each integration works. We did not install any LMS integration. We report only that the vendor lists it.
- Turnitin’s privacy terms and price. We did not read its privacy policy for this page, and it publishes no price for individuals because it does not sell to them.
- ZeroGPT’s paid prices. The plan details did not load in the page we read.
- Copyleaks’ Education price. It is set by sales, based on student numbers.
- Paid document limits for Originality.ai and ZeroGPT. The pages we read do not state them.
- Whether vendors do what their policies say. We quote the policies. We did not audit anyone.
- Other detectors. There are more tools than these six. Leaving one out is not a judgement about it.
- What happens after today. Vendors change limits, prices and policies. 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 its limits are listed above, including that it has no LMS integration, and why we do not name a winner.
Sources
Each vendor’s own website. Facts checked on 10 October 2026.
- Copyleaks: AI detector, pricing and privacy policy.
- Originality.ai: AI checker, pricing and privacy policy.
- Turnitin: AI writing detection capabilities FAQ, Can I purchase an individual Turnitin license? and AI writing page.
- Winston AI: home page, pricing, education page and privacy policy.
- ZeroGPT: home page, FAQ and privacy policy.
- Google Classroom: Turn on originality reports.
- 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, AI detector for teachers and pricing pages.