GPTZero
GPTZero is an AI text detector that flags machine-written passages at document, paragraph and sentence level, and bundles plagiarism, hallucination and grammar checks. Free scans need no account, and a documented API serves developers.
What is GPTZero?
GPTZero is an AI content detector: paste or upload a text and it estimates how much of it was produced by a large language model, then shows you where. Founded in January 2023 by Edward Tian and Alex Cui, it claims 17 million users, a million educators, and use across more than 3,500 colleges and 100-plus organisations in education, hiring, publishing, legal work and data labelling.
The engine is proprietary and built from seven components. Rather than a single verdict it returns a trinary classification — HUMAN_ONLY, MIXED or AI_ONLY — with a probability for each class and a confidence band of high, medium or low. Sentence-by-sentence highlighting shows which passages drove the result. The published figures are a 99% accuracy claim, 96.5% on documents mixing human and AI writing, and a false-positive rate under 1%; the independent RAID benchmark reported 95.7% of AI texts caught for 1% of human texts misflagged, rising above 99% on modern models. A research partnership with Penn State's AI Research Lab backs the work, alongside an arXiv paper and the first sentence-highlighting model built on hidden Markov models.
Two engineering choices stand out. Paraphraser Shield targets the usual evasion tricks, rewording and homoglyph substitution. And the model is deliberately de-biased for writers using English as a second language, with false positives on TOEFL essays reported down to 1.1%.
Around the detector sits a wider authenticity suite: a plagiarism checker, a hallucination detector, AI Vocabulary, a citation and fact checker drawing on 220 million scholarly articles and news items, a grammar tutor, expert feedback, AI Vision for social media, and Writing Replay, which reconstructs how a document was typed so an author can prove the work is theirs. Input accepts pasted text, docx, pdf and image files, in batches.
Access is free without an account up to 10,000 characters, and the product reaches into Chrome, Google Docs, Canvas, Google Classroom, Zapier and a v2 API. In June 2026 GPTZero announced it plans to join Superhuman, saying nothing changes for daily users.
What it does
- Detect AI-generated text at document, paragraph and sentence level
- Name the likely source model, from ChatGPT and GPT-5 to Gemini, Claude, Llama and Deepseek
- Explain in plain language why a passage reads as machine-written
- Check the same text for plagiarism against outside sources
- Flag hallucinated claims and surface citable sources that support or contradict them
- Replay how a document was actually written, as evidence of human authorship
- Deliver all of it through an API, a Chrome extension, or Canvas and Google Classroom
When to use GPTZero / When not to
A quick filter to help you decide if GPTZero is the right fit.
When to use GPTZero
- Teachers and school administrators who want to open a conversation about academic integrity rather than hand down a verdict
- Universities and colleges wiring AI detection into Canvas or Google Classroom for whole cohorts
- Newsrooms and fact-checking desks verifying submitted copy, as AP Verify and NewsGuard already do
- Recruiters and HR teams screening application material that may have been drafted by a language model
- Developers who want the same detection engine behind an API call rather than a web form
When not to use GPTZero
- Anyone looking for proof: the publisher states results must not be used to punish or as a final verdict
- Reviewers working on very short snippets, where sentence-level accuracy is weakest
- Teams writing outside English, German, Portuguese, French or Spanish, the only fully supported languages
- Organisations bound by HIPAA, FISMA or GLBA, which the terms of use exclude outright
- Users who need a mobile or desktop application, since only web, browser and API access exist today
How to use GPTZero
A typical end-to-end flow, from setup to results.
- Open the detector on the home page — no account is needed for the first 10,000 characters
- Paste your text, or upload a docx, pdf or image file
- Press Scan and read the overall AI score
- Work down the sentence-level highlights to see which passages triggered it
- Check the confidence band before drawing any conclusion from the result
- Switch to Advanced Scan for the detailed class probabilities
- Create a free account to raise the limit to 150,000 characters, or a batch of 250 files
- Install the Origin Chrome extension to scan any page, Gmail or Google Docs in one click
- Connect Canvas or Google Classroom to scan submitted assignments where they already sit
- Call the v2 API with an x-api-key header to automate detection at scale
Pros & Cons
Pros
- Accuracy claims are unusually well supported, resting on the independent RAID benchmark and university labs rather than internal testing alone
- It explains in plain language why a passage reads as AI, instead of returning a bare score
- Deliberately de-biased for second-language writers, with false positives on TOEFL essays reported at 1.1%
- Genuinely usable for free: 10,000 characters with no account at all, 150,000 with a free one
- SOC 2 and FERPA credentials make it defensible for schools and universities
- Content sent through the API is not stored by default and not used for product improvement
- Entry price of USD 9.99 per month, falling 45% on an annual commitment
Cons
- No AI detector is reliable enough to stand on its own, and GPTZero says so itself
- Accuracy drops on short texts and is weakest at sentence level
- Only five languages are fully supported: English, German, Portuguese, French and Spanish
- Dashboard inputs are stored and used in aggregate, unlike API traffic, with no documented way to opt out
- No data processing agreement is published, no subprocessor list exists, and no Article 27 EU representative is named
- The legal name differs between documents: GPTZero LLC in the terms, GPTZero Inc. in the privacy policy
- No mobile or desktop application, and the roadmap now depends on the Superhuman integration
Pricing & Plans
A permanent free plan is available: the detector runs without an account up to 10,000 characters, and a free account raises that ceiling to 150,000 characters or a batch of 250 files. Paid subscriptions start at USD 9.99 per month for the Essential plan, or USD 99.96 per year, annual billing being advertised as a 45% saving. New subscribers are offered a 14-day free trial.
- Free — AI detection without an account up to 10
- 000 characters
- or 150
- 000 characters and 250 files with a free account
- 150
- 000 words a month
- Basic AI Scan
- premium detection models
- plagiarism scanning and grammar feedback
- 300
- 000 words a month
- adding Advanced AI Deep Scan
- multilingual detection and downloadable AI reports
- 500
- 000 words a month
- adding 10 million words of overage
- 250-file scanning
- page-by-page detection and enterprise-grade LMS security
- Team and Enterprise — everything in Professional for every seat
- with shared credits and unified billing
- priced through the sales team
- API — billed separately
- volumes above 5 million words a month are handled by the sales team
Data, GDPR & hosting
A consolidated view of how GPTZero handles your data.
GDPR overview
Implementation is partial but genuine. The privacy notice, in force since 2 April 2026, carries a section addressed explicitly to EU and UK users, sets out the legal bases it relies on — consent, legitimate interests, legal obligations and vital interests — and grants access, copy, rectification, erasure, restriction, portability, objection and freedom from automated decision-making. Consent can be withdrawn at any time, requests run through a data subject access form, and complaint routes name the Member State authority, the UK ICO and the Swiss federal commissioner. A Data Protection Officer is designated and reachable by email and by post. Two gaps stand out: no representative is appointed under Article 27, and the site never states in so many words that it is GDPR compliant.
Who owns the data?
The terms leave you responsible for everything you transmit and disclaim any liability for its loss or corruption, while a contribution licence covers material you post. What matters more is the split by surface: content sent through the API is not stored by default and not used for product improvement, and subscribers may opt in to storage only so they can re-read it inside the application. Dashboard inputs, by contrast, are kept and exploited in aggregate to improve the service. Payment details are handled by PayPal and Stripe. GPTZero states it neither processes sensitive personal information nor collects information from third parties.
Reuse rights
Nothing in the terms restricts what you do with a scan you have run: the report, the AI score and the sentence-level highlights are yours to keep, quote or file, and no permission is required. GPTZero even publishes a citation format, which invites academic reuse of its results. The constraint sits elsewhere. The site itself, its source code, designs, text and marks are proprietary and may not be copied, reproduced or redistributed, and the terms bar use of the service for commercial endeavours that have not been specifically approved. In practice you may use your own results freely, but you may not resell access to the detector or repackage the product around them.
Data retention & training
Hosting summary
The terms of use state plainly that the site is hosted in the United States, and that accessing it from anywhere else means consenting to the transfer and processing of your data there. No other jurisdiction is named, and the site never describes a broad hosting region such as the EU or APAC. The security posture rests on two attestations: AICPA SOC 2, cited on the developer, integrations and sales pages and covering security, availability, processing integrity, confidentiality and privacy; and FERPA, cited for the education market. The front end is served through Cloudflare, whose anycast addressing means the resolved IP says nothing about where data actually sits. What is missing matters as much as what is present. GPTZero publishes no list of subprocessors, so the third parties touching user data cannot be enumerated from the site — only PayPal and Stripe are named, and only for payment handling. No data processing agreement is published or offered on request. An institution moving student or candidate work through the service should ask for both in writing before signing.
Things to keep in mind
Risks and trade-offs to weigh before adopting GPTZero.
- Treating a probability as a verdict: an accusation built on a score alone can damage a student or a candidate who did nothing wrong
- Automation bias — once a tool reports 99%, people stop reading the text themselves, which is the opposite of what the publisher recommends
- Second-language and neurodivergent writers still carry a higher risk of being misflagged, even after the de-biasing work
- An arms race: paraphrasers and homoglyph tricks keep evolving, and any detector is briefly behind them
- Dashboard submissions are retained and used in aggregate, so pasting confidential or third-party text carries a cost you may not have priced
- A chilling effect on writing itself, as authors flatten their own style to avoid tripping a detector
- Thin legal paperwork — no DPA, no subprocessor list, no EU representative — leaves an institution exposed when submissions contain personal data
Setup & Integrations
Technical difficulty
Trivial for a single user: open the home page, paste a text, press Scan. No account, no install, no configuration. The Chrome extension is a one-click install and the Google Docs report needs nothing more. Connecting Canvas or Google Classroom is an administrative task rather than a technical one — GPTZero describes it as easy implementation and offers a call with an expert. The API is a single POST with an x-api-key header, with ready-made examples in 17 languages, and Zapier workflows need no code at all.
Deployment
Integrations
Supported languages
Behind GPTZero
Fundraising
Social
Resources
All the official URLs gathered for verification and reference.
Frequently asked questions
Does GPTZero only detect ChatGPT?
How accurate is it?
Can I use it for free?
What does a paid plan cost?
Which languages are fully supported?
Is my text used to train the model?
How long is my data kept?
Is there an API?
What is the minimum age?
Can a GPTZero result prove that a student cheated?
Should you pick GPTZero?
GPTZero is the reference point in AI detection, and it earns that position on more than reach. The trinary classification, the confidence bands and the sentence-level highlights give a reader something to argue with, which is exactly what a probabilistic verdict should offer. The de-biasing work for second-language writers is documented and quantified rather than asserted, and the independent RAID benchmark carries more weight than the marketing figure printed beside it.
The most useful thing the company does is warn against its own output. Results, it says, should not be used to punish or treated as a final verdict — and that framing, backed by Writing Replay and the wider authenticity suite, is what makes the tool defensible in a classroom.
The reservations are mostly contractual. No data processing agreement is published, no subprocessor list exists, and no Article 27 representative is named even though the privacy notice invokes the GDPR at length. Dashboard inputs are retained and used in aggregate with no documented opt-out, while API traffic is excluded by default — a split worth understanding before choosing a surface. The legal name is inconsistent across the company's own documents, and the published address is a mailbox rather than an operating office.
Then there is the acquisition. GPTZero announced in June 2026 that it plans to join Superhuman, promising that nothing changes for daily users. That may well hold, but anyone signing an institutional contract should read it knowing the counterparty is moving.
For an individual the calculus is simple: the free tier is real and the entry price is low, so the tool costs nothing to evaluate. For an institution the product is strong and the paperwork is thin — ask for the DPA before you commit.
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