GPTZero review
- Made by
- GPTZero, owned by Superhuman (Grammarly's parent) since June 2026
- Launched
- 3 January 2023, by Princeton student Edward Tian
- Free plan
- Yes: 10,000 words a month
- Paid plans from
- $12.99/month billed yearly (Premium); $23.99 monthly
- Platforms
- Web, Chrome extension, Google Docs, Word add-in, Canvas, Google Classroom, API
- Languages
- English plus 20+ others, including Spanish, French, German and Chinese
- Users
- 17 million+ (company claim)
GPTZero checks a piece of writing and estimates whether a person, an AI chatbot or a mix of both wrote it. You paste text or upload a file, and it returns a verdict, a confidence level and highlighted sentences. It was built by a Princeton student in January 2023, grew into one of the most-used detectors in schools, and was bought by Superhuman, Grammarly's parent company, in June 2026.
It ranks #2 in our best AI detectors and #2 in our AI detectors for teachers. This review looks at the evidence on accuracy, the risk of false accusations, the free plan's limits, and what real users say.
GPTZero is a good first check, especially for teachers, because independent testing found it careful about wrongly flagging human writing. Its weak spot is AI text that has been run through a humanizer tool: it missed about half or more of that in the main 2025 study. Use the free plan to test it; pay for Premium only if you need plagiarism checks or more words. For the strongest detection, Pangram tested better.
Score breakdown
Best for
- Teachers who want a free, cautious first check on student work
- Educators who want writing replay in Google Docs as process evidence
- Students checking their own work before a school detector sees it
- Developers who need an AI-detection API with published per-word pricing
Skip it if
- Catching AI text that has been deliberately disguised with humanizer tools
- Making misconduct decisions from a score alone
- Short answers of a few sentences, where every detector is unreliable
What we like
- Careful with human writing in the October 2025 University of Chicago study
- Useful free plan: 10,000 words a month with sentence highlights
- Writing replay shows how a Google Doc was typed, pasted and edited
- Clear verdicts with confidence levels, including a "mixed" category
- Canvas, Google Classroom, Word and API integrations
Watch out for
- Missed about half or more of humanized AI text in independent testing
- Plagiarism checks and bypasser detection need a paid plan
- Low Trustpilot score driven by false-flag and billing complaints
- The company's own accuracy claims are hard to verify independently
Key features, explained
AI detection with highlights
Paste text or upload a file and GPTZero labels it as human, AI or mixed, then highlights the sentences that pushed the result. Each verdict carries a confidence category (high, moderate or uncertain). GPTZero says its error rate is under 1% when confidence is high. It checks text from ChatGPT, Claude, Gemini, Llama and other models, and works in English plus more than 20 other languages. Free users can scan up to 10,000 characters at a time.
Advanced Scan and bypasser detection
Advanced Scan gives a more detailed sentence-by-sentence breakdown. Free users get one, Premium and Professional get unlimited use. Paid plans also add an AI Vocabulary scan, which spots words chatbots overuse, and detection of text that was paraphrased or run through an AI bypasser, the tools sold to make chatbot writing look human. Independent results suggest this is where GPTZero is weakest, so treat a clean result on edited text with care.
Writing replay
GPTZero's Chrome extension adds it to Google Docs. The Writing Report replays how a document was written, shows large pastes and bursts of typing, flags unusual typing patterns and, for shared documents, estimates how much each editor contributed. For teachers, this process evidence is often more useful than an AI score. For students, it is a way to prove authorship. Remember that tools which simulate human typing exist, so a replay is evidence, not proof.
Plagiarism and citation checks
Premium and Professional add a plagiarism checker, downloadable AI reports and a source tool that finds references and generates citations. GPTZero also checks bibliographies for citations that look invented, a common sign of unedited chatbot output, and flags uncited claims. This makes it a broader writing-integrity tool than a pure AI detector, although its plagiarism database is not comparable to Turnitin's archive of past student papers.
Classroom and developer integrations
Teachers can run GPTZero inside Google Docs and Google Classroom, and the Professional plan adds Canvas and Google Classroom integration with team roles and shared billing. There is also a Microsoft Word add-in, a Zapier connection and an API that returns document-level labels, probabilities and sentence highlights. GPTZero says it does not store documents sent through the API, unlike text pasted into its website.
Where GPTZero ranks
Our scores come from our category rankings, where each tool is scored 0–10 on weighted criteria against its rivals.
| Ranking | Listed as | Position | Score |
|---|---|---|---|
| Best AI Detectors | GPTZero | #2 of 9 | 7.8 |
| Best AI Detector for Teachers | GPTZero | #2 of 8 | 8.2 |
What users say about GPTZero
Opinions split sharply depending on who is reviewing. GPTZero's Chrome extension, which runs it inside Google Docs, scores 4.7 out of 5 from 731 ratings. Trustpilot is much harsher at 2.2 out of 5 from 140 reviews, with the ratings split between five stars and one star. Teacher comments collected on GPTZero's own site praise writing replay, the clear highlights and the free allowance, so treat them as hand-picked. The one-star reviews mostly come from people who say their own writing was flagged as AI, including formal academic prose, and from subscribers who report trouble cancelling or charges after cancelling. A few mention lag and slow support. That pattern matches the independent evidence: GPTZero is careful, but no detector is safe to use as the only proof.
Users praise
- Writing replay gives teachers evidence beyond a single score
- Generous free allowance for occasional checks
- Sentence highlights make it clear which parts drove the verdict
- Works inside Google Docs and Classroom without extra steps
Users complain about
- Human writing, especially formal or academic text, flagged as AI
- Difficulty cancelling and charges after cancellation
- Lag, crashes and slow support replies
- Confident-looking scores that users feel are not justified
| Review site | Rating | Reviews | Checked |
|---|---|---|---|
| Chrome Web Store | 4.7/5 | 731 | 2026-09 |
| Trustpilot | 2.2/5 | 140 | 2026-09 |
Ratings are third-party aggregates and change over time. They are context, not part of our score.
GPTZero has a free plan and two paid plans for individuals. Free scans 10,000 words a month. Premium costs $23.99 a month, or $12.99 a month billed yearly ($155.88), and is the plan most teachers and writers need: 300,000 words, plagiarism checks and detection of humanized AI text. Professional costs $45.99 a month, or $24.99 billed yearly ($299.88), and adds 500,000 words, bigger scans and Canvas and Google Classroom integration.
Teams buy Professional seats for each member, schools can ask for a contract, and developers pay separately for the API, from $45 a month for 300,000 words. These are US prices from GPTZero's pricing page in September 2026; GPTZero shows prices in local currency in other countries.
| Plan | Price |
|---|---|
| Free | $0 |
| Premium | $23.99/month, or $12.99/month billed yearly ($155.88/year) |
| Professional | $45.99/month, or $24.99/month billed yearly ($299.88/year) |
| API | From $45/month (300,000 words) |
| Schools and enterprise | Custom |
Full GPTZero pricing breakdown, hidden costs and money-saving tips
How accurate is GPTZero?
What GPTZero says: 99% accuracy on its homepage, a false positive rate (human text wrongly flagged) of no more than 1%, 96.5% accuracy on documents that mix human and AI writing, and a 1.1% false positive rate on TOEFL essays by non-native English writers. These are the company's own figures.
What independent testing found:
| Study | Result for GPTZero |
|---|---|
| Jabarian & Imas, University of Chicago (Oct 2025) | Second tier behind Pangram. Good at avoiding false positives, but false negatives of about 50% or more against humanizer tools across most genres |
| Liang et al., Stanford (2023) | One of seven detectors that together flagged 61% of human-written TOEFL essays as AI on average. This tested GPTZero's early model, before its 2023 switch to a trained classifier |
GPTZero's own help centre says results should not be used to punish students, that accuracy rises with longer text, and that procedural or machine-like human writing can be flagged. For background, read how AI detectors work.
Privacy and data
GPTZero says it keeps a copy of text you check on its website or app and uses it in aggregate to improve the service, but does not share it with third parties and you keep ownership. It says it does not store documents sent through its API. For schools it claims SOC 2 Type II compliance and FERPA, GDPR and CCPA compliance.
Ownership changed in June 2026, when Superhuman, the company behind Grammarly, bought GPTZero and said it would build its tools into the Superhuman Go assistant. If you handle sensitive student data, check the current privacy policy and your school's data agreement before uploading work.
GPTZero vs Turnitin
The two are used side by side in many schools but do different jobs. Turnitin is sold only to institutions, and its AI score is an add-on that students usually cannot see. GPTZero is open to anyone, has a free plan and more public testing, but no archive of past student papers for plagiarism matching. See the full GPTZero vs Turnitin comparison.
- Scan whole documents, not single paragraphs. GPTZero says accuracy is higher at document level than at paragraph or sentence level.
- Look at the confidence category, not just the label. Treat "uncertain" or "moderately confident" results as no firm signal.
- Teachers: ask students to write in Google Docs and use the Writing Report, then talk to the student before acting on any score.
- If you are a non-native English writer or write very formal prose, keep drafts and version history. Formulaic writing is the most common cause of false flags.
- A clean result on text that went through a paraphraser or humanizer means little. Independent testing found GPTZero misses many of those.
GPTZero alternatives
Jargon explained
- False positive
- When a detector wrongly says human writing was produced by AI.
- False negative
- When a detector misses AI-written text and calls it human.
- Humanizer (AI bypasser)
- A tool that rewrites chatbot text so it looks human and slips past detectors.
- Writing replay
- A playback of how a document was typed, edited and pasted, used as evidence of who wrote it.
- Confidence category
- GPTZero's label for how sure it is about a verdict: high, moderate or uncertain.
Frequently asked questions
Is GPTZero accurate?
It is one of the better detectors, but not the best. The October 2025 University of Chicago study put it in the second tier behind Pangram: good at avoiding false accusations, weak against humanizer tools. GPTZero's own 99% accuracy figure is a company claim.
Is GPTZero free?
Yes. The free plan scans 10,000 words a month, up to 10,000 characters per scan, with sentence highlights. Plagiarism checks and bypasser detection need Premium, from $12.99 a month billed yearly. See GPTZero pricing.
Can GPTZero be wrong about human writing?
Yes. Every detector produces false positives. GPTZero says it keeps its rate at or under 1%, but formal, formulaic or non-native English writing is more likely to be flagged. Never treat a score as proof on its own.
Who owns GPTZero?
Superhuman, the company that makes Grammarly, announced it had acquired GPTZero in June 2026. GPTZero still runs as its own product.
Does GPTZero store my text?
Text checked on its website is stored and used in aggregate to improve the service, according to GPTZero's help centre. Documents sent through the API are not stored.
Sources
Every fact on this page comes from public information. Vendor figures are labelled as vendor claims.
- GPTZero pricing (GPTZero)
- GPTZero plan data (US, captured 21 September 2026) (Internet Archive)
- GPTZero homepage (GPTZero)
- GPTZero technology and benchmarking (GPTZero)
- GPTZero for educators (GPTZero)
- What are the limitations of GPTZero's AI classifier? (GPTZero Support Center)
- What languages does GPTZero support? (GPTZero Support Center)
- What happens if I go over the number of words limit of my plan? (GPTZero Support Center)
- Are you storing data from API calls? (GPTZero Support Center)
- Can I purchase a license for my school or department? (GPTZero Support Center)
- How can I pause my subscription? (GPTZero Support Center)
- Artificial Writing and Automated Detection (Jabarian & Imas, 2025) (Becker Friedman Institute, University of Chicago)
- GPT detectors are biased against non-native English writers (Liang et al., 2023) (arXiv / Patterns)
- GPTZero: Robust Detection of LLM-Generated Texts (arXiv)
- Superhuman has acquired AI authenticity service GPTZero (Engadget)
- GPTZero (Wikipedia)
- GPTZero: AI Detection & Writing Replay (Chrome Web Store)
- GPTZero reviews (Trustpilot)
- Pangram pricing (Pangram Labs)
- Originality.ai pricing (Originality.ai)
- QuillBot AI Detector (QuillBot)
- QuillBot Premium (QuillBot)
- Grammarly AI Detector (Superhuman (Grammarly))
- Copyleaks pricing (Copyleaks)
- Turnitin's AI writing detection capabilities FAQs (Turnitin Guides)