GPTZero Checker
GPTZero is free and open, so if a GPTZero score is what you need, go and get one — you do not have to come through anybody to reach it. What this page is for is the part that comes after: what the score is actually measuring, why sentence-level highlighting tells you more than a document percentage, what its accuracy claim rests on, and the kinds of human writing it reliably gets wrong. Our own sentence-level check is below if you want a second read.
What GPTZero does that most AI checkers do not.
The underlying measurement is shared across the category. These are the parts that are actually particular to this tool.
- It highlights sentences, not just documentsThe thing GPTZero does better than most of the category, and the reason it reached teachers first. Instead of one percentage for a file, it colour-codes which sentences drove the result. That is the difference between being told a document is sixty per cent AI and being shown the four paragraphs responsible, which is the only version a person can actually act on.
- It is built around mixed documentsMost real submissions are not wholly generated or wholly written. They are a draft somebody wrote with two paragraphs pasted in, or a generated outline filled in by hand. Sentence-level scoring is what makes that visible, and a single document score is what hides it.
- The free tier is genuinely usableYou can paste text at gptzero.me without paying and without an account for a reasonable length. Worth saying plainly, because a large number of pages ranking for this term exist to stand between you and a tool you could have used directly.
- It is more candid than the category normGPTZero publishes a 99% figure like everyone else, and it also states in its own materials that no detector is completely accurate and that results should not be used to punish or as a final verdict. That second half is rarer than it should be, and it is the part worth quoting to anyone treating a score as proof.
What GPTZero’s accuracy claim actually rests on.
GPTZero publishes 99% accuracy across diverse datasets and says the figure has been independently reviewed. Before treating that as settled, it is worth knowing something about how this whole field publishes numbers.
Almost every comparison is published by a competitor. GPTZero hosts a comparison of GPTZero against Copyleaks and Originality.ai. Originality.ai hosts a review of Copyleaks. Each finds in a direction you could have predicted from the domain name. That does not make any of them dishonest, and it does mean that reading one without noting who published it is reading marketing as research.
Accuracy is two numbers, and only one gets advertised. Catching generated text and not flagging human text are different problems with different failure costs. A tool can catch nearly everything by being aggressive, at the price of flagging honest work. The false-positive rate is the number that matters to anyone being checked, and it is the one that appears least often in a headline.
GPTZero says the quiet part itself. Its own materials state that no AI detector is completely accurate, that AI is changing constantly, and that results should not be used to punish or treated as a final verdict. If you are ever on the receiving end of a score, that sentence is the most useful thing on this page, because it comes from the people who built the tool.
How ChatGPT, Gemini, DeepSeek, Grok, LLaMA and Perplexity text reads to GPTZero.
The measurement does not change with the model. How confidently it lands, and how patchy the highlighting comes back, changes a great deal.
ChatGPT GPTZero checker
The pairing this tool was built for, and the one it handles most confidently.
GPTZero was founded in response to ChatGPT specifically, and ChatGPT prose is the most heavily represented in every detector's training data. That makes it the case where sentence-level highlighting is most reliable: the passages it colours are usually the ones a reader would have picked out too.
What tends to light up is structural rather than lexical. The opening that restates the question, the evenly weighted middle paragraphs, the closing that summarises what was just said. Newer GPT versions write with more variation, and the practical effect is fewer sentences flagged rather than a different shape being flagged.
Gemini GPTZero checker
Gemini output interacts with sentence-level scoring in a way worth understanding before reading a result.
Gemini structures heavily, returning headings and bullets where continuous prose was asked for. Short fragmented list items give a statistical measurement very little to work with, so a heavily bulleted document produces a patchier, less confident read than the same content written out as paragraphs.
That is not a way of getting a lower score. It means the score covers less of what you submitted, and a fragmented document with a low number is telling you considerably less than continuous prose with the same number.
DeepSeek GPTZero checker
DeepSeek leaves the clearest evidence of any assistant, and no detector is required to find it.
Reasoning-model output frequently still carries the reasoning: a preamble that plans the answer, or an opening paragraph discussing how the question ought to be approached. If a document contains a passage that thinks out loud about how to write itself, the question is settled before any tool is opened.
Its prose also runs technical whatever the prompt asked for, and technical registers are regular by convention. Expect DeepSeek drafts to highlight heavily, and expect genuinely human technical writing to highlight for the same reason.
Grok GPTZero checker
Grok is the least predictable input, and sentence-level scoring shows why particularly clearly.
Its register is more informal and more varied than the other assistants, which raises the surprise of individual word choices and pulls individual sentences down. What you often get is a patchy result: passages flagged hard, passages not flagged at all, and no clean overall verdict.
That patchiness is itself informative. Consistent human writing tends to score consistently. A document that swings between confident flags and confident clears usually has more than one origin, whether that is Grok and a person or two different sittings.
LLaMA GPTZero checker
The hardest case for any detector, because LLaMA is not one thing.
It is weights rather than a product, so what reaches you depends on the application serving it, the system prompt in front of it, and how heavily it was quantised. Two products running the same model name produce differently shaped prose, and a detector calibrated on one generalises poorly to another.
In practice a LLaMA document scores less predictably than a ChatGPT one, and that unpredictability is not a sign of anything about the writer. It is a limitation of measuring output from a model whose deployment you cannot see.
Perplexity GPTZero checker
Worth separating two things that share a word, because the overlap causes genuine confusion here.
Perplexity the product writes to be cited, so its output is hedged toward sources and built to accommodate brackets. Strip the citations before pasting, as most people do, and what remains are sentences leaning on an authority that is no longer named — regular in construction, and that regularity is what gets flagged.
Perplexity the metric is the statistical measure GPTZero and every other detector is built on: how surprising each word is given the ones before it. The company took its name from the metric. Checking text from the product and understanding what the score means are separate topics.
The human writing GPTZero reliably gets wrong.
These are not edge cases. They are large, identifiable groups of people whose ordinary writing scores high for a reason that has nothing to do with how it was produced.
Non-native English speakers. The best-documented failure in the entire category. Competent second-language English tends to be more textbook-regular than a native speaker’s, uses a narrower vocabulary, and follows taught structures more closely. Every one of those raises the score, and none of them is evidence of anything.
Technical and legal writing. Both are uniform by professional convention. A well-written specification is supposed to be predictable, because ambiguity in a specification is a defect. The measurement cannot distinguish disciplined prose from generated prose, because at the level it operates on, they look the same.
Anything written to a template. Taught essay structures, standard report formats, the five-paragraph shape drilled into school students. Following the structure you were taught is the thing most likely to get you flagged for not having written it yourself, which is a genuinely perverse outcome and worth naming.
This is exactly where sentence-level highlighting earns its place. A single percentage on a document like that is unusable. Seeing which four sentences triggered it lets you check whether those are the formulaic passages of something you genuinely wrote, which is a question a person can answer and a number cannot.
GPTZero checker questions.
Can I use GPTZero for free?
Yes. Go to gptzero.me and paste your text; the free tier handles a reasonable length without an account. That is worth stating plainly, because a number of pages ranking for this term exist to stand between you and a tool you could have used directly. We are not GPTZero and we are not going to pretend a detour through us is necessary.
How does GPTZero detect AI writing?
By measuring how predictable the text is: how closely each word follows from the ones before it, and how much sentence length varies across the passage. Generated text scores as more predictable because producing the likeliest next word is what a language model does. GPTZero's distinguishing feature is reporting that sentence by sentence with colour-coded highlights rather than as one document percentage.
How accurate is GPTZero?
It publishes 99% accuracy across diverse datasets and says that figure has been independently reviewed. It is worth knowing that most comparative studies in this field are published by one of the tools being compared, including GPTZero's own comparison against Copyleaks and Originality.ai. Read any of those numbers with the publisher in mind. GPTZero also states directly that no detector is completely accurate and that results should not be used to punish or as a final verdict, which is more candid than the category norm.
Is this page GPTZero?
No, and there is no affiliation. Several sites ranking for this term use the GPTZero name in their domain and imply they are running its model; none of them are. What you can run here is our own sentence-level AI check, which marks the exact phrases that read as AI-written and names why, rather than returning a statistical score.
Can GPTZero be wrong about human writing?
Yes, and it says so itself. Anything naturally uniform scores high: technical documentation, legal text, writing to a taught template, and a great deal of competent English by non-native speakers. Sentence-level highlighting helps here, because it lets you see whether the flagged passages are the formulaic parts of a genuinely human document rather than accepting a single number.
Does GPTZero detect ChatGPT, Claude, Gemini, DeepSeek and Grok?
It reads all of them, since the measurement does not depend on which model produced the words. Confidence varies: ChatGPT output is the most recognisable because it is the most represented in training, Grok scores patchily because its register is more varied, and LLaMA is least predictable because the same model name covers many different deployments.
Do hidden characters or em dashes affect a GPTZero score?
No. Detectors read the words and their predictability. They do not count punctuation, read file metadata, or look for zero-width characters. Cleaning those is worth doing for other reasons and none of it moves a score.
My essay was flagged by GPTZero and I wrote it. What should I do?
Point at GPTZero's own position first: it states that results should not be used to punish or as a final verdict. Then show the process rather than arguing the number — version history, dated drafts, notes, the browser history where you found your sources. Documents that were written leave a trail and documents that were generated do not, and that trail is far more persuasive than a counter-analysis.
What can I check on this page?
Our own AI check, which marks the exact phrases that read as AI-written and names why each was flagged. It is not a GPTZero score, and if a GPTZero score is specifically what you need, their free tier will give you one directly.
Is my text stored?
The document is attached to your account so you can return to it, and you can delete it whenever you like. It is not used to train anything.