FREE AI DETECTOR
A free AI detector and AI checker in one. Paste your text or upload a document and see, sentence by sentence, where it reads like ChatGPT, Claude, Gemini or Llama. No signup, nothing stored.
Click to upload or drag and drop document
Supports PDF, DOCX, and TXT files up to 25MB
Scanning Text with GBT Zero Engine
Tokenizing sentence structures and vocabulary density...
Analysis completed. Flagged passages exhibit low perplexity and predictable syntax patterns typical of automated language models.
Hover or tap on highlighted sentences to see specific diagnostic reasons.
Roughly 8,000 words in one pass
Each with its own baseline
Scored on native baselines
Combined into one score
Discarded after analysis
No detector is infallible, and a score is never proof of authorship. Read what AI detection can and cannot tell you before acting on a result.
LESS GUESSWORK. MORE CONTEXT.
Bring your words. Get the context you need to review them with care.
Try your first scan ↗Paste a passage or upload a PDF, DOCX, DOC, or TXT document. There is room for up to 50,000 characters.
Review AI patterns, natural variation, and mixed signals in one detailed report.
Read highlighted passages in context. Use the findings to guide your review, with your judgment at the center.
Every model leaves a different statistical fingerprint. As an AI checker, GBT Zero keeps a separate baseline per family, so a Claude draft is not scored with a ChatGPT ruler.
OpenAI
GPT-5.6 Sol, Terra, Luna, GPT-5.5, GPT-5
Primary signal: Uniform paragraph length, heavy transitional phrasing, low lexical surprise.
Anthropic
Fable 5.1, Opus 5, Sonnet 5, Haiku 4.5
Primary signal: Hedged qualifiers, balanced clause pairs, consistent register across sections.
Gemini 3.8 Flash, 3.7 Flash, 3.6 Flash
Primary signal: List-forward structure, repeated framing verbs, tightly clustered sentence lengths.
Meta
Llama 3.3, 3.2, 3.1 & legacy Llama 3.x
Primary signal: Template-like openings, repeated syntactical cadences, predictable n-gram continuations.
Jasper AI
Jasper Chat, Boss Mode & Campaigns
Primary signal: Formulaic marketing cadence, repetitive persuasive hooks, high transition density.
DeepSeek AI
DeepSeek V4, V3, R1
Primary signal: Long reasoning chains with unusually even token probability.
Mistral AI
Mistral Large 3, Medium 3.5
Primary signal: Compact declaratives with narrow vocabulary variation.
Microsoft
Microsoft Copilot, Copilot in Office
Primary signal: Summarised source phrasing and formulaic citation lead-ins.
xAI
Grok 4.6, 4.3
Primary signal: Conversational veneer over statistically flat sentence rhythm.
Perplexity baselines are trained per language, because a sentence that looks statistically flat in English can be perfectly natural in German or Japanese. Scanning non-English text with an English-only detector is the single most common source of false positives.
See how GBT Zero AI content detector stands out for articles, blog posts, reports, and other types of content:
Analyze your text for AI documents with sentence-level feedback. See exactly which phrases feel artificial or overly formal so you can refine your writing style and improve the flow of the text.
Detect ChatGPT, Claude, Gemini, and other AI models. Our AI checker identifies machine-like phrasing and inconsistent tone throughout your document.
Get instant, clear feedback alongside AI evaluation. See your AI score and a detailed report explaining why sections sound awkward or overly formal.
Your text stays completely secure with privacy guaranteed. Upload files safely knowing your content is always protected and never used to train language models.
Review sections that feel inconsistent or mechanically phrased. Get guidance to adjust tone for more natural, readable phrasing throughout your work.
Upload documents directly in any format: PDF, DOCX, TXT, and more. No need to copy and paste text multiple times. Process full documents with multi-format compatibility.
An AI detector is a classifier that estimates the probability that a passage was produced by a large language model rather than a person.
It does not look for copied phrases the way a plagiarism checker does. It measures statistical properties of the writing itself, mainly word predictability and sentence rhythm, and compares them against baselines built from known human and known machine text.
The output is a probability, not a verdict. A high score means the text carries strong markers of generation. That is evidence to investigate, not proof of authorship.
How surprising the next word is
Perplexity measures how predictable each word is given the words before it. Language models are trained to pick high-probability words, so machine text tends to sit in a narrow, low-perplexity band. Human writers reach for the odd unexpected word far more often.
Lower perplexity, higher AI probability
How much sentence length varies
Human prose is bursty: a nine word sentence lands next to a thirty word one. Generated prose regresses toward the mean, producing paragraphs where almost every sentence is the same length. GBT Zero scores the variance, not just the average.
Flat variance, higher AI probability
How repetitive the shape of the writing is
Models fall into habits: identical paragraph openings, matched clause pairs, the same connective every third sentence. We fingerprint syntactic patterns across the whole document rather than judging sentences in isolation.
Repeating templates, higher AI probability
Whether the argument actually goes anywhere
Generated passages often restate the premise in new words instead of advancing it. We track how far the meaning travels between sentences to catch fluent text that is informationally flat.
Low drift with high fluency, higher AI probability
The passage is split into sentences and sub-word tokens.
Each token gets a predictability score against per-model baselines.
Sentence scores roll up into perplexity, burstiness and uniformity readings.
Every sentence is colour-coded so you can see which lines drove the result.
YOUR VOICE COMES FIRST
More than a detection score. A starting point for better writing and more thoughtful conversations.
Spot mechanical phrasing before your draft reaches an editor. Review the patterns while preserving your own voice.
Give reports, proposals, and everyday communications a closer review for consistency, clarity, and natural tone.
Find passages that need a closer look across submissions and client drafts. Bring context and human judgment to every review.
Compare raw machine output with authentic human text to see how our detection algorithms analyze tone and predictability.
Artificial intelligence serves as a transformative catalyst across multifaceted sectors. Furthermore, it is imperative to leverage these cutting-edge methodologies to maximize efficiency, streamline organizational workflows, and optimize data processing capabilities.
New software tools help teams finish routine research in minutes. But when projects grow complex, clear thinking and simple communication still make the biggest difference for everyday teams.
No detector is a lie detector for authorship. Knowing where the boundary sits is what separates a useful signal from a bad accusation.
Every detector produces false positives. What matters is what happens next. This is the order to work through, whether you are the writer being questioned or the person doing the questioning.
Under roughly 150 words, no detector has enough variance to measure and scores swing wildly. Rescan the longest continuous version you have. If the whole document is short, the result should not be used at all.
Running Spanish or Hindi prose against an English baseline is the single largest source of false positives industry-wide. GBT Zero keeps per-language baselines, so pick the right one rather than translating first.
Open the flagged lines. If they are definitions, standard disclaimers, method sections or technical boilerplate, that is expected: formulaic writing is genuinely low-perplexity whoever wrote it. A score driven entirely by boilerplate is not evidence of anything.
Version history in Google Docs or Word, dated drafts, notes, browser history, or a commit log all demonstrate authorship far better than a counter-scan. Ask whoever raised the flag to look at your process, because that is the evidence a score cannot provide.
Ask the writer to talk through their argument and their sources. Someone who wrote a piece can explain why they cut a section. Treating a probability as a finding is how institutions end up apologising.
Reported false positives are how baselines improve. Send the passage and the score you saw, and it feeds directly into the next calibration pass.
Reporting a wrong result takes a minute and genuinely helps. Send us the passage.
Every term that turns up in a detection report, defined without the jargon.
Accuracy, privacy, pricing and the limits of detection. If your question is not here, ask us directly.
GBT Zero is a specialized AI detector built to identify machine-generated text patterns. It evaluates vocabulary perplexity, burstiness, and sentence structure variance across models like ChatGPT, Claude, Gemini, and open-weight LLMs. Instead of giving only a basic score, GBT Zero provides sentence-by-sentence diagnostic reports.
A fresh perspective on your writing is one scan away.
