AI Detection

AI detection,
honestly explained.

AI detectors don't read meaning — they measure how statistically predictable your writing is. Here's how that actually works, why genuine human writing gets flagged, and an honest breakdown of every major detector you might face.

How AI detection works

AI detection works by scoring how predictable and how uniform your text is, then comparing that signature against patterns learned from machine-generated writing. Two signals do most of the work: perplexity — how surprised a language model would be by each word — and burstiness — how much your sentence length and rhythm vary. Large language models like ChatGPT, Claude, and Gemini are tuned to produce fluent, likely text, so their output sits at low perplexity and even burstiness. The full mechanics are in how AI detectors actually work.

Why human writing gets flagged

Detectors flag real human writing whenever it happens to look predictable — and a lot of legitimate writing does. Clear, conventional, grammatically clean prose has low perplexity for reasons that have nothing to do with AI, which is why non-native English writers and authors of formulaic or technical text are flagged disproportionately. A score is a signal for a human to weigh, never proof — see how accurate AI detectors really are.

Every major AI detector

Here's an honest breakdown of the detectors you're most likely to encounter — what each one measures, its false-positive record, and where we stand. We don't claim to beat any of them.

  • Compilatio Compilatio is a European academic-integrity tool that pairs plagiarism checking with AI-content detection, widely used by universities and schools across France and the rest of Europe.
  • Content at Scale Content at Scale is an AI-content platform that also offers a free AI detector, popular with marketers and writers who want a quick read on how machine-like a draft looks.
  • Copyleaks Copyleaks is an enterprise and education platform that pairs AI detection with plagiarism checking and integrates into learning-management systems via its API.
  • Crossplag Crossplag is an education-focused tool that pairs plagiarism checking with an AI-content detector, marketed to schools and universities reviewing student submissions.
  • GPTZero GPTZero is one of the most widely used consumer- and education-facing AI detectors, popular with teachers checking student work.
  • Grammarly AI Detector Grammarly, the widely used writing assistant, has added an AI-detection feature that estimates how much of a document may have been generated by AI.
  • Hive Moderation Hive Moderation offers AI-content detection, including an AI-generated text classifier that platforms and businesses use to flag machine-written content at scale.
  • Originality.ai Originality.
  • Packback Packback is an education platform for discussion and writing feedback that many colleges use, and it added AI-writing review to its instructor-facing tools so teachers can flag work that reads as machine-generated.
  • QuillBot AI Detector The QuillBot AI Detector is QuillBot's free tool for estimating whether text was written by AI — a separate feature from the paraphraser QuillBot is best known for.
  • Sapling Sapling is the AI detector we are most transparent about, because it is the same detector we use to score our own output.
  • Scribbr Scribbr is a popular, student-facing AI detector offered as a free quick check, powered by a third-party detection model.
  • Smodin Smodin is a multi-tool writing platform that bundles a paraphraser, summarizer, and an AI-content detector alongside its other features.
  • Turnitin Turnitin added AI-writing detection to its similarity report in 2023; it now also flags text that has been run through paraphrasers and "humanizers.
  • Winston AI Winston AI is a paid AI detector aimed at education and enterprise users, marketed around high claimed accuracy and extras like OCR for scanned documents.
  • Writer.com Writer.
  • ZeroGPT ZeroGPT is a free, widely used consumer AI detector that anyone can paste text into, which is why it shows up so often in quick checks of student and web writing.

Detector vs detector

Different detectors disagree on the same text, so it helps to know how the major ones compare head-to-head — who uses each, and which one you'd actually face.

Go deeper

Where we stand No tool — including Humanizer — can guarantee passing any detector. What Humanizer does is rewrite text to read more naturally and show you a Sapling-based detector score on every result, so you get a clearer picture instead of an empty promise. Compare the field on the best AI humanizer page.

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FAQ

AI detection, answered.

AI detectors estimate how statistically predictable your text is, not whether it is true or original. They measure perplexity (how surprising each word is to a language model) and burstiness (how much sentence length and rhythm vary), then a trained classifier converts that signature into a probability that the text is AI-generated. None of it reads meaning — it only describes the shape of the prose.