AI Detector Guides: How Each One Scores Your Writing
"AI detection" sounds like one test, but it isn't. Every detector measures something slightly different, weights its signals differently, and draws its AI-versus-human line in a different place. A passage that one tool calls human can light up another, and honest human writing gets flagged more often than most people expect. This hub explains how the six most common detectors actually work and links to a focused guide for each, so you can understand a flag instead of guessing at it. If you want to see which sentences in your own draft read as machine-like, run it through our free AI detector.
What every AI detector is really measuring
Almost all current detectors are built on the same underlying idea: large language models produce text that is statistically smoother and more predictable than most human writing. Two terms come up constantly. Perplexity measures how surprising each word is given the words before it — low perplexity means the text takes the "obvious" next word again and again, which is typical of a model optimizing for the most likely token. Burstiness measures variation across sentences: humans mix long, winding sentences with short, blunt ones, while models tend to settle into a uniform rhythm.
Detectors differ in how they turn those signals into a verdict. Some classify the whole document at once; others score sentence by sentence and aggregate. Some were trained mostly on older GPT output and lag behind newer models; others retrain frequently. The practical consequence is that detector scores are estimates of how AI-like a pattern looks, not proof of authorship — which is exactly why false positives on genuine human writing remain a well-documented problem, especially for non-native English writers. For a deeper walkthrough, see how AI detection works.
Turnitin
Turnitin is the detector most students encounter because it's built into the platforms schools use to collect assignments. Its AI writing indicator scores sentences individually, then reports the percentage of the document it believes is AI-generated. Two things make it distinct: instructors usually cannot see the underlying sentence highlights the way you can with consumer tools, and Turnitin itself acknowledges the score is an indicator rather than a determination of misconduct. That gap between a number and a verdict is where most disputes happen.
GPTZero
GPTZero popularized the perplexity-and-burstiness framing and is one of the most widely used standalone checkers. It returns a per-document probability plus a sentence-level highlight view, and it tends to react strongly to text that is uniformly fluent with little structural variation. Because it is free and fast, GPTZero is often the first tool people use to sanity-check a draft. You can compare its behavior against ours with our dedicated GPTZero checker.
ZeroGPT
ZeroGPT is a free, ad-supported checker that returns a blunt "percentage AI" figure and highlights the spans it considers machine-written. It is popular precisely because it has no sign-up wall, but it is also known for being noisy: it can swing hard on short inputs and sometimes flags plainly human text. Treat its number as a rough temperature reading rather than a precise measurement, and never assume a ZeroGPT score predicts what a stricter detector will say.
Originality.ai
Originality.ai is aimed at publishers, agencies, and SEO teams who want to vet freelance and outsourced content at scale. It is generally one of the stricter detectors and pairs its AI score with a plagiarism check, which is why it shows up in editorial and agency workflows. Its strictness cuts both ways: it catches lightly edited AI output that lenient tools miss, but it also produces more false positives on dense, formal human writing.
Copyleaks
Copyleaks markets itself to enterprises and institutions and offers AI detection alongside plagiarism scanning, with support across many languages. It typically returns a confidence level rather than a single hard percentage, and it is frequently integrated into learning management systems and content platforms via its API. Because it is positioned as an institutional tool, a Copyleaks flag often carries more procedural weight than a casual consumer check.
Winston AI
Winston AI targets educators and content teams and reports a "human score," where a higher number means the text reads as more human. It also offers OCR for scanned documents and a readability breakdown, which makes it common in classroom settings. Like the others, its score is a probability estimate, and the same caveats about false positives apply — especially on short, plain, or highly templated writing.
How to use these guides
The approach is the same regardless of detector: start with writing you actually own, check it to see which passages read as flat or mechanical, and revise them so they recover the natural variation in word choice and sentence length your writing usually has. Our rewriting assistant can suggest a more natural version of a passage while keeping your meaning; it is a polishing step, not a substitute for doing the work, and it cannot promise any detector score. Detectors update their models regularly, so no result — clean or flagged — should be treated as permanent or absolute. Always follow your school's or employer's rules on AI use.
If your own honest writing keeps getting mislabeled, the workflow is simple: check it with the AI detector to see which sentences trigger the flag, revise them in your own voice (or with the rewriting assistant), and read the result yourself to make sure it still says what you mean.
Frequently asked questions
Can any tool guarantee a detector score?
No. Writing that varies its word choice and sentence rhythm the way human writing naturally does tends to read as less machine-like, but no tool or method can guarantee what any detector will say — detectors retrain, and each one weights its signals differently. We do not promise detector outcomes, and you should be wary of anyone who does.
Are AI detectors accurate?
They are estimators, not proof. Detectors measure statistical patterns such as perplexity and burstiness and report a probability that text is AI-generated. Independent testing and the detector vendors' own disclaimers acknowledge that false positives occur, particularly on short, formal, or templated human writing. A score should inform a judgment, not replace one.
Why does one detector flag my text while another clears it?
Each tool was trained on different data, classifies at a different level (whole-document versus sentence-by-sentence), and sets its threshold in a different place. A passage that looks borderline to a strict tool like Originality.ai can read as clean to a more lenient one. That is why we publish a separate guide per detector.
What should I do if my own writing is flagged?
Keep your drafts, notes and version history, which are the strongest evidence of authorship. Ask which tool produced the score, and point out that detector vendors describe their scores as indicators, not proof. Passing off generated work as your own where rules forbid it is never acceptable; these guides explain how the tools work so honest writers can understand and contest a false flag.
Will rewriting my text change its meaning?
A good rewrite varies phrasing while preserving your argument and facts, but no rewrite is perfect. Always read the output before you use it to confirm it still says what you intended and hasn't introduced errors, especially in technical or cited passages.
See which sentences read as AI, before you submit
Paste your draft into the free AI detector to see which sentences trigger the patterns detectors look for, and why. No account needed.
Check My Writing