Grammarly AI Detector: How It Works & How Accurate It Is
Understand what the Grammarly AI detector measures, how reliable its score is, and check any text for free below — Humanit shows you exactly what reads as AI and lets you fix it.
The Grammarly AI detector estimates how likely a text is AI-generated by measuring perplexity and burstiness — the statistical patterns language models leave behind. It is an estimate, not proof: it can flag genuine human writing and miss edited AI text, so treat any single score as a signal, not a verdict.
How it works
- 1Paste your text. Drop in the writing you want to check against Grammarly-style detection.
- 2Run the free detector. Humanit returns a 0–100 AI-likelihood score, a verdict, and the signals behind it.
- 3See what reads as AI. The subscores show which patterns — predictable phrasing, uniform rhythm, stock vocabulary — are pulling the score up.
- 4Fix it if needed. If it reads as AI, send it to the humanizer to rewrite those signals, then re-check.
How the Grammarly AI detector works
Grammarly’s AI detector estimates the percentage of a document that appears AI-generated and sits alongside its grammar and plagiarism checks. It scores the same predictability and low-variance signals other detectors use, returning a single percentage rather than a full sentence map.
How accurate is Grammarly?
No AI detector is 100% accurate, and Grammarly is no exception. Detection is probabilistic: it estimates likelihood from statistical signals, so it produces both false positives (human writing flagged as AI) and false negatives (edited AI passing as human). Non-native English writing and tightly-structured academic prose are flagged more often. Use the score to decide where to look closer — never as definitive proof on its own.
Who uses Grammarly
Grammarly is most common with students and professionals already writing in Grammarly. If your work is going to be checked by it, the smart move is to check your own draft first with a free detector so there are no surprises — and to rewrite anything that reads as machine-generated before you submit.
Check your text free with Humanit
Humanit's detector scores text 0–100 on the same signals Grammarly uses — perplexity, burstiness, AI vocabulary, and structure — and breaks the result into subscores so you can see *why* a passage reads as AI. Unlike most detectors, it's paired with a humanizer: if your text is flagged, you can rewrite it and re-check in the same place, free every day.
What to do if your writing is flagged
First, don't panic — a flag is an estimate. If the text is your own, you can often clear it by varying sentence length, cutting stock transitions ("moreover", "in conclusion"), and adding concrete, specific detail. If it's AI-assisted, run it through Humanit's Ultra humanizer to restructure the phrasing, then verify with the detector. Always follow your school or employer's rules on AI use.
| Feature | Grammarly | Humanit detector |
|---|---|---|
| Free to check | Limited | Yes — every day |
| Score type | Percentage estimate | 0–100 score + verdict + subscores |
| Flags the AI-tell phrases | Varies | Yes — shows what reads as machine-written |
| Built-in humanizer to fix flags | No | Yes — rewrite and re-check in one place |
| Works on ChatGPT, Claude, Gemini | Yes | Yes |
Frequently asked questions
Is the Grammarly AI detector accurate?
It's reasonably good at spotting raw, unedited AI text, but it is not perfect. Because detection is probabilistic it returns false positives and false negatives, so a Grammarly score should be treated as a signal to review, not as proof.
Can Grammarly detect ChatGPT, Claude, or Gemini?
Yes — Grammarly is built to flag text from all major models by scoring the statistical patterns they share. Heavily edited or humanized text is harder for it to flag.
Does Grammarly flag human writing as AI?
It can. False positives are a known limitation of every AI detector, and clean, formulaic, or non-native human writing is the most likely to be flagged in error. Check your draft yourself before it's scored.
Is there a free Grammarly alternative?
Yes — Humanit's AI detector is free every day, gives you a 0–100 score with subscores, and is paired with a humanizer so you can fix flagged text and re-check in one place.
Will my text be used to train AI?
No. Your text is sent to the model only to produce your result and is never used to train any AI. No content is stored beyond the request.
Does it keep my original meaning?
Yes. Humanit preserves your facts, numbers, names, and citations while changing the phrasing and structure. It never invents new claims.