Does Grammarly get flagged as AI?
Grammar checking and AI drafting are different things, but detectors cannot tell them apart, because both leave the same fingerprint.
Short answer: using a grammar checker can raise your score, and the reason has nothing to do with the checker being an AI tool. It is about what editing does to prose.
This applies to Grammarly, to Word's editor, to LanguageTool, and to a careful human copy editor. The mechanism is the same for all of them.
Editing smooths, and smoothing is the signal
Detectors do not look for a watermark. They measure how regular text is: how much sentence length varies, how predictable each word is, how evenly the rhythm runs. More on that in how AI detectors work.
Every grammar checker pushes prose in the same direction:
- Shorter, simpler sentences, because it flags long ones as hard to read
- Consistent terminology, because it flags variation as inconsistency
- Removed redundancy, which takes out the digressions and asides
- Conventional constructions, because the unconventional ones get marked as errors
Each of those is a real improvement to clarity. All four also strip out variation, and variation is precisely what a detector reads as human.
Measured across our corpus, human writing has a median within-document sentence-length standard deviation of 8.7 words. Generated text sits at 6.4. Accept enough suggestions and your prose moves along that axis, toward the generated end, without a single word being drafted by a model.
The suggestion features are a different case
Worth separating two things that share a brand.
Grammar and spelling correction changes your words locally. It nudges the score.
Generative features, the ones that rewrite a sentence for tone or produce text from a prompt, are actually generating text. That output has the statistical profile of generated text, because it is generated text.
Most tools now bundle both. If you accepted a rewritten sentence rather than a comma correction, the second case is what happened.
What this means practically
A detection score cannot distinguish between:
- text a model drafted
- text you wrote and a grammar checker tightened
- text you wrote carefully in a formal register
- text you wrote in your second language
All four land in similar territory, because all four are regular. That is the core limitation of the whole method, covered in why AI detectors flag human writing.
It is also why the same care that gets you a better mark can get you a higher AI score. Nobody designed that. It falls out of what is being measured.
If you want to know before you submit
The score exists whether or not you look at it. Seeing it beforehand is strictly more useful than seeing it afterwards, because beforehand you still have options.
Ours is free and unlimited, no account, and it scores each paragraph separately rather than handing you one number. That matters here, because if grammar checking is what raised your score you will usually see it spread evenly across everything rather than concentrated in one section. A single heavily flagged section says something different from a document that is uniformly a bit elevated.
If a passage does come back high and you want to bring the variation back, the changes that work are structural rather than lexical: vary your sentence lengths, cut the connectives at the start of sentences, resolve stacked hedges. Those are in what makes text read as machine written and paragraph rewriting.