A student in Pune writes an essay herself, runs it through Grammarly the way she has since school, and gets an email from her professor about an AI score. A marketing manager in Vashi cleans up a proposal with the same tool and a client asks whether a bot wrote it. Both ask the same question: did Grammarly do this?
The honest answer is that "Grammarly" is not one thing. It is a bundle of features that range from fixing a missing comma to drafting an entire paragraph from a prompt, and those sit at very different levels of detection risk. Treating the bundle as a single yes-or-no question is why so much advice on this topic is useless.
Lacewing Technologies is an AI and software development company in Navi Mumbai. We build and operate our own products alongside client work, and one of those products is an AI text detector, so we spend a lot of time looking at what makes a sentence score as machine-written. This post applies that to Grammarly specifically, using Grammarly's own documentation, fetched this week, for every claim about what the tool does.
What do detectors actually measure?#
Not authorship. No detector can see who typed a sentence. What it can see is how statistically regular the sentence is.
Language models write by repeatedly picking a likely next word. The result is text that is smoother and more predictable than most human writing: even sentence lengths, conventional word choices, tidy transitions, very few of the small irregularities a person produces without noticing. Detectors are trained to recognise that smoothness. Grammarly's own AI detector describes the same method, saying it "segments the text and analyzes each section for language patterns that are often linked to AI-generated writing," judging by sentence predictability, repetition and similarity to known AI output.
That framing explains the whole Grammarly problem in one sentence. Any feature that makes your prose smoother, more conventional and more regular moves it toward the statistical profile detectors are looking for, whether or not a model wrote the words. A spelling fix does almost nothing to that profile. A tool that rewrites a sentence to be "clearer" does quite a lot.
Which Grammarly features carry which risk?#
Grammarly's features page groups its help into grammar and spelling, clarity, tone, full-sentence and paragraph rewrites, and generative AI drafting. Those map neatly onto three risk tiers.
Tier 1: spelling, grammar and punctuation. These change a few characters. A corrected "recieve", an added comma, a fixed subject-verb agreement. The sentence structure, word choice and rhythm are still yours. Grammarly describes this group as catching "typos, missing punctuation, grammatical errors, and commonly confused words." On its own, this is unlikely to move a detector in any meaningful way, because the statistical shape of the text is unchanged.
Tier 2: clarity and tone suggestions. Here Grammarly proposes replacing phrases, cutting words, splitting or merging sentences, and swapping tone. Each change is small, but the direction is always the same: toward shorter, more conventional, more uniform sentences. Accept twenty of these across an essay and you have sanded off exactly the irregularity that marks writing as human. Grammarly's own guidance for institutions says these suggestions "do not change the substance of the writing," which is true, but detectors do not read substance. They read surface regularity.
Tier 3: full-sentence rewrites, paragraph rewrites, and generative assistance. This is where model-generated text enters your document. Grammarly's features page advertises the ability to "instantly accept full-paragraph rewrites," and its generative AI support article says the assistant can "compose, rewrite, ideate, and reply," with the option to "prompt our generative AI to change the text in any way you prefer." Text produced this way is model output in the ordinary sense, and a detector will treat it as such. Grammarly's own institutional guidance acknowledges that these features can "meaningfully change writing" and are more likely to raise academic integrity concerns.
The table below puts the tiers side by side.
| Grammarly feature | What it changes | Detection risk | What to do |
|---|---|---|---|
| Spelling, punctuation, capitalisation | A few characters per fix | Minimal | Accept freely |
| Grammar corrections | Word forms, agreement, articles | Minimal | Accept, but read each one |
| Clarity and conciseness suggestions | Phrase swaps, cut words, merged or split sentences | Moderate, rises with volume | Apply selectively; keep sentences that sound like you |
| Tone adjustments | Word choice and register across sentences | Moderate | Use for feedback, write the fix yourself |
| Full-sentence and paragraph rewrites | Replaces your sentence with a model-generated one | High | Avoid in assessed or disclosed work |
| Generative AI (compose, rewrite, reply, ideate) | Produces new text from a prompt | High | Treat as using an AI writing tool; disclose where required |
| AI humanizer | Rewrites the whole passage | High | Not a fix for a flag; Grammarly itself says it is not meant to bypass detectors |
The pattern is simple: the more of your sentence Grammarly writes, the more your sentence looks like Grammarly wrote it.
Why does a "clarity" rewrite look like AI?#
This is the part people find counterintuitive, so it is worth slowing down.
Imagine a paragraph you wrote at 11 pm. One sentence runs to thirty words with a clause tacked on at the end. The next is six words. You used "basically" once because you talk that way. One verb is slightly odd but exactly what you meant.
Now a clarity tool works through it. The long sentence is split in two. "Basically" is deleted. The odd verb becomes the expected one. The short sentence gets a connecting phrase. Every edit is defensible. The paragraph is more readable.
It is also more predictable. Sentence lengths have converged. The vocabulary has moved toward the most probable choice at each position. The transitions are the ones a model would pick, because the tool making the suggestion is itself a model trained on what good, conventional prose looks like. You did not use a chatbot, but you let a model vote on every sentence, and the detector is scoring the votes.
Westcliff University's writing centre says this plainly in its Grammarly guidelines, warning students that applying Grammarly suggestions "can raise the AI percentage in Turnitin" and that "accepting all Grammarly suggestions without review" creates "machine-like prose with AI hallmarks." Their line between acceptable and unacceptable is the student's control: "Students remain in control, evaluating whether a change preserves their meaning."
A single Tier 2 edit will not get you flagged. But they are not free, and the cost compounds with volume.
What does Grammarly itself say about AI detection?#
Grammarly now sells on both sides of this. It offers generative features that produce text, and it offers two tools for showing how text was produced.
The Grammarly AI Detector is a free scanner that returns a percentage of text that "appears to be AI-generated," with sections marked as resembling AI text or showing no AI patterns. What stands out on the page is the volume of caveats. Grammarly writes that "no AI detector is 100% accurate," that "even human-written text can be flagged as AI-generated," that "there is no AI detector that can conclusively or definitively determine whether AI was used to produce text," and that "AI detection should never be used as a standalone verification method." The same page also carries a headline accuracy claim. We would treat that as a marketing figure and the caveats as the operative guidance, which is roughly how Grammarly's own text reads.
Grammarly Authorship is the more interesting tool, because it does not guess. It is an opt-in recorder that, per Grammarly, "records your actual writing process—typed, pasted, AI-assisted" in Google Docs, Microsoft Word or Grammarly's own editor, and produces a report that "color-codes your entire assignment to show each sentence's source," plus a replay of the writing session. Grammarly's support article explains that it distinguishes text "typed directly into your document," text "pasted from a browser-based source," text "pasted from an unknown source," and text "typed and then edited using traditional, non-generative features," with AI-generated text and Grammarly's own "on-demand AI rephrasing" tracked separately.
Two practical details from the same article. Authorship in Google Docs or Word "only works if you provide access to your clipboard," otherwise pasted text falls into the unknown-source bucket. And while basic tracking is in the free plan, "Pro, Premium, and Plus users also have access to AI and plagiarism detection within Authorship reports."
Grammarly is explicit that the report is yours. It "doesn't auto-send it to your professor or anyone else." That makes it less a surveillance tool than a receipt you can choose to produce, and for a student who writes honestly and uses Tier 1 and Tier 2 features, it is the strongest evidence available. Note that it records Grammarly's own generative edits as AI-assisted, which is to say the receipt is honest about Tier 3 too.
Grammarly's AI humanizer deserves a mention because people reach for it after a flag. Grammarly's page states: "This tool is not intended to bypass AI detectors," and adds that using a humanizer "to disguise the use of AI may be considered unethical and could constitute cheating or plagiarism." We agree, and would add the technical point: a humanizer is a rewriting tool, so it belongs in Tier 3 regardless of what it is called.
What do universities say about Grammarly?#
Policies vary by institution and often by course, so nothing here replaces your own handbook. Two patterns are visible in the guidance we could verify.
The feature-level distinction is becoming standard. Westcliff's writing centre lists spelling, grammar, selectively applied clarity edits and tone feedback as acceptable, and lists GrammarlyGO, "Rewrite/Generate" features and paraphrase tools that "replace large chunks of text" as unacceptable, summarising it as "Use Grammarly as a coach, not a ghostwriter." The University of New England in Australia tells students to disable the GenAI component and to assume generative tools are not permitted "unless your UC has explicitly advised otherwise," while noting that "spelling and grammar checking can still be used." Grammarly's own guidance for institutions says students "are ultimately looking to schools to communicate when using generative AI features is appropriate," and that schools with education licences can switch generative features off.
Detector scores are officially a prompt for a conversation, not a verdict. Turnitin's chief product officer wrote that "in cases where we detect less than 20% of AI writing in a document, there is a higher incidence of false positives," that the asterisk on low scores exists "to call attention to the fact that the score is less reliable," and that educators should "use the AI score to start a meaningful and impactful dialogue with their students." When a Liberty University student's video about a Turnitin flag went viral, a Turnitin representative told The Daily Dot that "any positive AI score should only be used as an indication for the educator to investigate further," and pointed to revision history as something students can share.
For an Indian student at a university that licenses Turnitin, or at one of the growing number using its own detector, the implication is the same: the score opens a question, and the answer is your process. Which brings us to what to do.
What should students and professionals actually do?#
Five habits, in order of how much trouble they save.
Accept Tier 1 fixes without worry. Spelling, punctuation, grammar. This is the help Grammarly was built around, it is what most institutions explicitly allow, and it does not meaningfully change your statistical fingerprint. Not using a spellchecker to look more human is a bad trade.
Treat Tier 2 as advice, not autocomplete. Read each clarity or tone suggestion and ask whether the result still sounds like you. If a suggestion flattens a sentence you wrote deliberately, decline it. Westcliff's standard is the right one: you remain in control of every change. If you find yourself clicking accept on everything, stop; that habit is what produces a flagged essay.
Write your own sentences. If a paragraph is weak, rewrite it yourself rather than clicking a rewrite button. The result will be rougher and that roughness is precisely what a detector reads as human. It is also what your professor or client is paying for. If you do use generative features, you are using an AI writing tool, and where disclosure is required you must disclose it. There is no reading of any policy we found where "but it was Grammarly" is a defence.
Turn on Authorship, or keep version history. If your institution accepts Authorship reports, enable it before you start and grant clipboard access so pastes are attributed correctly. If not, Google Docs version history and dated drafts do a similar job. Process evidence is the one thing a detector cannot argue with.
Keep your drafts. Rough notes, an outline, the ugly first version. In every dispute we have seen described, the student or writer who could show how the document came together was fine. The one who had a single final file and a score was not.
For professionals the logic holds. A client who suspects machine-written copy is really asking whether you did the thinking. Drafts, a brief, and a sentence only someone who attended the meeting could have written answer that faster than any score.
How do you check your own text before submitting?#
If detection is part of how you will be judged, scanning your own work first is reasonable. The aim is not to get a green light. It is to see which passages look machine-like and ask why.
Six tools, roughly in the order a student is likely to meet them:
- Turnitin. Sold to institutions, not individuals, so you generally cannot run it yourself. If your university uses it, the guidance above about low scores and conversations is Turnitin's own.
- Grammarly AI Detector. Free, pastes or uploads a file, returns a percentage with sections marked. Useful precisely because it is the vendor of the features you are worried about, and its own page tells you not to rely on the result alone.
- GPTZero. Free scans with sentence-level highlighting, and a Writing Replay feature that, like Authorship, records how a document was typed. Its homepage states that results "should not be used to punish or as the final verdict."
- TextSight. Built by us. It gives an overall AI probability, a humanization score, and highlights individual sentences with their own confidence so you can see exactly which lines drove the result. The free tier allows 1,500 words per scan. It is positioned as a signal for review, not a verdict, and we mean that literally: if it flags a paragraph you wrote, the fix is to add specifics, not to rewrite until the number drops.
- Originality.ai. Aimed mainly at publishers and marketers, with a small free credit allowance. Its own page cautions that "an AI score shouldn't be used alone for academic integrity discipline."
- Copyleaks. Another commercial detector, sold to both individuals and institutions.
Run two of them, not one. Detectors disagree, and a passage flagged by two different methods deserves a second look in a way a single score does not. Then ask what the flagged passage would look like if you had written it in a hurry for a friend. Usually the answer is a concrete detail, a shorter sentence, or a word you would actually use. Make that change yourself.
What you should not do is paste the flagged passage into a rewriting tool, Grammarly's or anyone else's, and resubmit. That converts a Tier 2 problem into a Tier 3 one, and if your institution requires disclosure, it converts an honest essay into an undisclosed AI-assisted one. Rewriting for rhythm and specificity does tend to lower detection scores, because that is what detectors read as human. It is not a guarantee, and it does not remove any obligation to disclose.
So, is Grammarly flagged as AI?#
The spellchecker is not. The clarity and tone coach can nudge you toward it, in proportion to how much of its advice you take without thinking. The rewrite and generate buttons produce AI text, and detectors will treat it as AI text because that is what it is.
Grammarly, to its credit, documents all of this and gives you a recorder to prove how you wrote. Use the tiers, keep the receipts, and write your own sentences. The score will mostly take care of itself, and when it does not, you will have something better to show.