Will I get flagged for AI if I use Grammarly?

Why Grammarly Users Are Getting Flagged (And Why It's Not That Simple)

A student insists they only used Grammarly for grammar checks — and their essay comes back with a 100% AI score. It sounds like an anomaly, but it's happening often enough that Turnitin has officially acknowledged the pattern. In the company's community forum, a Turnitin engagement specialist confirmed: "We have received several similar reports of this behaviour and are running some tests" (Turnitin community forum).

The reported cases are striking. Faculty on the same forum describe students claiming "only Grammarly" use on work that scored 64%, 73%, and even 100% AI-generated. One instructor, Paul Rittman, ran his own tests and found that text edited only with standard grammar suggestions scored "0% or very low" — leading him to conclude that high scores likely point to Grammarly's AI features rather than basic correction.

That distinction is the heart of the problem. Grammarly isn't one tool; it's a spectrum:

• Grammar and spelling fixes — testing by Originality.ai found "minimal" impact on AI detection scores
• Rephrase and Rewrite suggestions — the same testing found these "can lead to content getting flagged as AI-generated"
• "Use our best version" and GrammarlyGo — full generative rewrites that replace your phrasing with AI output

The tension is obvious: Grammarly is a mainstream writing tool used by millions of students and professionals, yet its higher tiers blur into the same generative AI that detectors are built to catch. As one forum admin put it, free accounts offer suggestions while paid tiers rewrite sentences — "much more of a grey area in terms of acceptability."

There's an uncomfortable wrinkle even for careful users. One analysis reports that grammar correction itself can sometimes raise AI scores, because polishing text makes it more consistent (RewriteAI). Clean, uniform prose is exactly what detectors associate with machine writing — meaning even legitimate editing isn't risk-free.

And the detectors making these judgments are far from infallible. Grammarly's own FAQ concedes that "no AI detector is 100% accurate" and results should "never" be relied on alone (Grammarly). Peer-reviewed research cited by RewriteAI found no detector exceeded 80% accuracy, and documented bias means neurodivergent writers and non-native English speakers get flagged at higher rates.

So the honest answer to "will Grammarly get me flagged?" is: it depends on which features you use, which detector is judging you, and how polished your writing already was. The score is a flag worth investigating — never standalone proof of misconduct. The same caution applies to any AI tooling in your workflow: vetting matters. SkillzBench is building a free directory where agent skills get security-scanned and benchmarked before you rely on them, because trust in AI tools should be earned, not assumed.

Grammar Check vs. AI Rewrite: The Feature That Decides Your Risk

The difference between getting flagged and staying clean comes down to a single choice inside Grammarly: which button you click. Accept a comma fix and you're almost certainly fine. Accept a full sentence rewrite and you've stepped into AI-detection territory.

Two independent lines of evidence converge on the same conclusion. In Originality.ai's controlled test of 10 human-written IELTS essays, text edited only for grammar and spelling showed "minimal" impact on AI detectors — almost all of it still read as human. But essays where the writer accepted every suggestion, including rephrasing, saw a "significant impact" on being flagged as AI-generated.

The faculty evidence matches. On the Turnitin community forum, faculty member Paul Rittman tested texts edited only with Grammarly's standard grammar suggestions and got "0% or very low AI score" every time. He concluded that high scores likely indicate use of Grammarly's AI features — GrammarlyGo — rather than basic correction. Turnitin itself has acknowledged receiving "several similar reports" of Grammarly-correlated flags.

The risk hierarchy looks like this:

• Low risk: grammar and spelling corrections — scored 0% or very low in faculty testing
• High risk: Rephrase, Rewrite, "Use our best version," and GrammarlyGo — flagged at rates up to 100% in reported cases
• Grey area: paid-tier sentence rewrites, which one university admin called "much more of a grey area in terms of acceptability"

Reported forum cases show what "high risk" means in practice: students claiming only-Grammarly use received AI scores of 64%, 73%, and even 100%.

Here's the counterintuitive caveat. RewriteAI's testing found that grammar-corrected content can sometimes score higher for AI detection afterward — because the correction makes prose more consistent. Detectors partly reward messiness, and overly polished, uniform writing is itself a statistical fingerprint. So even careful, grammar-only editing carries a small nonzero risk.

The practical takeaway is simple: use Grammarly as a proofreader, not a co-writer. And if your broader workflow involves AI tools of any kind, vetting what you adopt matters — SkillzBench is building a free directory where every agent skill gets security-scanned and benchmarked before you trust it with your work.

The Uncomfortable Truth: Every AI Detector Is Unreliable

Here's an uncomfortable fact: the US Constitution has been flagged as AI-generated by detectors. If the most famous human-written document in American history can't pass, no score deserves your blind trust.

The detector industry's own players admit this. Grammarly's FAQ states plainly that no AI detector is 100% accurate and that you should never rely on detection results alone. That's an admission against interest from a company selling a detector — and it's the most honest sentence on this topic you'll read anywhere.

The peer-reviewed evidence backs it up. A widely cited 2023 study by Weber-Wulff and colleagues tested 14 detection tools and found none achieved accuracy above 80%. Even Turnitin, the industry giant, claims a false positive rate under 1% while acknowledging the number isn't zero — and a Washington Post analysis of a smaller sample found rates closer to 50%.

The false positives don't fall evenly, either. Research compiled by the University of San Diego Law Library shows detectors disproportionately flag non-native English speakers and neurodivergent writers — precisely the people most likely to use grammar tools like Grammarly in the first place. Ironically, detectors also tend to flag grammatically clean, polished writing, which is exactly what a grammar checker produces.

So what does a high AI score actually mean? Almost nothing on its own:

• Turnitin's own Chief Product Officer says the score is "data for educators to make an informed decision," not a determination of misconduct.
• Detector reviewers note that scores can be manipulated trivially — sometimes just by adding a word like "cheeky" to a prompt.
• Some detectors accepted GPTZero's 50% false positive rate in the Weber-Wulff study as an unavoidable tradeoff.
• Grammarly's detector caught humanized AI content only 6% of the time in one independent review, showing how inconsistent these tools are even with each other.

The practical takeaway: treat any AI score as a prompt to investigate, never proof of anything. If you're flagged, ask for the score, the detector's documented error rate, and present your process evidence — drafts, version history, notes. That documentation matters more than any percentage a detector emits.

The same verification-first mindset applies across AI workflows generally. Whether it's a detector score or an agent skill promising to automate your writing tasks, published research suggests roughly 26% of agent skills carry at least one vulnerability — which is why SkillzBench is building a free directory that security-scans, benchmarks, and version-pins every skill before you trust it. Tools are useful; verified tools are better.

How to Use Grammarly Without Getting Flagged: A Practical Playbook

Knowing where the risk lives is half the battle — the other half is building habits that make an accusation impossible to sustain. The good news: the evidence points to a clear, repeatable playbook.

First, match the tool to the stakes. On work that will pass through an AI detector, stick to Grammarly's grammar and spelling corrections and skip its AI rewriting features — Rephrase, Rewrite, "Use our best version," and GrammarlyGo. Originality.ai's controlled testing found grammar-only edits had "minimal" impact on detector scores, while heavy reliance on AI-suggested rephrasing significantly increased flags, and a Turnitin faculty member independently confirmed that texts edited only with standard grammar suggestions scored "0% or very low AI."

Second, keep your paper trail inside one tool. Draft, edit, and finalize in a single application with intact version history — and save your original drafts. As AdvocatED puts it, a document with no history "is exactly what an accusation looks like." Composing in one app and pasting finished text into another erases the evidence that you, not a model, produced the work.

Third, disclose early. Clarify your institution's or client's guidelines on AI-assisted editing at the start of a project, and state upfront which tools you used. Disclosure handled early is a footnote; disclosure discovered late looks like concealment. Finally, consider Grammarly's Authorship feature, which categorizes text by origin — typed by you, edited, or AI-generated — and lets you control when that report is shared.

If you do get flagged, don't panic, and don't deny that Grammarly contains AI (that argument isn't accurate, since nearly every writing tool now does). Instead:

• Ask for the exact score and the detector's documented error rate. Turnitin claims under 1% false positives, but a Washington Post study found roughly 50% on a smaller sample — and peer-reviewed research (Weber-Wulff et al. 2023) found no tool exceeded 80% accuracy.
• Argue authorship, not tool innocence. Present process evidence: drafts, version history, editing timelines, and an Authorship report showing what you typed.
• Treat the score as a prompt to investigate, not proof. Turnitin's own Chief Product Officer acknowledges the tool "does not make a determination of misconduct" — it provides data for a human decision.
• Remember documented bias: detectors flag non-native English speakers and neurodivergent writers at higher rates, which strengthens a process-evidence defense.

The deeper principle here generalizes beyond writing: when AI touches your workflow, verifiable process beats good intentions. That's the same philosophy behind SkillzBench, which is building a free directory of security-scanned, benchmark-tested agent skills with every version pinned to a commit — so when an AI agent edits, drafts, or automates for you, you can prove exactly what ran and what it did. If automating the rest of your writing workflow appeals, browse and test free agent skills on SkillzBench.

Beyond Editing: Verifying the AI Tools You Rely On

The Grammarly saga teaches a broader lesson: the tools we trust most quietly embed AI, and most users can't tell which button fixes a comma and which button rewrites their voice. AdvocatED's observation cuts to the heart of it — almost every writing tool now contains AI, including the spell-checker built into your word processor. The real risk isn't using AI; it's not knowing what a feature actually does before you click it.

That's why the same "which feature did you use?" question applies far beyond editing. A Turnitin faculty member found grammar-only edits scored 0% or very low on AI detection, while students claiming "only Grammarly" received scores of 64%, 73%, and even 100% when AI rewriting features were involved. The difference between those outcomes was invisible to the users themselves.

Before relying on any AI-powered tool or feature, it's worth asking a few basic questions:

• What does this feature actually do — analyze my text, or generate new text?
• Is the tool's accuracy claim independently verified, or self-reported? Grammarly claims 99% detection accuracy, but one analysis notes no independent figure exists for its detector.
• What are the known failure modes? Turnitin targets a sub-1% false positive rate, yet its own Chief Product Officer acknowledges the risk is not zero.
• Can I document what I did — version history, drafts, disclosures — if my work is ever questioned?

This verification mindset is exactly the problem SkillzBench is building for in the AI agent world. Agent skills — instruction packages that extend tools like Claude Code, Codex, Cursor, and Gemini CLI — are proliferating everywhere, and published research found roughly 26% of them carry at least one vulnerability. Nobody can tell which ones actually help and which are risky.

SkillzBench's approach mirrors the lessons from this article: pin every skill to a specific version, security-scan it, and benchmark it in a sandbox so you can see exactly what it does — and what it changes — before you rely on it. A trust score from 0 to 100, built on security, quality, license, and maintenance signals, replaces guesswork with evidence. Everything is free: the directory, the benchmarks, and the MCP connector that lets you attach only the skills you choose to any agent.

Whether it's a rewriting feature inside Grammarly or a skill running inside your AI agent, the principle holds: know what the tool does, verify it independently, and keep records of your own work. The waitlist for SkillzBench's free directory and MCP connector is open now for anyone who wants verified AI skills from day one.