Direct answer
No. Grammarly's AI detector is not included in the free plan; AI detection is bundled with paid Grammarly plans aimed at teams and institutions, and the free tier gives you grammar, spelling, tone, and clarity suggestions only [1]. Even on paid tiers, the detector returns a probabilistic percentage rather than a verdict, and Grammarly itself tells institutions not to treat its output as standalone proof of misconduct [2]. If your real question is "will this draft be flagged when my professor runs it," the tool that matters is the one your institution actually uses — usually Turnitin's AI writing detection inside your LMS [3].
Does Grammarly's AI detector actually work, and what does the free version include?
Grammarly does ship an AI detector, but availability is the sticking point. Detection is attached to paid Grammarly plans rather than the free tier, so a student on the free plan can proofread a draft end to end without ever seeing an AI-likelihood score [1]. What the free plan does give you is surface-level editing: grammar, spelling, punctuation, conciseness, and tone suggestions. Those improve readability, but they do not tell you how an external detector will classify the text.
Where the feature is available, it works by segmenting your document and estimating, for each segment, how likely that text is to have been machine-generated, then rolling those estimates into an overall percentage with highlighted passages [2]. That design is genuinely useful for spotting which paragraphs read as generic — often the ones you drafted fastest or let a model expand. It is not a forensic test, and Grammarly's own guidance frames the output as a signal that should prompt a conversation, not a conclusion [2].
The practical limitation is calibration. Detectors are trained on distributions of human and machine text, so they respond to style as much as to origin: formulaic academic phrasing, heavy templating, and non-native English writing can all push a score upward [2]. A high number from Grammarly therefore does not establish that a student used AI, and a low number does not clear them at their university. Two detectors looking at the same paragraph can disagree substantially, which is exactly why institutions standardise on one system.
How accurate are free AI detectors compared with Turnitin's AI writing detection?
Accuracy comparisons are harder to pin down than marketing suggests, because each vendor validates on its own corpus and reports its own error rates. The more useful question is what the report actually contains and how your institution reads it. Turnitin's AI writing report returns an overall AI score plus sentence-level highlighting, so a reviewer can see which specific sentences triggered the signal rather than a single opaque number [3]. That granularity is what most misconduct processes actually rely on.
Turnitin also builds confidence thresholds directly into the display. When the detected AI share sits below its confidence threshold, the report shows *% instead of an exact figure, explicitly signalling a low-confidence result rather than a precise accusation [3]. Free standalone detectors rarely expose that distinction, which leads students to over-read a "67% AI" badge from a tool their professor has never heard of. Turnitin's own documentation is candid that heavily edited, formulaic, or discipline-specific writing can produce false positives and that reports require contextual human judgement [3].
So the honest comparison is not "which detector is more accurate" but "which detector's output decides your outcome." A free checker that disagrees with your institution's system gives you false comfort or unnecessary panic. If you want to know your actual risk, you need the same detection engine, the same thresholds, and the same report format your markers see [3].
How can students preview the exact Turnitin AI and similarity report before submitting?
The obstacle is structural: in most institutions, students cannot self-submit to the assignment inbox that feeds the institutional paper database, and similarity reports are normally released to students only after an instructor enables them [4]. That means the pre-submission check most students want — the real report, on the real engine, before the deadline — is not available through the university portal. Third-party "free Turnitin" pages that promise it are usually running a different engine entirely.
A legitimate preview needs three properties. First, it must run on Turnitin's actual detection and similarity engines, not a lookalike. Second, it must be non-repository, so your draft is not added to the student paper database and cannot later match against itself or inflate someone else's similarity score [4]. Third, it must return the same artefacts your instructor sees — the similarity report with match overview and source list, plus the AI writing report with its sentence-level flags and threshold display [4].
That is the gap turnitin0.com was built to close. You upload a .docx, .pdf, or .txt file (English, 300–30,000 words, under 20 MB) and receive two PDFs in one checkout: a Turnitin AI detection report and a similarity report, formatted the way they appear in an institutional LMS. Checks are non-repository, turnaround is under 15 minutes in 98% of cases, and there is no subscription — 100,000+ reports delivered to 20,000+ students, with a 4.9/5.0 satisfaction rating. Pricing is pay-per-use: $3.80 for a single check, or $2.75 per check in a 10-check pack.
Knowing that Grammarly's detector sits behind a paid plan — and that even then it is not the engine your university grades against — leaves the same question unanswered: what will your marker's report actually say? turnitin0 runs your draft through Turnitin's own detection and similarity engines and hands back the report itself, so you are deciding on evidence rather than on a percentage from a tool nobody at your institution uses.
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FAQ
Is any AI detector completely free and unlimited?
Free tiers exist across several tools, but they are almost always capped by word count, daily checks, or document length, and none of them run on Turnitin's engine [1]. A free detector can be a useful sanity check on style, not a substitute for the report your institution will generate.
Why does Turnitin show *% instead of a number?
Turnitin replaces the exact AI percentage with *% when the detected share falls below its confidence threshold, indicating a low-confidence signal rather than a confirmed finding [3]. Treat that display as "insufficient evidence," not as a hidden score you need to chase.
Can a high AI score alone get me accused of misconduct?
Detection output is designed as one input to human judgement, and Turnitin's documentation acknowledges that formulaic or heavily edited writing can trigger false positives [3]. Institutions that follow sound practice review the flagged sentences against drafts, version history, and citation records before drawing conclusions.
Does checking my draft with a third-party service add it to Turnitin's database?
Not with a non-repository check. turnitin0 checks your file without adding it to Turnitin's student paper database and does not share reports with third-party databases, so your draft cannot later match against itself [4]. You can also delete files from your account.
Should I humanize my text if a detector flags it?
Only after you understand what was flagged and why. If the flagged passages are genuinely your own writing, revising for specificity and source-grounded detail usually resolves the signal; if a model drafted them, rewriting in your own voice is the substantive fix, not a cosmetic one [2].