Grammarly AI Detector vs Grammarly Authorship
Grammarly ships two features that get confused constantly — an AI detector that guesses from the finished text, and Authorship, which records how the text got into the document. They work completely differently, and only one of them can be affected by editing. Check any text free below.
Grammarly has two separate AI features: a detector that estimates an AI percentage from the writing itself, and Authorship, which logs how text entered the document — typed, pasted, or AI-generated — as you write.
Works with every major AI model
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.
Two different features, constantly confused
Almost every question about "the Grammarly AI detector" is really about one of two separate things. The first is a conventional AI detector: it reads finished text and estimates a percentage of it that looks machine-generated, using the same statistical signals every other detector uses. The second is Authorship, which is not a detector at all. Authorship works inside the Grammarly editor and records how text arrived — typed by hand, pasted from elsewhere, generated by an AI prompt, or edited with Grammarly's own suggestions — then produces a report on the finished document. One guesses backwards from the words. The other watched it happen.
Why that distinction matters more than the score
It changes what is even possible. A statistical detector can be wrong in both directions and can be affected by rewriting, because it only ever sees the final text — that is the whole basis on which humanizers work. Authorship is a provenance record, and rewriting a document afterwards does not change what was logged while it was being written. If your institution asks for an Authorship report, no rewriting tool — this one included — changes what that report says, and any product implying otherwise is selling you something that does not work. We would rather tell you that than take the sale.
How Grammarly's AI detector scores text
The detector itself is unremarkable, which is not an insult — they all work this way. It scores how predictable the word choices are and how uniform the sentence rhythm is, then returns a single overall percentage rather than a full sentence-by-sentence map. Because it sits inside a tool people are already writing in, it is one of the most-encountered detectors in the category simply by placement. Basic checks come with a Grammarly account; the fuller detection and Authorship reporting sit on paid tiers.
Does Grammarly itself make your writing look AI-generated?
This is the anxious question underneath most searches on this topic, and it deserves a straight answer. Accepting a lot of Grammarly suggestions does tend to push writing toward the smooth, conventional, low-variance register that detectors score as machine-like — not because Grammarly wrote it, but because heavy grammar correction and AI generation both flatten the same irregularities out of prose. Grammarly's own Authorship reporting distinguishes "edited with Grammarly" from "generated by AI" for exactly this reason. If you are worried, the fix is not to stop proofreading: it is to leave some of your own rhythm alone, and to keep sentences varied in length even where a suggestion offers to tidy them.
How reliable is any of it?
The detector half carries the same limits as every statistical detector. Independent testing of detectors as a class has repeatedly found meaningful false-positive rates, and a 2023 peer-reviewed study in Patterns found more than 61% of genuine TOEFL essays by non-native English speakers were misclassified as AI. OpenAI withdrew its own AI-text classifier in July 2023 citing low accuracy — by its published numbers it caught 26% of AI text while wrongly flagging 9% of human writing. The Authorship half is a different kind of claim: it is a log of what happened in one editor, which is more dependable about what it covers and covers only text written inside Grammarly.
Check your text free — no account, no limit
The detector at the top of this page is free, unmetered, and needs no sign-up. It returns a 0–100 AI-likelihood score broken into sub-signals — perplexity, burstiness, AI vocabulary, discourse markers, structure, personal voice — and names the exact phrases reading most machine-written, so you know what to change rather than just that something is wrong. If a passage reads as AI, you can hand it straight to the humanizer and re-check the result here. Like Grammarly's score, it is an estimate — treat it as one.
Who it's for
| Feature | Grammarly | Humanit detector |
|---|---|---|
| Free to check | Limited | Yes — every day |
| Score type | Percentage | 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 |
| AI detector | Authorship | |
|---|---|---|
| What it does | Estimates an AI % from the finished text | Records how text entered the document |
| What it sees | Only the words you ended up with | Typing, pasting, AI generation, edits |
| Can it be wrong? | Yes — false positives and negatives | It reports what it logged, in that editor |
| Affected by rewriting after the fact? | Yes | No |
| Covers text written elsewhere? | Yes — any text you paste in | Only writing done inside Grammarly |
Frequently asked questions
Does Grammarly detect AI writing?
Yes, in two different ways. Its AI detector estimates a percentage from the finished text, like any other detector. Separately, Authorship records how text entered the document while you were writing — typed, pasted, or AI-generated — and reports on that. They answer different questions and only the first is a guess.
What is the difference between Grammarly's AI detector and Authorship?
The detector reads the final text and infers. Authorship watched the document being written and logged it. That means rewriting a document can change what a detector says about it, but does not change what an Authorship report recorded.
Can a humanizer beat Grammarly Authorship?
No — and be sceptical of anything that says otherwise. Authorship is a record of how the text was produced, not an analysis of the words, so editing the words afterwards does not alter it. Humanizers work on statistical detectors, which is a different problem.
Does using Grammarly make my writing get flagged as AI?
Grammarly does not write your text, but accepting a lot of corrections smooths out the sentence-length variation and irregular phrasing that detectors read as human. That can nudge a score upward. Keeping some variety in your sentence lengths is the practical countermeasure.
Is Grammarly's AI detector free?
Basic checks come with a Grammarly account, with fuller detection and Authorship reporting on paid tiers. The detector on this page is completely free, unlimited, and needs no account at all.
How accurate is Grammarly's AI detector?
It carries the same limits as every statistical detector — real false-positive rates, and much weaker performance on edited AI text. A 2023 study in Patterns found over 61% of genuine non-native English essays were misclassified by the detectors it tested. Use any single score as a prompt to look closer, not as a conclusion.
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.