Updated August 2026 · Grammarly's own pages re-read August 1
Grammarly AI detector and humanizer: the best AI humanizer for the Grammarly AI checker
Grammarly is the only detector in this category that is already installed on the machine of the person reading your work. It is free, it needs no account, and it sits in the browser, in Google Docs, in Word and in Gmail.
It also ships the one thing a humanizer genuinely cannot beat. Here is the difference, and what each tool costs.
2 free runs a day, up to 200 words each. We save your run so you can get back to it, and a delete button appears with the result. See privacy.
This is our own AI-pattern score, measured here on sentence rhythm, template phrases, vocabulary variety and passive voice. It is not a GPTZero, Turnitin, Originality.ai, Copyleaks or ZeroGPT result, and it does not predict one. Worth knowing: we also ask the rewrite to vary sentence length, drop template phrases and prefer the active voice, so some of the drop is built in. Read the two panels below, not just the number.
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After ·
Meaning kept · Your own text rewritten · Saved to your history, delete any time
The short answer
Grammarly runs two completely different systems and buyers keep confusing them. The AI detector is a statistical guess on finished text, it is free to run with no account, and a genuine rewrite moves it. Authorship is a recording of how the document was produced, typed against pasted against AI-generated, and no humanizer on earth changes it, ours included. So the honest answer is: a humanizer is worth buying for the first one and useless against the second, and the second only exists if Authorship was switched on before you started writing, inside Google Docs or Microsoft Word. For the checker itself, Undetected.ai rewrites in one pass and shows our own AI-pattern score before and after, from $9 a month for 15,000 words. Undetectable.ai is the cheapest serious option at about $5 a month billed yearly. WriteHuman meters by request rather than by word. QuillBot is the closest substitute for Grammarly itself and makes no detector promise at all. Grammarly now ships a humanizer of its own too, and rules out on its own page the job most people buy one for, which we go through on the Grammarly AI humanizer page.
Last updated August 1, 2026. Grammarly's AI detector page and Authorship page were read that day. QuillBot was re-read August 1, Undetectable.ai, WriteHuman and Walter Writes July 31, BypassGPT July 14. All figures in USD, and promotional rates move constantly, so confirm before you buy. We are not affiliated with Grammarly.
Before you buy anything
The three Grammarly products people call "the Grammarly AI detector"
This is the whole decision in one table, and almost nothing else written about Grammarly separates these out. Two of them are guesses about your text and one of them is a record of your keystrokes. A humanizer is worth money against the first two and worth nothing against the third. Every detail below was read off Grammarly's own pages on August 1, 2026.
| What it is | What it actually does | Can a rewrite move it? | What it costs |
|---|---|---|---|
| The free AI detector | A statistical guess made on finished text. You paste a passage in and it returns "X% of this text appears to be AI-generated", with the passages split into "Resembles AI text" and "No AI patterns found" | Yes | Free, and no account is required |
| The AI Detector agent | The same reading delivered inside the Grammarly product, with inline explanations of which passages triggered it and one-click rewrites offered on the spot | Yes | Grammarly Pro |
| Authorship | A recording, not a guess. It labels text as written by you, created with AI, or edited with Grammarly, color codes every sentence in a shareable originality report, and lets a reader replay your writing process from the first paste to the last keystroke | No | Available in Grammarly Free and Grammarly Pro |
The free AI detector
This is the one that most people mean, and it is the one a rewrite changes, because it is reading the text rather than your history.
The AI Detector agent
Same underlying signal, better packaging. The one-click rewrite is Grammarly quietly shipping a humanizer next to its own detector.
Authorship
No humanizer on earth edits this, ours included. It is a log of how the document came to exist, and rewriting the words afterwards does not change the log.
The practical consequence is worth stating plainly, because it decides whether you should spend anything at all. Authorship only stores data for text you paste into Google Docs or Microsoft Word after you switch it on. It cannot be pointed backwards at a document you already finished, and it cannot be switched off retroactively for one it already recorded. If Authorship was never running, the only thing standing between you and a Grammarly reading is the text itself, which is the part a humanizer can genuinely change. If it was running the whole time, no purchase on this page helps you, and we would rather tell you that than sell you something.
Why this detector behaves differently
Grammarly is the checker nobody had to go and buy
Every other detector in this category takes a decision to use. Somebody signs an institutional contract, installs an LMS integration, or pays for a scan. Grammarly took that decision out of the loop, and that changes who runs it on you and why.
| Detector | What it takes to run it on your text | Can you check yourself first? |
|---|---|---|
| Grammarly | Nothing. The web checker is free with no account, and the extension is already sitting in tens of millions of browsers, Google Docs files and Outlook windows | Yes, in about ten seconds, for free |
| Turnitin | An institutional license. Turnitin does not sell to individuals, and its AI writing report goes to the instructor rather than to the writer | No, unless your university enables an LMS self-check, and a minority do |
| Copyleaks | A paid plan or an LMS integration. Personal starts at $13.99 a month billed annually, metered in credits at 250 words each | Only within a limited free credit allowance |
| Originality.ai | A paid account. Pro is $12.95 a month billed annually, with credits that expire monthly, and there is no free scan | No, not without paying |
| GPTZero | Nothing for the basic check. It has a free tier, and its paid pricing is rendered client-side and could not be read | Yes, on the free tier |
| ZeroGPT | Nothing for the free tier, which the site describes as free forever at 100,000 characters per detection. Paid plans start at $12.99 a month | Yes, free |
Read that column on the right and the buying decision reorganizes itself. The detectors that carry the heaviest consequences are the ones you cannot test against, and the one you can test against for free is the one most likely to be run on you casually, by a colleague pasting your email into a box or a hiring manager glancing at a cover letter. That is a good trade for you, and it is the reason we tell people to pre-check with Grammarly before they spend money anywhere: it is the cheapest honest feedback loop in the category. We wrote up the full picture of what you can verify without paying in the AI humanizer that actually works.
The number behind the number
Grammarly claims 99 percent, and a published test returned 37
Grammarly's AI detector page states that it "achieves 99% detection accuracy and ranks #1 on RAID's independent benchmark." RAID is real and it is serious: an academic benchmark built from more than 670,000 texts spanning many writing styles, many generating models, and deliberate attempts to fool the detectors. Placing first on it is a genuine achievement and we are not going to pretend otherwise.
Then there is what happens when somebody pastes something in. PCWorld tested four AI detectors on a short story written entirely by Google Gemini. Grammarly returned 37 percent, and returned 37 percent again on a second run. The result was consistent and badly wrong.
Both things are true, and the gap between them is the most useful thing on this page. A benchmark score measures average behavior across hundreds of thousands of samples drawn from a fixed distribution. Your document is one sample, in your voice, on your subject, at your length, possibly after an edit. Detectors are far more stable in aggregate than they are on any individual passage, which is exactly why a headline accuracy figure tells you almost nothing about the reading you are about to get.
Grammarly, to its credit, says this itself. The same page carries the lines "no AI detector is 100% accurate" and "AI detection should never be used as a standalone verification method." That is a vendor telling you not to over-read its own product, and it is a better guide than anything a humanizer company will tell you, including us.
For context that does not come from any vendor: independent testing of AI detectors on real-world writing lands nearer 85 to 90 percent accuracy, with false positives in the 8 to 15 percent range, and a Stanford study found 61.3 percent of essays written by non-native English speakers were wrongly flagged as AI. If you write in English as a second language, no headline number in this category is describing you. We keep those same figures on every page of this site so nothing here contradicts anything else. If you want the head-to-head, we put Grammarly against the detector with the real institutional consequences in Grammarly AI detector vs Turnitin.
The comparison
Six AI humanizers priced side by side
Entry price is each vendor's cheapest paid plan. Where the yearly rate is cheaper we lead with it and put the monthly figure in brackets, because that is the number buyers actually compare. The free-allowance column is there because Grammarly is free to check against, so you can genuinely test any of these before committing.
| Tool | Entry price | Volume | Free allowance | Best for |
|---|---|---|---|---|
| Undetected.ai | $9/mo yearly ($12 monthly) | 15,000 words/mo on Starter, 80,000 on Pro, 250,000 at $39 | Free account: 3 runs a day, 9,000 words a month | Anyone whose drafts get pasted into a document someone else has Grammarly running on |
| Undetectable.ai | $5/mo yearly ($9.99 monthly, $60/yr) | 10,000 words/mo on the entry tier, 20,000 at $9.50/mo yearly | Yes, a free trial (allowance not stated on its pricing page) | Buyers who want the lowest annual price from the best-known brand |
| WriteHuman | $12/mo yearly ($18 monthly) | 80 requests/mo at up to 600 words each on Basic, unlimited on Ultra | Yes, 3 requests/mo at 250 words | Writers filing a few long documents rather than a steady stream of short ones |
| Walter Writes AI | $8/mo billed yearly ($96/yr) | 30,000 words/mo on Starter with a 750-word cap per request, 70,000 on Pro | Free usage offered, limit not published | High monthly word counts on a small budget, if the per-request cap suits you |
| BypassGPT / HIX Bypass | $8/mo yearly on promo ($12 monthly), read July 14, 2026 | 5,000 words/mo on Basic, 30,000 on Pro | Yes, 150 words/mo | Buyers who want to see output quality before paying anything |
| QuillBot | $8.33/mo yearly ($19.95 monthly), re-read August 1, 2026 | Unlimited paraphrasing on Premium, humanizer capped on free | Yes, 125 words per paraphrase | Writers who want rewriting and grammar help rather than detector clearance |
We build one of these tools, so read our row with that in mind. The rest of the page is where the others beat us.
Undetected.ai
The rewrite rebuilds sentences rather than swapping words, which is what Grammarly's checker actually reads, and our own AI-pattern score shows what changed. It is also why we say plainly on this page that no rewrite touches Authorship, the half of Grammarly nobody selling you a humanizer wants to mention.
Best for: Anyone whose drafts get pasted into a document someone else has Grammarly running on.
From: $9/mo yearly ($12 monthly).
Undetectable.ai
The most established product in the category, with writing-style matching, unlimited detection checks and an API on every tier. Billed yearly it undercuts everything else here, though the entry plan carries 10,000 words a month against our 15,000.
Best for: Buyers who want the lowest annual price from the best-known brand.
From: $5/mo yearly ($9.99 monthly, $60/yr).
WriteHuman
Meters by request instead of by word, which is cheaper if you file a handful of long pieces a month. It also publishes a word-priced REST API and an MCP server, so an agent can call it as a tool inside a writing workflow.
Best for: Writers filing a few long documents rather than a steady stream of short ones.
From: $12/mo yearly ($18 monthly).
Walter Writes AI
The most words per dollar on this page and an interface in 80-plus languages, but the 750-word cap per request on the entry plan splits a 3,000-word document into four passes, and the seams between passes are where tone drifts.
Best for: High monthly word counts on a small budget, if the per-request cap suits you.
From: $8/mo billed yearly ($96/yr).
BypassGPT / HIX Bypass
The most specific detector claims in the category and a genuine free allowance, though 150 words is a taste test rather than a work session. Its pricing page sits behind a Cloudflare check we could not read this month, so treat the price above as a July 14 snapshot.
Best for: Buyers who want to see output quality before paying anything.
From: $8/mo yearly on promo ($12 monthly), read July 14, 2026.
QuillBot
A full writing suite with nine paraphrase modes, a plagiarism checker and citation tools. It is the closest thing here to a direct Grammarly substitute, and it is honest enough not to promise you a detector result.
Best for: Writers who want rewriting and grammar help rather than detector clearance.
From: $8.33/mo yearly ($19.95 monthly), re-read August 1, 2026.
How to choose
Five things that decide whether a humanizer holds up against Grammarly
Price is the easiest thing to compare and the least useful. These are the differences you notice the first time someone reads the rewritten version.
1. Rebuilt sentences, not swapped words
Grammarly's checker reads how predictable each sentence is and how evenly the rhythm runs across a passage. A tool that replaces words with rarer synonyms leaves both of those properties intact, so the reading barely moves while your prose starts sounding like a thesaurus fell on it. Grammarly is free to run, which means you can settle this argument yourself in a minute: paste the original, note the number, paste the rewrite, compare. Do that before you pay anyone, including us.
2. Does it survive contact with Grammarly's other job?
This is the Grammarly-specific trap and nobody warns you about it. Grammarly is primarily a grammar and style engine, and the same passage a humanizer roughed up to look less machine-made is the passage Grammarly will now underline in every color it owns. If your rewrite has to sit inside a document where Grammarly is also correcting you, you want output that reads cleanly, not output that is deliberately awkward. Awkwardness is a cheap way to move a score and an expensive way to look like a writer.
3. Does your meaning survive the pass?
Cheap tools fail hardest here and the damage is quiet. "Fell 40 percent" becomes "fell noticeably" and your evidence is gone. A cited author's name gets swapped for a near-synonym. A quoted passage stops matching its source. Paste in a paragraph with numbers, names and citations, then check every single one survived. A clean detector reading on mangled copy is worth less than no rewrite at all, and it is worse in a document someone is going to read carefully.
4. One pass, or a detector at a time?
Grammarly is almost never the only checker a document meets. A cover letter screened by Grammarly might be scanned again by an applicant tracking system. An essay pre-checked in Google Docs still lands in Turnitin. Detectors weight signals differently, so a rewrite tuned for one can come back flagged by another, and each extra pass you run costs you more meaning. Test any candidate against two or three checkers, not only the one it happens to recommend.
5. Ask whether you need one at all
If Authorship was recording while you wrote, buy nothing. Rewriting the words does not touch the log, and the log is the thing your reader will open. If it was not recording, and Grammarly is reading your finished text cold, then a genuine rewrite is doing real work against a real signal. That is the whole decision, and you can answer it for free in the time it takes to check whether Authorship was ever switched on in the document.
The ten-minute test
Take 400 words of something real you wrote, not a sample paragraph from a demo. Run it through Grammarly's free checker and write the number down. Run it through any tool you are considering, then check it again. Confirm every number, name and citation survived. Read the output aloud and ask whether someone who knows your writing would notice. Grammarly makes this the one detector in the category where that whole loop costs nothing, so use it.
Being straight with you
What no humanizer can do, and where the others beat us
Nothing sold on this page touches Authorship. Not ours, not anyone's. Authorship records whether text was typed, pasted or generated, sentence by sentence, and lets a reader replay the document from the first paste to the last keystroke. That is provenance, not statistics, and a rewriting tool operates on the finished words rather than the history behind them. Anyone who implies otherwise is either confused about which Grammarly product you are asking about or hoping you are.
Nobody can promise you a Grammarly number. The model gets retrained, the same text can read differently across two runs on two products, and Grammarly's own page says AI detection "should never be used as a standalone verification method." What a humanizer can honestly claim is that it changes the statistical properties the classifier measures. Whether that lands you under any particular threshold is not something a vendor gets to guarantee.
The 99 percent claim and the 37 percent result are both real. We are not going to spin either one. Grammarly does top the RAID leaderboard, and PCWorld's hands-on test of fully AI-written text did come back at 37 percent twice. Benchmarks measure averages, individual pastes do not, and a category that quotes only the first number at you is doing you a disservice.
We do have a free account, and it is small on purpose. Three runs a day of up to 1,500 words, 9,000 words a month, no card. Anyone can also run the demo on this page twice a day without an account at all. Paid plans are planned from $9 a month for 15,000 words and are not on sale yet. If your budget is genuinely zero, BypassGPT's 150 free words a month or WriteHuman's three free requests will serve you better than we will, and QuillBot's free paraphraser is more generous than either. We would rather say that than have you buy on a misunderstanding.
On price alone, Undetectable.ai wins. About $5 a month billed annually undercuts everything here, and it is the most established product in the category with a wider feature surface than ours. It carries 10,000 words a month on that tier against our 15,000 at $9, so weigh the two numbers together rather than reading the headline price on its own. We published their full pricing including cost per 1,000 words if you want the arithmetic.
If you want a Grammarly replacement rather than a humanizer, look at QuillBot. It is a writing suite with paraphrasing, grammar checking, plagiarism detection and citation tools at $8.33 a month billed yearly, and it is the only tool on this page that competes with Grammarly on its actual job rather than on its detector. It makes no promise about clearing anything, which is the correct thing for it to do.
And a warning about pages like this one. Nearly all of page one for this query is written by humanizer vendors, and every one of them ranks itself first. We are a vendor too, which is why this page cites Grammarly's own wording with the date we read it, publishes the test result that makes the detector look worst, marks the price row we could not verify this month, and opens by telling you when not to buy anything. The only comparison that settles it is the one you run on your own paragraph, and with Grammarly that comparison is free.
Good questions
Questions people ask about the Grammarly AI detector
What is the best AI humanizer for Grammarly?
The best AI humanizer for Grammarly is one that rebuilds sentences rather than swapping words, because Grammarly's checker reads how predictable your prose is rather than which words you chose. Undetected.ai rewrites in one pass and shows our own AI-pattern score before and after, from $9 a month for 15,000 words. Undetectable.ai is cheapest at about $5 a month billed yearly. QuillBot is the closest substitute if you want a writing suite instead.
Is the Grammarly AI detector free?
Yes. The standalone checker at grammarly.com/ai-detector runs free and does not require an account, which makes it the easiest detector in the category to run on someone else's writing. The AI Detector agent inside the Grammarly product, which adds inline explanations and one-click rewrites, is a Grammarly Pro feature. Authorship, the writing-process recorder, is available on both Grammarly Free and Grammarly Pro.
Is the Grammarly AI detector accurate?
Grammarly publishes 99 percent detection accuracy and a first-place finish on RAID, an independent academic benchmark built from more than 670,000 texts. Hands-on results look different: PCWorld pasted in a short story written entirely by Google Gemini and Grammarly returned 37 percent, twice. Benchmark scores and one-off pastes measure different things, and Grammarly's own page says no AI detector is 100 percent accurate.
Can Grammarly AI detection be wrong?
Yes, in both directions, and Grammarly says so itself: its AI detector page states that "AI detection should never be used as a standalone verification method." Independent testing of AI detectors on real-world writing lands nearer 85 to 90 percent accuracy with false positives in the 8 to 15 percent range, and a Stanford study found 61.3 percent of essays by non-native English speakers were wrongly flagged.
Does Grammarly AI detector work for Turnitin?
No. They are different models trained on different data, so a clean Grammarly reading is not a Turnitin result and should not be treated as one. Grammarly is a useful free pre-check because you can run it yourself in seconds, which is more than Turnitin allows, but the only thing it tells you is what Grammarly thinks. We compared the two in detail in our Grammarly versus Turnitin write-up.
Can Grammarly AI detector be trusted?
Trust it as a signal, not a verdict, which is exactly how Grammarly frames it. Treat a high reading as a prompt to look again at your prose, and a low reading as weak evidence rather than clearance, since the checker missed a fully AI-written story badly enough in one published test to return 37 percent. What settles the question properly is provenance: drafts, version history, and Authorship if it was running.
Does Grammarly AI detector save your work?
The standalone checker is a one-off scan. Authorship is the feature that keeps a record, and it only stores data for text you paste into Google Docs or Microsoft Word after you switch it on. That matters more than anything else on this page: Authorship cannot be applied backwards to work you have already written, and it cannot be undone on work it has already recorded.
Does Grammarly AI detector actually work?
It works the way every statistical detector works, by measuring how predictable your sentences are and how much the rhythm varies, and it produces a number rather than proof. That approach genuinely catches unedited AI output most of the time and genuinely misfires on clean, plain, well-structured human writing. The half of Grammarly that does work as proof is Authorship, because it records rather than guesses.
Go deeper
Related reading
Grammarly AI detector vs Turnitin
Whether a clean Grammarly reading means anything at all in Turnitin.
Does Grammarly detect AI?
What Grammarly flags, and whether using Grammarly itself gets you flagged.
AI humanizer that actually works
Which detector claims you can verify for $0, and the test protocol.
Best AI humanizer overall
The full comparison, beyond any single detector.
Check it against Grammarly yourself, for free
Paste 400 words of real work, note Grammarly's number, run the rewrite, then check it again. This is the one detector where the whole test costs you nothing.
Meaning kept · Your own text rewritten · Saved to your history, delete any time