Grammarly AI Detector Review (2026): Free vs Pro and a Better Pick

Grammarly AI Detector is the AI checker inside Grammarly, the writing assistant from Superhuman. The catch, as this Grammarly AI detector review shows: the free version gives one overall score, flagged sections cost extra, and Grammarly says its detector will likely flag its own humanizer's rewrites. Our top pick is Essai, a free AI detector plus an AI humanizer.

Below you'll find what Grammarly's free and paid detection includes, its prices as of October 2026, what Grammarly and outside researchers say about accuracy, what users report and how it compares with Essai. Want to check a draft now? Essai's free AI detector gives you an AI probability score, and the AI humanizer is designed to make flagged passages read naturally while keeping your meaning.

Grammarly AI Detector at a glance

Pros and cons

Pros

• A free check with file upload. Paste text or upload a .doc, .docx, .odt, .rtf, .txt, .html or .pdf file to see what share of it appears AI-generated.
• Checks where you write. Paid plans run detection in Grammarly's docs editor, in Google Docs through the browser extension and in Microsoft Word through the desktop app.
• Authorship tracks your process. On Free and Pro, Authorship records what you typed, pasted or generated with AI, and nobody sees the report unless you share it.

Cons

• One number for free. The free checker returns a single overall percentage. Flagged sections, and checks inside Google Docs and Word, need a paid plan.
• No standalone detector plan. Detailed detection comes bundled with Grammarly Pro at $30 a month, $60 a quarter or $144 a year (as of October 2026), roughly double Essai Basic's $14.99 monthly price.
• Its own humanizer gets flagged. Grammarly warns that rewrites from its Grammarly, Paraphraser and Humanizer agents will likely be flagged by its detector, and it says its humanizer "is not intended to bypass AI detectors."
• No reasons behind a flag. The AI Detector user guide says detection "doesn't explain why the text may be flagged." Phrase-level hints come from AI Rewriter, a separate paid agent Grammarly is still rolling out.
• A dated #1 claim. The detector page still says it "ranks #1" on RAID, but as of October 16, 2026, the leaderboard's default view shows three newer entries at 1.000 against Grammarly's 0.999.
• Inconsistent model details. The detector page says the model was trained on "tens of thousands of texts" created before 2021, while the help center says "hundreds of thousands."
• Strict refunds, training on by default. Refunds are issued only where the law requires, and the setting that lets Grammarly train its models on your content is on by default for individual accounts.

Key features

Grammarly's detector is one feature of a larger writing suite, and most of its depth sits on paid plans. Here is what you get and where the limits are.

The free web checker

On Grammarly's AI detector page, you paste text or upload a document, click Scan for AI and get the percentage of text that "appears to be AI-generated." Grammarly says the checker splits a document into sections and scores each one for language patterns linked to AI writing. No word limit is posted, but the help center notes that shorter passages are "slightly harder to measure," so a paragraph or two gives a shakier result than a full essay.

The AI Detector agent, Google Docs and Word

On Pro and Plus, detection becomes an agent in Grammarly's docs editor and in Superhuman Go, the company's AI assistant. The AI Detector user guide says the agent marks sections of a draft with bars in a side panel and shows how likely each part is to be flagged, with a Generate citation button for passages where you used AI on purpose.

Paid plans also add detection inside Google Docs, through a "Check for plagiarism and AI text" option in the browser extension, and inside Microsoft Word, where the Grammarly desktop apps fold AI detection into the plagiarism check. Grammarly lists both for Pro, Plus, Business and Education plans, so the free tier gets neither.

Authorship

Grammarly Authorship records how a document was written instead of judging the finished text: what was typed, what was pasted and what came from AI, shown in a color-coded report with a replay. It works in Google Docs, Microsoft Word, Grammarly's editor and Superhuman Go. Authorship documents your process, but it does nothing to improve the writing itself.

Grammarly's humanizer

Grammarly's AI humanizer page offers basic rewriting for free, and a free account adds a Humanizer agent with four preset voices and custom voice profiles built from a writing sample of 200 words or more. The limit is in Grammarly's own words: the tool "is not intended to bypass AI detectors," and the detector guide warns that Humanizer rewrites will likely be flagged.

Essai's humanizer is designed for the opposite result: to keep your meaning while making phrasing, rhythm and word choice read naturally, so AI-assisted text reads as human-written. If you're revising an AI-assisted essay, follow our step-by-step workflow, and check your course's AI policy first.

Plagiarism checks, AI Rewriter and data settings

Pro and Plus bundle a Plagiarism Checker agent, which Grammarly says compares text against over 16 billion web pages and ProQuest's academic databases, along with citation suggestions and AI Rewriter, which labels phrases that AI tends to use. That makes Pro a full writing suite, and it also means you pay for the whole suite to get Grammarly's detailed detection.

One setting is worth checking. Grammarly's Product Improvement and Training control, which lets it use your content to train its models, is on by default for Free, Premium and single-user Pro accounts. You can switch it off in your account settings.

Grammarly AI Detector pricing (as of October 2026)

The web checker is free. Detection inside Grammarly's apps comes with a paid plan, and there is no separate detector subscription. US prices below come from Grammarly's help center article on Pro pricing and its plans page, as of October 2026.

Read the billing rules before you pay:

• Renewals. Plans renew automatically at the then-current rate. You can cancel anytime and keep paid features until the billing period ends.
• Refunds. The terms call payments non-refundable to the extent the law allows, and the help center says refunds are issued only if required by law. App Store purchases go through Apple.
• Trials. Grammarly periodically offers free Pro trials. Canceling one ends it right away and switches the account to Free.
• Student discount. Eligible students can get half off Pro for a limited time through SheerID verification, but the discount covers one subscription period and only the first seat.

At standard prices, Essai costs less at both entry points: Basic is $14.99 a month, or $9.99 a month billed yearly, as of October 2026, and every paid plan includes unlimited AI detection along with the humanizer. You may not need to pay for detection at all, since a free Essai account adds detailed reports and unlimited scans. Compare plans on the Essai pricing page.

Is Grammarly AI Detector accurate?

Grammarly backs its accuracy claim with the RAID benchmark, but that benchmark measures something narrower than everyday accuracy, and Grammarly's own help center says a score is not proof.

What Grammarly claims

The detector page claims 99 percent detection accuracy and a #1 rank on RAID. In a February 2026 blog post, Grammarly said RAID tests detectors on over 670,000 texts across writing styles, AI models and attempts to fool them.

The help center is more cautious. It calls the model "directionally accurate," says it is "optimized to minimize false positives," and says the percentage should not be treated as an objective source of truth. It also notes that Grammarly's "proprietary in-house model" may score text differently from Turnitin, GPTZero or Copyleaks, so your result doesn't predict what an instructor's tool will show.

What the RAID score really measures

RAID is an academic benchmark presented at ACL 2024 (Dugan et al.). Detector makers run its test set through their own detectors and submit the predictions for scoring (project README). The default metric is the share of AI-written texts a detector catches when its threshold is set so that 5 percent of human-written texts get flagged. On that metric, with no adversarial attacks, Grammarly's entry on the RAID leaderboard scores 0.999. Three caveats apply:

• It's no longer #1. As of October 16, 2026, three newer entries display 1.000 in the default view. With RAID's 11 adversarial attacks included, Grammarly's 0.995 ranks 15th of 58 entries.
• The AI texts are older. RAID's AI-written texts come from the 11 models in its 2024 dataset, including ChatGPT, GPT-4, Llama 2 70B and Mistral 7B, so the score says little directly about newer models.
• The cutoff isn't yours. RAID sets each detector's threshold to hit its false-positive target. Grammarly's checker shows you a percentage instead, and the leaderboard doesn't say how often that percentage misreads human writing in everyday use.

What outside research says

• Bias against non-native writers. A 2023 Stanford study in Patterns (Liang et al.) ran seven widely used detectors on 91 TOEFL essays by non-native English writers. More than half were labeled AI-generated, an average false-positive rate of 61.3 percent. Grammarly's detector launched later and wasn't in the study, but Grammarly's own accuracy guide says writers using English as an additional language are "particularly vulnerable to misclassification."
• OpenAI pulled its own classifier. OpenAI retired its AI text classifier on July 20, 2023, "due to its low rate of accuracy." On its challenge set it caught 26 percent of AI-written text and labeled human writing as AI 9 percent of the time (archived OpenAI post).
• Small error rates add up. Turnitin aims for a false-positive rate below 1 percent and says its rate "is not zero." Vanderbilt University disabled Turnitin's AI detector in August 2023, noting that a 1 percent rate could have mislabeled around 750 of the 75,000 papers it submitted in 2022.

Real-world problems

Grammarly says ordinary grammar and spelling fixes should typically not affect the score, while meaningful rewrites by its generative features will raise it. Real cases show how much is at stake. Superhuman's post about GPTZero recounts a University of North Georgia student who wrote a paper with Grammarly running in the background to catch spelling and punctuation, was flagged by a different detector, failed the assignment and lost a scholarship.

If your own writing gets flagged, our guide to AI detection false positives covers what to do next, and teachers can follow a fair process for checking student essays.

Essai's AI detector returns an AI probability score from 0 to 100 percent and works best on 150 words or more. In Essai's internal testing, our detector outperformed other AI detectors on many of the criteria we track.

What users say

Public ratings cover Grammarly as a whole, not the detector alone. As of October 16, 2026:

• Trustpilot: a TrustScore of 3.1 out of 5, labeled Average, from 10,478 reviews. Grammarly invites customers to leave reviews and had replied to just under half of the negative ones.
• Chrome Web Store: the Grammarly extension showed 3.9 out of 5 from 43.2K ratings.

Trustpilot's AI-generated summary says some reviewers "were not happy with unexpected subscription charges and unclear free trial terms." Those complaints match the billing rules above: plans renew automatically, and refunds are issued only where the law requires.

What Essai users say

Essai users describe it in their own words:

"I've tested many alternatives, but nothing comes close to the quality Essai provides." (Priya Sharma, Essai user)

"The quality of the humanized text is remarkable. Essai preserves my ideas while making everything sound natural. My grades have improved significantly since I started using it." (Michael Foster, Essai user)

"Essai has revolutionized my business management studies. The text humanizer has significantly improved my reports and presentations. This all-in-one solution is a student's dream!" (David Williams, Essai user)

Grammarly AI Detector vs Essai

Grammarly's detector is one feature of a writing suite, and its detailed view sits behind a paid plan. Essai is built around two jobs: a free AI detector and an AI humanizer designed to make AI-assisted text read as human-written. Prices are as of October 2026.

Why Essai is the better Grammarly AI Detector alternative

• More for free. A free Essai account adds detailed reports and unlimited scans. Grammarly's free checker stops at one overall percentage, and flagged sections need a paid plan.
• About half the monthly price. At standard prices as of October 2026, Essai Basic costs $14.99 a month, or $9.99 a month billed yearly, against $30 a month or $144 a year for Grammarly Pro.
• A humanizer built for the job. Essai's humanizer is designed to keep your meaning while making phrasing, rhythm and word choice read naturally, so AI-assisted text reads as human-written. Grammarly says its own humanizer isn't meant to bypass detectors, and its detector will likely flag those rewrites.
• Detect and revise in one place. Essai's humanizer and detector live in the same web app, so you can humanize a draft and check it in one workflow.
• No writing suite to buy. Grammarly's detailed detection comes bundled with a full writing-suite subscription. Every Essai paid plan includes unlimited AI detection alongside the humanizer.
• Start without signing up. The humanizer's free tier handles up to 125 words per request with no signup and no credit card.

Best Grammarly AI Detector alternatives

• Essai: best overall. Our top pick for students and writers: a free AI detector with detailed reports and unlimited scans on a free account, plus an AI humanizer in the same app. Paid plans start at $14.99 a month, or $9.99 billed yearly, as of October 2026.
• GPTZero: now Grammarly's sister product under Superhuman, and still sold on its own. The free plan covers 10,000 words a month, Premium costs $23.99 a month as of October 2026, and there is no humanizer.
• Originality.ai: a credit-based detector and plagiarism checker for publishers and editors. The free tier allows three AI scans a day of up to 2,000 words each, and its help center says it offers no humanizer.
• Winston AI: a credit-based detector for educators and publishers that also checks images. The free option is a 14-day trial with 2,000 credits, and paid plans start at $18 a month as of October 2026.
• Copyleaks: pairs AI detection with plagiarism checking but has no humanizer. Paid plans start at $16.99 a month, or $13.99 billed annually, as of October 2026.

For the full ranking, see our guide to the best AI detectors.

Verdict: our Grammarly AI detector review

Grammarly's AI detector is a convenient check if you already pay for Grammarly, but on its own it falls short: the free version stops at one overall score, detailed results cost $30 a month or $144 a year (as of October 2026), and Grammarly says its detector will likely flag rewrites from its own humanizer. In our view, Essai is the best Grammarly AI detector alternative in 2026 and the best AI detector and humanizer pairing for students and writers. You get a free AI detector with detailed reports and unlimited scans on a free account, an AI humanizer designed to keep your meaning while making your writing read naturally, and paid plans from $14.99 a month, or $9.99 billed yearly. Check your draft, humanize what needs work and check it again, all in one place.