Grammarly AI detector explained
The Grammarly AI detector gives a percentage of your text that looks AI-generated, free on the web and built into Pro. Textlume gives a score with a range, a confidence rating and a mark on every sentence. Here is how the two compare, with Grammarly's side taken from its own pages and help articles.
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The short answer
Choose Grammarly if you already pay for Pro for grammar and tone, or if you want Authorship to record how you wrote. Choose Textlume if detection is the reason you are here and you want to see which sentences push the score up, with a range and a confidence rating. We have not tested Grammarly's detector, so this page compares what each tool shows and costs, not accuracy.
Where the two really differ
- What you get back. Grammarly reports the percentage of the text that appears AI-generated. Textlume gives an overall score with a range and a confidence rating, plus a score on each sentence.
- What you pay for. Grammarly's AI detection sits inside Pro, which is priced for grammar, tone and rewrites too. Textlume sells detector words by plan, from 6.99 USD a month billed yearly.
- Its own rewrites. Grammarly's guide says text rewritten by its own agents is likely to be flagged as AI, because those rewrites come from its language model. Worth knowing if you use its rewriter and its detector on the same draft.
- Proof of process. Grammarly Authorship records how a document was written. Textlume reads the finished text only.
Grammarly and Textlume side by side
| Feature | Grammarly | Textlume |
|---|---|---|
| Free tier | Free AI detector on its website. The free plan covers spelling, grammar and tone, with 100 AI prompts a month. | 1 free run a day per tool, up to 250 words in the detector and 150 in the humanizer. No account, no card. |
| Price | Pro: $12 a month billed yearly, $60 a quarter, or $30 month to month. | From 6.99 USD a month billed yearly, or 9.99 USD month to month. |
| Words and limits | No word allowance published for the detector. Pro includes 2,000 AI prompts a month. | Detector: 50,000 to 300,000 words a month, up to 10,000 per check. Humanizer: 10,000 to 50,000 words a month. |
| Languages | No detection languages listed. The humanizer works in six languages. | 13 calibrated text languages for AI detection. Other languages get no score. |
| Published accuracy figures | Claims 99% detection accuracy and first place on the RAID benchmark. | Held-out counts per language, with sample sizes, on our accuracy page. |
| Sentence marks | A percentage for the whole text. Its AI Detector agent also marks flagged passages. | Yes. Every sentence gets a score, next to an overall score with a range and a confidence rating. |
| Humanizer | Yes, with four preset styles and a custom voice. | Yes. Academic, professional and casual tabs, and names, numbers and quotes stay as they are. |
| API | No detection API on its plans page. | On the Pro plan, for detection, humanizing, paraphrasing, summaries and grammar. |
| Plagiarism check | Yes, in Pro, against billions of web pages. | Coming soon. Not open for checks yet. |
What Grammarly and Textlume cost
Grammarly
- Free$0
Monthly
Spelling, grammar and tone, with 100 AI prompts a month.
- Pro$12
Per month, billed yearly. Monthly: $30.
Sentence rewrites, tone changes, plagiarism and AI detection, 2,000 AI prompts a month. Also sold quarterly at $60.
- EnterpriseNo public price
Price on request from sales
Everything in Pro, plus admin roles, data loss prevention and dedicated support.
Textlume
- Basic6.99 USD
Per month, billed yearly. Monthly: 9.99 USD.
50,000 detector words, 10,000 humanizer words and 10,000 paraphraser words a month, plus 20 runs of clarity suggestions a day.
- Plus9.99 USD
Per month, billed yearly. Monthly: 19.99 USD.
150,000 detector words, 25,000 humanizer words and 25,000 paraphraser words a month, plus 30 runs of clarity suggestions a day.
- Pro12.99 USD
Per month, billed yearly. Monthly: 29.99 USD.
300,000 detector words, 50,000 humanizer words and 50,000 paraphraser words a month, plus 40 runs of clarity suggestions a day. API access included.
Where Grammarly is ahead
- Authorship records how a document was written in Word, Google Docs and its own editor, and the writer decides when to share the report.
- It works inside Word, Google Docs and the browser, so the check runs where the writing happens.
- Pro bundles a plagiarism check against billions of web pages with grammar, tone and rewrite tools.
- Its support guide is frank about limits: the score is an estimate, short passages are harder, and its own rewrites can raise the score.
How Textlume works
- The detector is a tool with its own word pool, 50,000 to 300,000 words a month and up to 10,000 words in one check.
- Every sentence gets its own score, and the overall reading comes with a range and a confidence rating.
- Free checks need no account and no card.
- The detector is calibrated for 13 text languages, and our accuracy page lists how often human texts were flagged in each.
- Grammar checks are free on every plan, signed in or not.
Which one suits your work
Pick Grammarly if
you already use Grammarly Pro for grammar and tone, want AI detection and plagiarism in the same subscription, or need Authorship to show how you wrote a paper.
Pick Textlume if
AI detection is the main job and you want a sentence-by-sentence reading with a range and a confidence rating, a stated number of detector words, and a free daily check without an account.
Questions people ask before choosing
ContactIs the Grammarly AI detector free?
Yes, there is a free AI detector on Grammarly's website where you paste or upload text. In the apps, AI detection is part of Pro, and the plans page does not list it for the free plan.
How accurate is Grammarly's AI detector?
Grammarly says it achieves 99% detection accuracy and ranks first on the RAID benchmark. Its own support guide adds that the percentage should not be used as an objective source of truth and that shorter passages are harder to score. We have not tested Grammarly's detector, so we make no claim either way.
Why does Grammarly flag my own writing as AI?
Grammarly's guide gives two reasons. Some human writing has the patterns, syntax and complexity of AI text, and text rewritten by Grammarly's own agents comes from its language model, so it can raise the score. The guide suggests taking its feedback and making the changes yourself.
Will my professor see the same score as Grammarly shows me?
Not necessarily. Grammarly's guide says its model is its own and that scores may differ from Turnitin, GPTZero, Copyleaks and others. The same holds for Textlume: different detectors give different readings.
Does Grammarly show which sentences look AI-written?
The web tool gives a percentage for the whole text. Its AI Detector agent marks the passages it flags with bars beside the text. Textlume gives every sentence its own score next to the overall reading.
How much does Grammarly Pro cost?
Grammarly's support article lists $30 USD a month, $60 for three months, or $144 a year, which works out at $12 a month. Textlume Basic costs 6.99 USD a month billed yearly or 9.99 USD month to month.
What is Grammarly Authorship?
A feature that tracks how you write in Word, Google Docs or the Grammarly editor and marks each sentence's source, such as typed, pasted or AI-assisted. Grammarly says the report is shared only when you choose to share it.
Does Grammarly have a humanizer?
Yes. It offers four preset styles, a custom voice learned from a writing sample, and six languages. The Textlume humanizer keeps names, numbers and quotes as they are and makes no promise about passing any detector.
Are Grammarly and GPTZero the same company?
GPTZero announced in 2026 that it is joining Superhuman, the company that also runs Grammarly, and said nothing changes for its daily users. Grammarly's site footer now lists Superhuman and GPTZero under its company links.
Does Textlume check plagiarism like Grammarly?
Our plagiarism check is coming soon and not live yet. Once it opens, it will search the open web on paid plans. Grammarly Pro already includes one.
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