GPTZero vs Grammarly's AI Detector: the 14 fields and the evidence side by side
GPTZero carries 12 study records in the index and Grammarly's AI Detector carries 0, the widest evidence gap on the compare hub, by the count compiled on 9 November 2026 from the papers linked in the studies index. The two tools also share a corporate home: GPTZero announced on 23 June 2026 that it plans to join Superhuman, and Grammarly's footer reads "2026 (c) Superhuman Platform" with a Company menu that lists Superhuman and GPTZero (gptzero.me, grammarly.com/ai-detector, read 8 November 2026). The two cards are read side by side below on the same 14 fields.
Updated Fields checked 8 November 2026
Short answer
GPTZero has been tested in 12 published studies indexed here, with false positive results from 0.00% at threshold 0.5 (RAID 2024) to 9 false accusations in 18 human texts (Weber-Wulff 2023); no study in the index tested Grammarly's AI Detector, whose "99% detection accuracy" and "#1 on RAID's independent benchmark" are the vendor's own statements (grammarly.com/ai-detector, read 8 November 2026). GPTZero states 5 languages, an API, a 10,000-word free plan and premium plans from $12.99 a month; Grammarly states no language list, no API, a free detector with no published allowance, and the detector agent inside Pro at $12 a member a month billed annually or $30 monthly (gptzero.me, grammarly.com/plans, read 8 November 2026). No detector score should be the only evidence in a misconduct or hiring decision.
How do GPTZero and Grammarly compare on the 14 fields?
| Field | GPTZero | Grammarly |
|---|---|---|
| 1. Name, vendor, official domain | GPTZero, GPTZero LLC, gptzero.me | Grammarly's AI Detector, Grammarly, grammarly.com |
| 2. Modalities detected | text, image (AI Vision, specs not published) | text |
| 3. Generators covered | Claude, ChatGPT, GPT-3, GPT-4, GPT-5, GPT-6, Gemini, Llama, Deepseek, Grok, AI services based on those models | ChatGPT, GPT-6, Gemini, Claude, Microsoft Copilot, Grammarly, other tools |
| 4. Languages supported | 5: English, German, Portuguese, French, Spanish | |
| 5. Input limits | Widget: 10,000 characters per scan without an account; with a free account texts up to 150,000 characters or a batch of up to 250 files; file types and size not published | |
| 6. Free tier | Free plan covering 10,000 words per month (vendor blog, 25 October 2026); 10,000 characters per scan without login | Free AI Detector, no sign-up, allowance per period not published; on the plans page the "Detect AI generated text" row is unchecked for Free and checked for Plus and Pro |
| 7. Paid plans | Premium plans starting at $12.99/month (vendor blog); Professional Team Plan 500,000 words per member per month, minimum 2 seats, price not rendered | Pro $12 USD a member a month billed annually, $30 billed monthly, with access to the AI Detector agent; Enterprise by contact through Superhuman Go |
| 8. API | Yes, docs.gptzero.me | |
| 9. Integrations | Chrome Extension (Gmail, Google Docs, Classroom, social media), Google Docs, Google Classroom, Canvas, Zapier, API | Browser extension (Chrome, Safari, Firefox, Edge), Grammarly for MS Office, Grammarly for Google Docs, desktop (Windows, Mac), mobile (iPhone, iPad, Android) |
| 10. Vendor accuracy and false positive claims | "An accuracy rate of 99.9% when spotting AI-generated text vs. human writing, validated on RAID, detecting 95.7% of AI texts while only incorrectly predicting 1% of human texts as AI"; GPTZero 4o post, 18 October 2026: "false positive rate of only 1 in 10,402" on student writing | "Achieves 99% detection accuracy and ranks #1 on RAID's independent benchmark"; "Reduced false positives: Designed to avoid wrongly flagging human-written text", no numeric rate |
| 11. Independent studies | 12 records: Weber-Wulff 2023, Liang 2023, Walters 2023, Elkhatat 2023, Perkins 2024, RAID 2024, Chaka 2023, Krishna 2023, Orenstrakh 2023, Jabarian and Imas 2025, Van Vlasselaer 2026, Pegoraro 2023 | 0 records |
| 12. Data retention and privacy statement | Privacy policy (20 May 2026) lists submitted content as collected data; FAQ: API inputs not stored, dashboard inputs stored and used in aggregate; FERPA, GDPR and CCPA compliance stated; deletion on request | |
| 13. Launch year and ownership | 2023; GPTZero LLC; announced 23 June 2026 that GPTZero plans to join Superhuman; footer Company menu lists Superhuman and Grammarly | Not stated; Superhuman Platform (footer "2026 (c) Superhuman Platform"; Company menu lists Superhuman and GPTZero) |
| 14. Rankings the card appears in | Independently tested, false positive rate, free tiers, languages, input limits, adversarial robustness, false negative rate, claim vs evidence gap, studies by content type, platform integrations | Platform integrations |
Which studies tested both GPTZero and Grammarly?
None. No record in the studies index ran Grammarly's AI Detector, so the table below sets GPTZero's measured results beside Grammarly's own statements, labelled as vendor statements, so the two columns are never read as the same kind of number. Grammarly's claim to rank first on RAID refers to the public RAID leaderboard; the RAID 2024 record in this index covers the paper's twelve detectors, which include GPTZero and not Grammarly (arXiv 2405.07940, read 8 November 2026). One caveat belongs beside Grammarly's column: its own page says the detection model "was trained on tens of thousands of texts, including both human-written and AI-generated text created before 2021" (grammarly.com/ai-detector, read 8 November 2026).
| Source | GPTZero | Grammarly |
|---|---|---|
| Vendor statement, grammarly.com (read 8 November 2026) | "99% detection accuracy", "#1 on RAID's independent benchmark"; no false positive rate; "No AI detector is 100% accurate" | |
| Weber-Wulff 2023, 54 documents | 29 of 54 correct (54%, rank 8 of 14); 9 false accusations in 18 human documents; 3 of 36 AI documents undetected | Not tested |
| Liang 2023, 91 TOEFL and 88 US essays | One of seven detectors averaging a 61.22% false positive rate on TOEFL essays; per-detector rates in a chart only | Not tested |
| Walters 2023, 126 documents | 81% correct (Pro), 2% of 42 human papers flagged; 98% on GPT-3.5 papers, 57% on GPT-4 | Not tested |
| Elkhatat 2023, 35 paragraphs | GPT-3.5 sensitivity 93% (14 of 15), 1 false positive in 5 human controls; GPT-4: 4 of 15 flagged | Not tested |
| Perkins 2024, 114 samples | Baseline mean accuracy 26.3%, lowest of seven; 1 false accusation in 10; 58 of 104 AI samples undetected | Not tested |
| RAID 2024, shared benchmark | False positive rate 0.03% at threshold 0.25 and 0.00% at 0.5; 98.8% accuracy at 5% FPR on open-source chat models, 9.4% on non-chat models with sampling | Not tested |
| Chaka 2023, 21 responses and 30 translations | 8 of 21 English responses classified AI, 10 as human, 3 indecisive; all 30 machine-translated responses classified human | Not tested |
| Krishna 2023, 3,000 Wikipedia prompts | 13.9% of GPT-2 XL text detected at 1% FPR, falling to 1.2% after one DIPPER paraphrase | Not tested |
| Orenstrakh 2023, 164 submissions | 54.39% on 114 human submissions, 52 false positives; 20% of 10 after QuillBot | Not tested |
| Jabarian and Imas 2025, 9,960 passages | False positive rate 0.0071 on 1,992 human passages; false negative rate 0.0020 to 0.0296 before and 0.2552 to 0.7730 after StealthGPT rewrites | Not tested |
| Van Vlasselaer 2026, 160 papers | 70% of 40 fully AI papers scored under 20%; 0 of 40 hybrid papers within range; all 40 human papers correct | Not tested |
| Pegoraro 2023, ChatGPT and human Q&A benchmark | True positive rate 27.3% and true negative rate 93.5% in a 20-method sweep, March 2023 (Table I) | Not tested |
Results as each study reports them: arXiv 2306.15666, arXiv 2304.02819, De Gruyter 10.1515/opis-2022-0158, Springer 10.1007/s40979-023-00140-5, arXiv 2403.19148, arXiv 2405.07940, DOI 10.37074/jalt.2023.6.2.12, arXiv 2303.13408, arXiv 2307.07411, NBER w34223, DOI 10.1007/s40979-026-00226-w, arXiv 2304.01487, read 8 and 9 November 2026.
What do the two cost over 12 months?
| Plan | Monthly as stated | Annual as stated | Inclusions as stated | Checked on |
|---|---|---|---|---|
| GPTZero Free | $0 | 10,000 words per month (vendor blog, 25 October 2026); 10,000 characters per scan without login | 8 November 2026 | |
| GPTZero Premium (individual) | premium plans starting at $12.99/month | Individual plan cards did not render on 8 November 2026; the only readable figure is the vendor blog's starting price | 8 November 2026 | |
| GPTZero Professional Team Plan | Annual (Save 45%) / Monthly, price not rendered | 500,000 words per member, per month; minimum 2 seats | 8 November 2026 | |
| Grammarly Free | $0 | Free AI Detector with no sign-up and no published allowance; the plans page marks "Detect AI generated text" unchecked for Free | 8 November 2026 | |
| Grammarly Pro | $30 when billed monthly | $12 USD a member a month billed annually ($144 a year by arithmetic) | Everything in Free, full-sentence rewrites, tone adjustment, 2,000 AI prompts, access to the AI Detector agent | 8 November 2026 |
| Grammarly Enterprise | Contact sales; available through Superhuman Go | 8 November 2026 |
Prices as shown on gptzero.me/pricing, the GPTZero blog, grammarly.com/plans and grammarly.com/pro, checked 8 November 2026; Grammarly names USD, GPTZero shows the symbol only. GPTZero's pricing cards require JavaScript and did not render on that date; the card notes a browser recheck before any purchase decision. Grammarly's Pro price buys a writing assistant that includes the detector, so the two monthly figures do not buy the same thing.
One of the comparisons in the compare hub. The cards are GPTZero and Grammarly, and the home board answers which AI detectors exist and who has tested them?
Which card fits which reader?
- Choose GPTZero ifyou want results that outside researchers have measured: 12 study records from 2023 to 2026, against none for Grammarly (studies index, compiled 9 November 2026).
- Choose GPTZero ifyou need an API or a classroom integration: docs.gptzero.me, Canvas and Google Classroom are stated; Grammarly's detector page states no API and no LMS (gptzero.me, grammarly.com/ai-detector, read 8 November 2026).
- Choose Grammarly ifyou already pay for Grammarly Pro and want a detector inside the editor you write in: the Pro plan lists access to the AI Detector agent, and the integrations cover Word, Google Docs, four browsers, desktop and mobile (grammarly.com/pro, read 8 November 2026).
- Choose GPTZero ifyour texts are in German, Portuguese, French or Spanish: those four are stated beside English, while Grammarly publishes no language list for the detector (gptzero.me, read 8 November 2026).
- Choose GPTZero ifyou check long documents: 150,000 characters per text with a free account; Grammarly publishes no input limit for the detector (gptzero.me/faq, read 8 November 2026).
- Choose Grammarly ifyou want a free check with no account and accept that no allowance and no study result is published for it; Scribbr and QuillBot, two other free detectors on the index, are compared in the ZeroGPT vs Scribbr vs QuillBot page.
How does the evidence compare, tool by tool?
GPTZero
- Register ID
- AIDI-D-0001
- Study records
- 16 in the index: Weber-Wulff 2023, Liang 2023, Walters 2023, Elkhatat 2023, Perkins 2024, RAID 2024, Chaka 2023, Krishna 2023, Orenstrakh 2023, Jabarian and Imas 2025, Van Vlasselaer 2026, Pegoraro 2023, Kar 2024, Alshammari and Rao 2025, DAMAGE 2025, Epoch AI 2026
- Shared with Grammarly
- 0
- Vendor accuracy claim
- An accuracy rate of 99.9% when spotting AI-generated text vs. human writing, validated on RAID, detecting 95.7% of AI texts while only incorrectly predicting 1% of human texts as AI; mixed documents with a 96.5% accuracy rate. (FAQ)
- Free tier
- Free plan covering 10,000 words per month (vendor blog, Oct 25, 2026); 10,000 characters per scan without login
- Languages
- 5 stated
Grammarly
- Register ID
- AIDI-D-0008
- Study records
- 0 in the index
- Shared with GPTZero
- 0
- Vendor accuracy claim
- Achieves 99% detection accuracy and ranks #1 on RAID's independent benchmark, outperforming other leading AI detectors.
- Free tier
- Free AI Detector, no sign-up needed; allowance per period not published. On the plans page the Detect AI generated text row is unchecked for Free and checked for Plus and Pro.
- Languages
- Not stated
How this comparison is built
- Fields
- The 14 fields of every card, in card order
- Shared study records
- 0
- Fields checked
- 8 November 2026
- Records in the studies index
- 35 records
Both columns are drawn from the same 14 fields in the index data file, read on 8 November 2026 from the vendor page recorded on each card, and from the studies index, where each result is copied as the paper reports the figure, with the base stated. Where Grammarly's card has no published value, the cell is empty rather than filled with a guess, and the evidence table labels Grammarly's column as vendor statements. The shared ownership is recorded from the two vendors' own footers and announcements and is set out with every other shared owner on the which AI detectors share an owner page. The rules, the recheck schedule (next pass 8 December 2026) and the correction route are on the methodology page; the independently tested ranking sorts every card on the study count used in the first sentence.
A second GPTZero pair with shared evidence is the Sapling vs GPTZero comparison: Liang 2023, Walters 2023 and Kar 2024 tested both, read 10 November 2026.
Where each figure comes from
Values as each vendor states them on gptzero.me, gptzero.me/faq, gptzero.me/pricing, gptzero.me/privacy-policy.html, the GPTZero blog, grammarly.com/ai-detector, grammarly.com/plans and grammarly.com/pro, all read 8 November 2026. An empty cell means the card has no published value for the field: Grammarly's detector page states no language list, no input limit, no API and no retention clause for submitted text.
Questions about GPTZero and Grammarly
Are GPTZero and Grammarly the same company?
The two sites point to one platform: GPTZero announced on 23 June 2026 that it plans to join Superhuman, and Grammarly's footer reads "2026 (c) Superhuman Platform" with GPTZero in its Company menu (gptzero.me, grammarly.com/ai-detector, read 8 November 2026). The two detectors keep separate pages, prices and claims.
Has any study tested Grammarly's AI Detector?
None of the 35 records in the studies index ran it, as compiled on 9 November 2026. Grammarly's "99% detection accuracy" and its RAID ranking are vendor statements (grammarly.com/ai-detector, read 8 November 2026).
How many studies tested GPTZero?
Twelve indexed records, from Weber-Wulff 2023 to Van Vlasselaer 2026, the most of any card in the index (independently tested ranking, compiled 9 November 2026).
Which has the lower false positive rate?
Only GPTZero has a measured one: 0.00% at threshold 0.5 in RAID 2024, 0.0071 of 1,992 passages in Jabarian and Imas 2025, 2% of 42 in Walters 2023 and 9 of 18 in Weber-Wulff 2023 (arXiv 2405.07940, NBER w34223, read 8 and 9 November 2026). Grammarly publishes no rate.
Which costs less per month?
GPTZero's premium plans start at $12.99 a month per the vendor blog of 25 October 2026; Grammarly Pro is $12 a member a month billed annually or $30 monthly (gptzero.me, grammarly.com/plans, checked 8 November 2026). Grammarly's price buys a writing assistant with the detector inside it, so the two are not like for like.
Does Grammarly's free detector have a limit?
The page states none, and the plans page marks "Detect AI generated text" as unchecked for Free and checked for Plus and Pro (grammarly.com/plans, read 8 November 2026). GPTZero states 10,000 words a month on its free plan.
Does either work in Google Docs?
Both: GPTZero through its Chrome extension and Google Docs integration, Grammarly through Grammarly for Google Docs (gptzero.me, grammarly.com/ai-detector, read 8 November 2026).
Sources and revisions
Sources
- GPTZerogptzero.me
- GPTZero FAQgptzero.me/faq
- GPTZero pricinggptzero.me/pricing
- GPTZero blog, 25 October 2026gptzero.me/news/best-ai-detectors
- GPTZero 4o launch postgptzero.me/news/introducing-gptzero-4o
- GPTZero privacy policygptzero.me/privacy-policy.html
- Grammarly AI Detectorgrammarly.com/ai-detector
- Grammarly plansgrammarly.com/plans
- Grammarly Programmarly.com/pro
- Weber-Wulff et al. 2023arxiv.org/pdf/2306.15666
- Dugan et al. 2024 (RAID)arxiv.org/pdf/2405.07940
- Walters 2023degruyterbrill.com/document/doi/10.1515/o...
- Jabarian and Imas 2025 (read 9 November 2026)nber.org/papers/w34223
- Pegoraro et al. 2023 (read 9 November 2026)arxiv.org/abs/2304.01487
