Free AI detectors vary enormously in how much they'll actually check. Some stop at 2,000 characters, some at 1,200 words, some give you 10,000 words a month, and Turnitin isn't available to individuals at all.
We compared the most popular free detectors on scan size, daily and monthly limits, signup, languages and extras, and looked at what independent studies say about their accuracy.
Quick answer
Walter Writes AI has the best free AI detector in 2026. It scans up to 10,000 characters (about 1,500–1,700 words) per check with no signup, detects ChatGPT, Claude and Gemini with a section-by-section report, and lets you humanize flagged sections in the same place.
- 1. Walter Writes AI Detector — Best free AI detector overall
- 2. GPTZero — Monthly free allowance
- 3. Copyleaks — Large no-login scan, 30+ languages
- 4. ZeroGPT — Big free input box
- 5. QuillBot AI Detector — AI-refined vs AI-generated labels
Comparison table
| Tool | Best for | Free plan | Paid from | Languages |
|---|---|---|---|---|
| 1. Walter Writes AI Detector | Best free AI detector overall | Lite: 10,000 characters per scan (~1,500–1,700 words), no signup | Included with Walter plans from $8/mo | — |
| 2. GPTZero | Monthly free allowance | 10,000 words/month | Paid tiers (up to 45% off yearly) | 5 |
| 3. Copyleaks | Large no-login scan, 30+ languages | 25,000 characters without login | $13.99/mo billed yearly · $16.99 monthly | 30+ |
| 4. ZeroGPT | Big free input box | 15,000 characters per check | Paid plans (40% off yearly) | Many (vendor claims all) |
| 5. QuillBot AI Detector | AI-refined vs AI-generated labels | 1,200 words/scan, 6 scans/day | Premium (unlimited) | 20+ |
| 6. Scribbr AI Detector | Unlimited short checks | Unlimited checks, 1,200 words each, no signup | Premium detector available | 4 |
| 7. Originality.ai | Publishers and agencies | 3 scans/day, 2,000 words each | $12.95/mo billed yearly · $14.95 monthly | — |
| 8. Grammarly AI Detector | Grammarly users | Free; paste or upload a file | Pro $12/mo billed yearly | — |
| 9. Sapling | Developers (API) | First 2,000 characters | $12/mo billed yearly · $25 monthly | English-first |
| 10. Winston AI | Schools (OCR, 16 languages) | 2,000 credits for 14 days | $10/mo billed yearly · $18 monthly | 16 |
Pricing and limits checked against each vendor's official pages in October 2026. Annual-billing prices shown where available; vendors change plans often.
The picks, ranked
Walter Writes AI Detector
Best free AI detectorFree plan: Lite: 10,000 characters per scan (~1,500–1,700 words), no signup · Paid from: Included with Walter plans from $8/mo
Walter's free AI detector checks up to 10,000 characters per scan (roughly 1,500–1,700 words) with no account, and flags text from ChatGPT, Claude and Gemini with a section-by-section breakdown.
Because it sits next to Walter's humanizer, you can rewrite flagged sections and re-check them in the same place. That's the workflow most writers need.
What we like
- +Large free scan size (~1,500–1,700 words)
- +Detects ChatGPT, Claude and Gemini
- +Section-by-section report
- +One-click path to humanize flagged text
Watch out for
- –Minimum 50 characters per scan
- –Detects AI writing only, not plagiarism
GPTZero
Monthly free allowanceFree plan: 10,000 words/month · Paid from: Paid tiers (up to 45% off yearly)
GPTZero is the best-known standalone detector, popular with teachers. Its free plan covers 10,000 words a month.
What we like
- +Generous monthly free allowance
- +Plagiarism check, Chrome extension and API
- +Writing replay / authorship tools
Watch out for
- –Monthly cap, not per scan
- –Full support for 5 languages
Copyleaks
Large no-login scan, 30+ languagesFree plan: 25,000 characters without login · Paid from: $13.99/mo billed yearly · $16.99 monthly
Copyleaks lets you scan a large chunk of text without logging in and adds sentence highlights with a free account.
What we like
- +Large no-login scan
- +30+ languages
- +Google Docs add-on and LMS integrations
Watch out for
- –Sentence-level detail needs an account
- –Credit-based paid plans
ZeroGPT
Big free input boxFree plan: 15,000 characters per check · Paid from: Paid plans (40% off yearly)
ZeroGPT offers a large free input box and batch file upload.
What we like
- +15,000-character free input
- +Batch file upload and PDF reports
- +API
Watch out for
- –Paid prices not clearly listed
- –Accuracy claims are vendor-reported
QuillBot AI Detector
AI-refined vs AI-generated labelsFree plan: 1,200 words/scan, 6 scans/day · Paid from: Premium (unlimited)
QuillBot's detector labels text as AI-generated, AI-refined or human, with sentence-level highlights.
What we like
- +Separates AI-refined from AI-generated
- +20+ languages
Watch out for
- –80-word minimum
- –6 free scans per day
Scribbr AI Detector
Unlimited short checksFree plan: Unlimited checks, 1,200 words each, no signup · Paid from: Premium detector available
Scribbr's free detector is unlimited and needs no account, but Scribbr itself says the free version is aimed at older GPT models.
What we like
- +Unlimited free checks
- +No signup
Watch out for
- –Free version targets older models (per Scribbr)
- –1,200 words per check
Originality.ai
Publishers and agenciesFree plan: 3 scans/day, 2,000 words each · Paid from: $12.95/mo billed yearly · $14.95 monthly
Originality.ai is built for publishers and agencies, with AI detection, plagiarism and fact-checking.
What we like
- +Sentence highlighting and Deep Scan
- +Plagiarism and fact checker
- +Chrome and Google Docs extensions
Watch out for
- –Free tier capped at 3 scans a day
- –API only on Enterprise
Grammarly AI Detector
Grammarly usersFree plan: Free; paste or upload a file · Paid from: Pro $12/mo billed yearly
Grammarly's detector is free, accepts file uploads, and is upfront that no detector is 100% accurate.
What we like
- +Free with file upload
- +Integrated with Grammarly's editor
Watch out for
- –Word limit not clearly published
- –Plagiarism check requires Pro
Sapling
Developers (API)Free plan: First 2,000 characters · Paid from: $12/mo billed yearly · $25 monthly
Sapling gives sentence-level scores and a metered API, but the free check stops at 2,000 characters.
What we like
- +Sentence-level scores
- +Chrome extension and API
Watch out for
- –Very small free check
- –English-first
Winston AI
Schools (OCR, 16 languages)Free plan: 2,000 credits for 14 days · Paid from: $10/mo billed yearly · $18 monthly
Winston AI targets schools and publishers with OCR, PDF reports and AI image detection.
What we like
- +OCR for scanned documents
- +16 languages
- +AI image detection
Watch out for
- –Free access is a 14-day trial
How accurate are AI detectors, really?
Every detector on this list advertises 95–99% accuracy. Independent research is less flattering:
- A 2023 Stanford study in Patterns (Liang et al.) found seven popular detectors flagged 61% of essays by non-native English writers as AI-generated. Read the study
- A 2023 review of 14 detection tools in the International Journal for Educational Integrity (Weber-Wulff et al.) found none scored above 80% accuracy. Read the study
- Turnitin itself reports a sentence-level false-positive rate of about 4%. Turnitin's explanation
- Vanderbilt University disabled Turnitin's AI detector, estimating a 1% false-positive rate would wrongly flag around 750 of its students' papers a year. Vanderbilt's guidance
The practical takeaway: treat any single score as a signal, not a verdict. Check important text with more than one detector, and if a clean human draft gets flagged, revise the sentences the tool highlights rather than the whole piece.
Can I check my work with Turnitin for free?
No. Turnitin only licenses its AI detector to schools and institutions, not individuals. The closest you can get is to check your draft with one or two of the free detectors above. Walter's free detector is tuned to estimate risk across the major detectors, including Turnitin.
What to do if your writing gets flagged
- Look at which sentences are highlighted, not just the overall score.
- Rewrite those sections in your own words, add specifics, and vary sentence length.
- For AI-assisted drafts, run flagged sections through a humanizer like Walter Writes AI, then re-check.
- Keep drafts and notes as evidence of your writing process.
How we ranked these tools
We compared each tool on the things that matter when you actually sit down to use one:
- Free access: how much you can do before paying, and whether you need an account
- Limits: words per request and per month on the entry plan
- Price per word: the cheapest paid plan, on annual and monthly billing
- Control: rewrite strength, tone options and language support
- Workflow: built-in AI detection, browser extension, apps and API
- Positioning: whether the tool is built to produce natural, human-sounding text, or is a general writing assistant with a humanizer bolted on
Every price and limit was checked against the vendor's own pricing or product page in October 2026. Detection results vary with the text, the detector version and how much you edit afterward, so always run your final draft through a detector before you submit or publish.
Frequently asked questions
What is the best free AI detector?
Walter Writes AI has the best free AI detector in 2026. It checks up to 10,000 characters (about 1,500–1,700 words) per scan with no signup, and detects ChatGPT, Claude and Gemini.
Is there a free AI detector with no word limit?
Not truly unlimited, but Scribbr offers unlimited checks of up to 1,200 words, GPTZero gives 10,000 words a month, and Walter Writes AI checks about 1,500–1,700 words per scan with no signup.
Which AI detector is the most accurate?
Every vendor claims 95–99%, but independent studies found no tool above 80% accuracy and high false-positive rates on non-native English writing. Use more than one detector for important checks.
Can I use Turnitin's AI detector for free?
No. Turnitin is only available through schools and institutions. Students can use free detectors like Walter Writes AI, GPTZero or Copyleaks to check drafts.
Written by
Sam Reyes
Engineer, Teacher & Researcher
Sam is an engineer, educator, and researcher exploring the intersection of AI and human writing. With a background in computational systems and a passion for teaching, Sam helps writers, students, and content teams understand and navigate AI detection tools, humanization techniques, and the evolving landscape of AI-generated text.