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GPTZero vs PlagiarismCheck.org

Two fact sheets from our own research, side by side — pricing, platforms, API access and status re-checked by us rather than quoted from the vendors. GPTZero starts at $8.33, PlagiarismCheck.org at $2.08. Only GPTZero has a free tier. Both ship a public API.

GPTZeroEstimates whether text was machine-written and flags the sentencesPlagiarismCheck.orgSimilarity report and AI-text detection in one submission, wired into the usual school LMS platforms

Side by side

FactGPTZeroPlagiarismCheck.org
CategoryAI Detection & HumanizersAI Detection & Humanizers
Pricing modelFreemiumPaid
Starts at$8.33 month$2.08 month
Public APIYesYes
PlatformsWeb, API, Chrome ExtWeb, Chrome Ext, API
CompanyGPTZeroPlagiarismCheck.org
Launched20232015
Last verifiedSep 6, 2026Sep 6, 2026

What our research says

GPTZero

The most institutionally accepted of the detectors, and the sentence-level highlighting is what makes a result defensible in a conversation with a student — but no detector is evidence, and pricing this one required leaving the vendor's own site.

Pros

  • Sentence-level highlighting shows what drove the score instead of a bare percentage
  • Batch uploads and a developer API make it usable inside an existing review workflow
  • Free tier is generous enough to evaluate properly before paying

Cons

  • Prices are rendered client-side and are not readable without a browser, which makes budgeting awkward
  • API access is a paid add-on rather than part of the standard tier
  • Word-metered quotas punish long documents disproportionately
  • Detection accuracy remains contested and the tool cannot prove authorship

PlagiarismCheck.org

The selling point is that one submission answers both questions a teacher has — was this copied, and was this generated — instead of running two services. Ten years of operation and real LMS plugins put it ahead of the many single-page detectors that appeared in 2023. Treat the accuracy claim with the scepticism every AI detector deserves: the underlying signals are statistical and non-native writers get flagged disproportionately across this whole category.

Pros

  • Plagiarism and AI detection run on a single upload rather than two separate tools
  • Sentence-level output shows which passages triggered the score, not just a document percentage
  • Genuine LMS integrations across seven platforms, plus a Google Docs add-on and Chrome extension
  • OCR handles scanned or photographed submissions
  • Documented API for business use

Cons

  • The published '99% accuracy' figure is the vendor's own and is not independently verified
  • Institutional pricing is quote-only; the pricing page shows no numbers at all
  • No company jurisdiction is disclosed, which matters for student-data processing
  • AI detectors as a class produce false positives on formulaic and non-native writing

Which one fits

Choose GPTZero if you need

  • Schools and universities that need a defensible second opinion, not a verdict
  • Editors screening freelance submissions at volume
  • Teams wanting provenance reporting on documents they commissioned

Choose PlagiarismCheck.org if you need

  • Teachers and departments already inside Canvas, Moodle or Google Classroom
  • Editors who need a similarity report and an AI-likelihood read in the same pass
  • Institutions that need OCR because submissions arrive as photographs

More comparisons

All PlagiarismCheck.org alternatives →Browse all AI Detection & Humanizers →