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GPTZero vs Undetectable AI

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, Undetectable AI at $9.99. Both have a free tier. Both ship a public API.

GPTZeroEstimates whether text was machine-written and flags the sentencesUndetectable AIRewrites machine-written drafts to read human, with detection scoring built in

Side by side

FactGPTZeroUndetectable AI
CategoryAI Detection & HumanizersAI Detection & Humanizers
Pricing modelFreemiumFreemium
Starts at$8.33 month$9.99 month
Public APIYesYes
PlatformsWeb, API, Chrome ExtWeb, API, Chrome Ext
CompanyGPTZeroUndetectable Inc.
Launched20232023
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

Undetectable AI

Buy it only if you accept that passing a detector is a moving target: detector vendors retrain constantly, and text that cleared last month can flag next month. As a multi-format detection dashboard it is more defensible than as a bypass tool.

Pros

  • Detector and rewriter run in one pass, so you see which sentences changed and why
  • Coverage extends past text into image, voice, video and document classifiers
  • Browser extension works inside Docs and Gmail rather than a separate tab
  • Entry tier is genuinely cheap at annual rates

Cons

  • Rewrites often flatten voice and add filler to break statistical patterns
  • Detection on short passages is unreliable in both directions
  • Word quotas drain fast because rejected attempts still consume them
  • The free trial caps at 250 words, barely enough to judge output quality

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 Undetectable AI if you need

  • Marketers cleaning up bulk LLM drafts before publishing
  • Editors wanting a second opinion on submitted copy
  • Teams screening images and audio for synthetic origin
  • Non-native writers smoothing register and tone

More comparisons

All Undetectable AI alternatives →Browse all AI Detection & Humanizers →