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The best free AI detectors: limits, accuracy, upgrade points

Free AI detectors differ less in their core signals than in their limits, signup requirements, and feedback detail. This list compares the most used options so you can pick the right check for your draft.

How to read this list

Every detector works from similar writing signals: uneven versus uniform sentence length (burstiness), perplexity, stock AI phrases, hedging and transition words, and repetition. The differences are in calibration, UX, input limits, and secondary features like per-sentence scoring, API access, and integrations. We cover the core signals in our guide to how AI detectors work.No free detector is perfect. They disagree with each other, and they produce false positives and false negatives. Treat every score as a signal, not a verdict.

Leap

Our tool. Free detection with no signup, running entirely in your browser, with per-sentence scoring and a humanizer path if you want to revise flagged passages. Nothing you paste is sent anywhere.
  • Strengths: sentence-level highlighting so you see exactly which lines weigh most in the score; explicit signal reasons such as hedging, stock phrases, em-dash density, and uniform sentence length instead of just a number; integration with a free humanizer.
  • Weaknesses: no API and no batch uploads.
Try it on your own draft at the Leap AI detector page.

GPTZero

One of the earliest AI detectors, launched by Edward Tian in early 2023. Free tier with signup. Strong name recognition and widely referenced in education contexts. Produces both an overall classification and per-sentence annotations.
  • Strengths: credibility, LMS integrations, browser extension.
  • Weaknesses: the free tier has word limits; it has been reported to flag non-native English more aggressively than expected.

ZeroGPT

Free, no signup, generous input limit. Simple UX: paste, score, done. Good for quick checks.
  • Strengths: the lowest-friction free tool in this list.
  • Weaknesses: fewer detailed signals, no per-sentence breakdown on the free tier, little public documentation about the underlying model.

Copyleaks

Free preview, paid for substantive use. Primarily a plagiarism platform that added AI detection. A reasonable choice if you want both checks in one tool and are comfortable with a signup flow.
  • Strengths: multi-language support, LMS plugins, oriented toward educational institutions.
  • Weaknesses: the most useful features live behind the paid tier.

Originality.ai

Free trial credits, paid after. Marketed at SEO and publishing use cases, which shows in its calibration: it is tuned for marketing content detection.
  • Strengths: widely cited in SEO circles, publishes methodology, offers an API for content operations.
  • Weaknesses: not a free tool in practice; its calibration can be aggressive on technical prose.

Turnitin AI writing indicator

Not a standalone tool. It is bundled with the Turnitin plagiarism check that schools and universities already use. Students usually cannot access it directly; teachers see the score in the similarity report.
  • Strengths: ubiquity in education.
  • Weaknesses: no public free tier, limited transparency on methodology.

Sapling AI detector

Free with generous limits, simple UX, and a browser extension. Aimed mostly at customer support and enterprise writing teams.
  • Strengths: clean integration options, reasonable calibration.
  • Weaknesses: less detailed output than tools with per-sentence breakdowns.

Writer's AI content detector

A free tool from Writer.com. Simple, fast, works without signup. Input limits are tighter than other free options. Good for quick checks of short passages.

Which to pick

If you want sentence-level detail and a humanizer path with no signup: Leap. If you want the name educators recognize: GPTZero. If you want the fastest no-signup check: ZeroGPT. If your workflow is already in a Turnitin-using institution, that is the result that matters there, but you can always cross-check a flagged paper with a second detector before raising a conversation. Our piece on AI detection accuracy explains why cross-checking makes sense.

A responsibility note

A detector score is never enough to accuse someone of AI use. Run the piece through two or three tools, read it yourself, consider the author's history, and have a conversation before drawing conclusions. Detectors are a starting point, not a verdict, and a score should never be the only basis for an accusation. Our guide to false positives goes deeper on why.

Frequently asked questions