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AI Detection6 min readFebruary 20, 2026

How AI Detection Works: Perplexity, Burstiness & Probability

Learn the core metrics behind AI detectors: perplexity, burstiness, and token probability distributions.

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The Mathematics of Detection

AI detectors evaluate two primary mathematical metrics:

  • Perplexity: A measure of how likely a word is to follow the previous word. Low perplexity indicates standard AI predictability.
  • Burstiness: The variation in sentence length and structure across a document. High burstiness is typical of human writing.

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