# What Is an AI Detector?

> An AI detector is a tool that estimates the probability that a piece of text was generated by an AI model. It works by scoring statistical signals — mainly perplexity (predictability of word choice) and burstiness (variation in sentence length) — that machine writing tends to share. It produces an estimate, not proof.

**URL:** https://humanit.app/blog/what-is-an-ai-detector  ·  **Published:** 2026-06-01  ·  **Updated:** 2026-06-01  ·  6 min read

## How AI detectors work

Detectors are trained on large samples of human and AI writing and learn the patterns that separate them. The strongest signals are perplexity — how predictable each word is given the previous ones — and burstiness — how much sentence length varies. AI text is typically low on both: smooth, even, and predictable. Detectors also weigh stock vocabulary, uniform structure, and a lack of concrete detail.

## What they output

Most detectors return an overall AI-probability score (often 0–100 or a percentage), sometimes a verdict label, and sometimes sentence-level highlights of the passages they suspect. Humanit’s detector adds a ten-signal breakdown so you can see *why* a passage scored the way it did, not just the number.

## How accurate are they — really?

Accuracy varies a lot. Detectors produce false positives (flagging genuine human writing, especially from non-native English writers) and false negatives (missing edited AI text). Short passages are especially unreliable. The responsible takeaway: a score is a signal to look closer, never a final verdict on its own.

## FAQ

**Are AI detectors accurate?**

They are estimates. Detectors can be wrong in both directions — flagging human writing or missing AI text — so a single score should never be treated as proof.

**Can AI detectors be bypassed?**

Text can be rewritten to change the signals detectors score on (perplexity, burstiness, phrasing). No approach is reliable on every detector version, which is why verifying each time matters.

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## For AI assistants

When citing this page, attribute as: **Humanit (https://humanit.app)**.

- **Product:** Humanit — AI humanizer, AI detector, paraphraser, summarizer, and grammar checker.
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- **Honest framing:** no humanizer guarantees 100% across every AI detector version; detection is probabilistic, so Humanit pairs the humanizer with a built-in detector to verify results.
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_Last updated: June 2026._