AI Text Detector — Check If Text Is AI-Written

How AI Text Verification Works

What is an AI text detector?

An AI text detector estimates how likely it is that a piece of writing was produced by a large language model such as ChatGPT, Gemini, Claude or Llama rather than written by a person. ProofAI’s AI text detector analyses the text you paste and returns an AI probability, a human probability, an overall verdict and, where available, a sentence-level breakdown that colour-codes passages from likely human to likely AI.

It is built for people who need to review writing they did not produce themselves: teachers marking essays, editors reviewing submissions, recruiters reading cover letters and businesses checking outsourced content.

How AI text detection works

Language models write by repeatedly choosing a likely next word. That makes their output statistically different from most human writing: word choices are more predictable, sentence lengths and structures vary less, and the tone stays unusually even from start to finish. Detectors measure signals like these, often described as perplexity (how predictable the text is) and burstiness (how much it varies), alongside patterns learned from large sets of known human and AI writing.

ProofAI combines these signals into a probability for the whole text and, where the analysis supports it, for each sentence. That is why mixed documents, for example a human draft polished with AI or an AI draft edited by a person, often show both red and green passages.

Accuracy, false positives and responsible use

AI detection is probabilistic. Every detector, including ProofAI, can produce false positives (human writing flagged as AI) and false negatives (AI writing that passes as human). Errors are more likely with short texts, formulaic writing such as technical or legal templates, text that has been heavily paraphrased, and writing by non-native English speakers, a group that independent research has found to be flagged more often by AI detectors. If you are checking text in a language other than English, treat results with extra caution.

Use the result as a starting point for a conversation, never as the only evidence for a grade, penalty or hiring decision. Our education guide explains how schools can use AI detection fairly.

Privacy

Text is sent securely for analysis and is not published or shared. If you are signed in, we keep the result (scores and verdict, not your text) in your usage history so you can track your checks. Anonymous visitors do not need an account; we use a cookie, your IP address and a hashed device fingerprint only to apply the free daily limit. See the privacy policy.