GPTZero is the most widely used AI detector: paste text or upload a file and it flags likely AI-generated passages with sentence-by-sentence highlighting across GPT, Gemini, Claude and other major models.
The Writing Report adds the reverse direction – verifiable proof that a document was written by a human, which educators use for integrity workflows. The free plan covers everyday checks; Premium (from $12.99/month annually) lifts scan limits to 300,000 words and adds plagiarism detection and API access.