DetectGPT (https://detectgpt.io) is a free AI checker for text written by ChatGPT, Claude and Gemini. It runs entirely in the browser: paste up to 3,000 words, or enter a public URL, and get a report showing what share of the writing looks AI-generated, with suspicious passages highlighted by intensity.
It works on output from ChatGPT, GPT-5, Claude, Grok and Gemini. There is no account or login required, checks are unlimited, and every result gets a shareable link. DetectGPT also includes a plagiarism/similarity checker and a humanizer tool.
It is built for students, teachers, writers and marketers who need a quick, reliable way to check whether content was written by AI. Pricing: completely free.