Free ShieldFont font tricks AI into reading gibberish

Brazilian creative agency Seneda & Abrucio and Danish studio Playtype have jointly developed ShieldFont, a free font that keeps web text readable to humans while AI sees a meaningless set of words. The developers exploited the fact that humans read rendered text while most AI bots parse the raw HTML, and used the OpenType glyph substitution algorithm, which normally swaps characters for better display, to replace whole words. Substitutions are not random: a dictionary maps words to grammatically matching alternatives, sorting them into 250 groups considering factors like abstract concepts and plural forms, replacing about a quarter of the words. This grammatical fidelity matters because AI training data collectors often run text through quality filters that reject obvious gibberish; the authors tested against the FineWeb-Edu filter and found roughly 10% of transformed texts pass, and in 55.8% of cases the meaning changes beyond recognition. The solution has drawbacks: it does not affect bots that use OCR on rendered pages, and it does affect screen readers used by visually impaired people, which also rely on HTML. ShieldFont ships with a component to recover the original text, currently works only with English text, is available on GitHub, and requires a React library component for site integration.