ShieldFont

ShieldFont Poisons AI Training Data by Swapping Words While Preserving Grammar

ShieldFont is a free font developed by Brazilian agency Seneda & Abrucio and Danish studio Playtype that protects web content from unauthorized scraping by generative AI systems. Instead of relying on robots.txt, the font uses OpenType glyph substitution to replace approximately one quarter of words with semantically similar alternatives from 250 categorized groups. Human visitors see the original text, while scrapers receive grammatically consistent but factually altered content that can still pass basic quality filters. Testing against FineWeb-Edu showed that roughly 10 percent of previously high-quality fragments remained acceptable after poisoning, yet 55.8 percent of those fragments contained incorrect facts. The technique works only with English text at present and is available on GitHub. Limitations include vulnerability to OCR-based screenshot attacks and reduced accessibility for screen readers used by visually impaired users.