Decoy Font: a typeface that hides your typing from AI readers

What the experiment does

Mixfont, a project working on font tooling, has published an experiment called Decoy Font: a TrueType font in which every letter prints a decoy glyph alongside the character you actually typed. The typeface is free to use in personal, commercial and client work, and its letterforms are derived from DejaVu Sans Mono, with the full terms set out in the font's licence.

How the illusion works

The font is built on the technique behind hybrid images, the optical illusion made famous by the blended portrait of Albert Einstein and Marilyn Monroe. Two spatial frequencies share the same space: the foreground is drawn as thin outlines, while the background is a blurred, low-frequency mass. Which letter you perceive depends on how you look at it — squinting or moving further from the screen reveals the hidden message, while reading up close shows the decoy.

Machine vision works in the opposite direction. Models that read text from a screenshot inspect the pixels up close, and at that distance the sharp foreground dominates, so the model reports the decoy instead of the real sentence. Mixfont says the effect is strong enough to mislead advanced systems as well, naming the models it tested as GPT Sol and Gemini 3.5 with Thinking, plus a plain screenshot of the installed font.

Why anti-AI fonts are drawing interest

The experiment belongs to a small but growing field of "anti-AI fonts" — typefaces meant to keep text intended for people away from automated scrapers and OCR pipelines. As models become better at reading text inside images, Mixfont argues, spatial-frequency tricks offer one way to keep a message legible to humans while making it hard to extract by machine. The company has published the font for download and describes it as one of several experiments in that direction.