Obel Mono Masked: A typeface that keeps a secret

Obel Mono Masked is a typeface designed to hide credentials from people or software observing a screen, such as during screen sharing, in recordings, or in screenshots. Its central idea is to put secret detection in the font rather than requiring every application to install a plugin or adopt a special feature. Fonts contain shaping rules that can substitute one glyph for another; this design uses those rules to render parts of recognized keys as dots. Because text may be typed or generated one character at a time, the font cannot wait for a whole key and then hide it without briefly exposing it. Instead, each substitution relies only on characters already entered, so the display is correct at every point and previously drawn characters never need to change.

To recognize secrets without memory or looking ahead, the font marks a detected start with an underscore glyph that looks identical to an ordinary underscore but carries a hidden shaping distinction. It leaves the next four characters visible for identification, then masks later characters when the hidden marker and recent character sequence indicate they belong to the secret. The design covers 205 key prefixes from 82 issuers, including services such as GitHub, OpenAI, AWS, Stripe, Slack, and GitLab, and 691 contextual forms that signal a secret, such as environment-variable names, password fields, and bearer authorization headers. The approach depends on the font’s backward-looking rules and on applications displaying text with that font.