When fonts fall | Figma Blog (opens in new tab)

Font fallback is the mechanism that lets computers display characters a font does not contain. It explains familiar problems such as missing-character boxes, broken emoji, shifted lines, inaccessible decorative “fonts,” and inconsistent kaomoji. Rather than random bugs, these effects arise from the gap between text data and the fonts available to render it.

Everyday Symptoms of Font Fallback

• Missing characters may appear as boxes, question marks, or other placeholder symbols.
• Emoji can look assembled differently across devices when platforms support different glyphs or emoji sequences.
• Decorative social-media “fonts” are often alternate Unicode characters, not actual font changes.
• These characters can create accessibility problems for screen readers and display as empty boxes on unsupported systems.
• Adding an emoji or unsupported character can change line height or spacing because a fallback font has different metrics.
• Kaomoji and other symbol combinations may render differently depending on the available fonts.

Why Fonts Cannot Contain Everything

• A glyph is the visual form used to represent a character.
• Even basic Western fonts require hundreds of glyphs for letters, numbers, punctuation, accents, symbols, ligatures, and OpenType alternatives.
• Fonts supporting Chinese, Japanese, or other writing systems may contain thousands of glyphs.
• Supporting additional languages and writing systems continually expands the required character set.
• Font designers must eventually decide which characters their font will not support.

The .notdef Glyph

• Fonts include a special last-resort glyph called .notdef, used when a requested character is missing.
• It commonly appears as a rectangle, sometimes with a cross or question mark.
• .notdef is not a Unicode character; it is a visual substitute produced by the font.
• The original character remains intact in the underlying text, so changing fonts or updating the font may reveal it correctly later.
• Designers can choose how .notdef looks, from a simple blank square to more elaborate warning-like designs.

Font Fallback as a Computer-Typography Problem

• In physical typography, a piece of metal type inherently belonged to a specific font, so this mismatch was impossible.
• Digital text can originate from another person, device, era, or font, creating a separation between the character and its visual representation.
• Font fallback exists to bridge that gap by searching for another way to render unsupported characters—or displaying .notdef when no suitable glyph is available.

Understanding font fallback makes many seemingly arbitrary typography failures predictable: the text is usually still present, but the chosen font lacks the glyph or the system’s fallback behavior differs.