missingglyph

A missing glyph is a glyph that a font does not provide for a given character. In digital text rendering, when a program encounters a Unicode code point that has no corresponding outline in the active font’s character map, it must display something in place of that character. The result is commonly referred to as a missing glyph or notdef glyph.

In font architecture, each font contains a mapping from code points to glyph outlines. If a code point is not defined in that mapping, the renderer typically falls back to the font’s notdef glyph, or to a generic placeholder. The notdef glyph is usually the first glyph in the font and may appear as a simple shape, a box, or another indicator; in some fonts, it is invisible.

Representations of missing glyphs vary by system and font. A common visual cue is a small square or a tofu box, especially for characters outside the font’s coverage. For East Asian fonts, missing glyphs are frequently shown as tofu boxes as well. In some environments, a replacement character or a generic glyph may be displayed instead.

Practical considerations include font coverage and fallback behavior. To minimize missing glyphs, documents and applications choose fonts that cover the needed character sets or implement font fallback to other fonts with broader coverage. It is important to distinguish missing glyphs from Unicode’s replacement character (U+FFFD), which signals ill-formed input rather than absence of a glyph in a font. See also notdef, tofu, font fallback.