readability

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# Readability

> **Definition.** Readability is the ease with which sustained text can be read — paragraphs, articles, documentation, long-form content. It depends on the legibility of individual characters (necessary precondition) plus a set of prose-specific factors: line length, line height, paragraph spacing, typeface suited for sustained reading, and visual breathing room. A readable design lets the reader move smoothly through the text without fatigue or visual jumping.

Readability is distinct from *legibility*. Legibility is per-character clarity — can the user identify each letter at a glance. Readability is sustained-reading ease — can the user read paragraphs of prose comfortably without tiring.

A typeface can be highly legible (every character distinguishable) but poorly readable (uncomfortable for long-form reading) — many display typefaces are this way. A typeface can be highly readable (comfortable for sustained reading) but only moderately legible (some characters look similar) — many traditional book typefaces have minor character-distinction issues that don't matter for prose.

## Why readability matters

Most UI text is short — labels, buttons, helper text. Legibility usually dominates these contexts. But many products also serve long-form text: documentation, articles, emails, transcripts, reports, books, news, dashboards with substantial commentary. For these, readability matters as much as or more than legibility.

Poor readability costs the user real effort: they tire faster, lose their place more often, miss content, and abandon longer pieces. The cost is not in any single moment but in the cumulative fatigue of reading.