UX Principles
WCAG 3.1.5
Readability
Write at a lower secondary education reading level when possible (WCAG AAA). Short sentences, common words, one idea per paragraph. Flesch-Kincaid Grade 8 or below is a good target.
In plain terms
Write plainly — short sentences and common words — so the widest audience understands on the first read.
Why this matters
Dense, complicated writing shuts out people with cognitive disabilities, lower literacy, and non-native speakers — a large share of any audience. Plain writing is one of the highest-impact accessibility moves you can make.