Understandability – Plain Language as a Foundation of Digital Accessibility
Understandability describes the quality of text that allows as many people as possible to grasp its meaning without extra effort. In the context of digital accessibility, text understandability is not an editorial bonus, it is an access requirement: content that is linguistically overloaded actively excludes people with cognitive impairments, dyslexia, or limited language proficiency.
The criteria for understandable text are clear: short sentences, common words, logical structure, no unnecessary additions or nested clauses, and concrete examples wherever technical terms are unavoidable. Simplicity and brevity are not a dumbing-down of content but a mark of quality.
The European Accessibility Act (EAA) requires WCAG 2.1 Level AA since 28 June 2025. The WCAG principle "Understandable" is its fourth foundational principle and is legally binding for many businesses across the EU.
Understandability at a Glance
- WCAG principle: Understandable – criteria 3.1, 3.2, 3.3
- Language: Short sentences, common words, no unnecessary additions
- Structure: Logical layout with headings, paragraphs, and lists
- Content: Concrete examples instead of abstract technical terms
- Legal: Part of the WCAG 2.1 obligation under the EAA since June 2025
The WCAG Principle of Understandability
The WCAG organise accessibility into four core principles: Perceivable, Operable, Understandable, and Robust. The Understandable principle covers three groups of criteria:
- 3.1 Readable: The language of the page is identified in code and unusual terms are explained
- 3.2 Predictable: Pages behave consistently and do not trigger unexpected context changes
- 3.3 Input Assistance: Error messages are clear and forms help users complete them correctly
For editorial content, criterion group 3.1 is most directly relevant. It requires, among other things, that the page language is programmatically declared and that unusual words, abbreviations, and technical terms are explained.
Characteristics of Understandable Text
Text understandability can be broken down into a small number of well-measurable criteria. Research on readability shows that sentence length, word frequency, and structure are the key factors determining how quickly a text is processed:
- Brevity: Sentences under 15 to 20 words are easier to process than long nested constructions
- Common words: Frequently used words are recognised and processed faster than rare or technical terms
- Structure: Headings, paragraphs, and lists support scanning and contextualising content
- Examples: Concrete examples anchor abstract content and support comprehension
- No filler: Redundant words, padding, and nominalised writing style slow down reading
Understandability and Plain Language
Understandability and Plain Language are related but distinct concepts. Plain Language follows a defined set of rules: very short sentences, one idea per sentence, and a strict avoidance of foreign words. It is primarily aimed at people with learning disabilities or very limited language proficiency.
Understandability is the broader concept: it describes the general goal of writing text that the widest possible audience can grasp without effort, without necessarily following the strict rules of Easy-to-Read Language. Both approaches complement each other and serve different audiences along the spectrum of language accessibility.
SiteCockpit Solution
easyMonitoring: Systematically identify language-related accessibility issues
easyMonitoring automatically checks your website for WCAG violations affecting understandability: missing language declaration in code (WCAG 3.1.1), unexplained abbreviations, and unclear error messages in forms (WCAG 3.3). You receive a score from 0 to 100, plus a detailed report with exact locations and guidance on how to fix each issue.
Discover easyMonitoring →Frequently Asked Questions about Understandability
From what reading level is a text considered understandable?
There is no single legal reading level for general web content. A common benchmark is B1 to B2 on the Common European Framework of Reference for Languages: texts at this level are accessible to most readers without difficulty. For content explicitly targeting people with learning disabilities, the rules of Easy-to-Read Language (A1 level) apply.
Do I always need to explain technical terms on my website?
WCAG 3.1.3 recommends explaining unusual words and technical terms, especially when the target audience cannot be assumed to have specialist knowledge. An explanation can appear inline in the text, as a tooltip, in a glossary, or via a link to a definition page.
Is understandability only relevant for people with disabilities?
No. Understandable texts benefit all users: people under time pressure, those reading in a second language, older adults, and anyone scanning content on a mobile device. Understandability is a universal design principle that connects accessibility with general usability.
How does understandability differ from readability?
Readability describes the visual accessibility of text, meaning font size, line spacing, contrast, and typeface. Understandability describes the linguistic and content-level accessibility: sentence structure, word choice, organisation, and complexity. Both dimensions are necessary for accessible text and complement each other.
How understandable is your website, really?
Have your website automatically checked for WCAG violations in the area of understandability. easyMonitoring delivers a detailed report with precise locations so you can fix issues efficiently.
Try for freeRelated Topics
- Plain Language – Rule-based language concept for maximum accessibility
- Easy-to-Read Language – Strictly standardised language system for people with learning disabilities
- Dyslexia – Why understandable texts matter for people with reading and spelling disorders
- Digital Accessibility – Overview of all requirements and measures