Category: WCAG Principles and Conformance

Understandable

Also known as: Understandability

Simply put

In everyday language, "understandable" means capable of being readily understood, or intelligible. In the context of digital accessibility, it refers to one of the core principles used to evaluate whether website and application content can be comprehended by the people who use it. Note that the general-dictionary evidence provided here defines the ordinary meaning of the word rather than its specialized use within accessibility standards.

Formal definition

As a general adjective, "understandable" describes something capable of being readily understood or intelligible. Within digital accessibility, "Understandable" is commonly used as the name of one of the four foundational principles of the Web Content Accessibility Guidelines (WCAG), published by the W3C's Web Accessibility Initiative, alongside Perceivable, Operable, and Robust; under WCAG, this principle generally addresses making information and the operation of a user interface understandable to users. The evidence packet supplied here supports only the ordinary-language definition and does not include the WCAG source text, so practitioners should consult the current WCAG specification for the authoritative technical framing, associated guidelines, and success criteria (including their applicable conformance levels and the WCAG version in which each was introduced). This entry is informational and not legal advice.

Why it matters

"Understandable" is one of the four foundational principles of the Web Content Accessibility Guidelines (WCAG), and its ordinary meaning, capable of being readily understood, or intelligible, captures why it matters in digital contexts. If users cannot comprehend content or predict how an interface behaves, the content fails them regardless of whether it can technically be perceived or operated. Comprehension is a threshold requirement: information that reaches a user but cannot be understood does not serve its purpose.

The principle is especially significant because comprehension barriers affect a broad range of people, including those with cognitive, learning, or language-related disabilities, as well as users encountering content in a non-native language or under stressful circumstances. Interfaces that behave unpredictably, use unexplained jargon, or fail to guide users through errors can effectively exclude people even when other accessibility measures are in place.

Because the evidence supplied here supports only the ordinary-language meaning of the word, practitioners should treat the specialized WCAG framing, its associated guidelines, success criteria, conformance levels, and the WCAG version in which each criterion was introduced, as something to confirm against the current WCAG specification. This entry is informational and not legal advice; requirements and their interpretation evolve through regulation and case law, and qualified legal counsel should be consulted for compliance questions.

Who it's relevant to

UX designers and content authors

Those who write copy, label controls, and design interactions shape whether users can comprehend content and predict how an interface behaves. Clear, intelligible language and consistent, reasonable behavior directly support the Understandable principle.

Accessibility engineers and QA testers

Comprehension-related issues often cannot be caught by automated tools alone; automated testing detects only a portion of potential issues. Manual review and assistive technology testing are generally required to evaluate whether content and interface operation are genuinely understandable.

Compliance officers and legal counsel

The Understandable principle is one benchmark referenced when assessing WCAG conformance, but conformance is distinct from usability and from legal compliance. This entry is not legal advice, and the authoritative technical requirements should be confirmed against the current WCAG specification and relevant regulation or agency guidance.

Business leaders and product owners

Content that users cannot understand undermines the purpose of a product even when it is technically perceivable and operable. Prioritizing comprehension supports a broader range of users, including people with cognitive or language-related barriers, though it should not be treated as a guarantee of full compliance or legal immunity.

Inside Understandable

Understandable (POUR Principle)

One of the four foundational principles of the Web Content Accessibility Guidelines (WCAG), alongside Perceivable, Operable, and Robust. It broadly requires that information and the operation of a user interface be understandable to users.

Readable

A guideline under the Understandable principle addressing text readability, including making text content readable and identifying the language of the page and of specific passages so assistive technologies can present content correctly.

Predictable

A guideline under the Understandable principle intended to make web pages appear and operate in consistent, predictable ways, such as consistent navigation and consistent identification of components across a site.

Input Assistance

A guideline under the Understandable principle that helps users avoid and correct mistakes, including error identification, labels or instructions for input, and error suggestions where appropriate.

Conformance Levels

Success criteria supporting Understandable are distributed across the A, AA, and AAA levels. Level AA is the level most commonly cited as a target in accessibility programs and settlements, while AAA criteria are generally more stringent and not typically applied site-wide.

Common questions

Answers to the questions practitioners most commonly ask about Understandable.

Does meeting the Understandable principle mean my content is fully accessible and legally compliant?

No. Understandable is one of the four principles of WCAG (alongside Perceivable, Operable, and Robust), and satisfying its success criteria addresses only part of overall accessibility. Meeting WCAG success criteria does not guarantee an accessible experience for every user, nor does it guarantee immunity from legal claims. Automated testing detects only a portion of issues, so manual and assistive technology testing are generally needed. For questions about legal exposure, consult qualified legal counsel and current agency guidance, as requirements evolve through regulation and case law.

Is the Understandable principle a legal requirement mandated by the ADA?

The Understandable principle comes from WCAG, which is a set of technical guidelines published by the W3C through the Web Accessibility Initiative, not text codified within the ADA itself. The ADA is a US civil rights law and does not contain detailed web technical specifications. Courts, settlements, and some agency guidance have often referenced WCAG (commonly Level AA) as a benchmark, but you should attribute any specific obligation to the settlement, regulation, or guidance that established it rather than assuming the ADA directly mandates WCAG. This is general information, not legal advice.

What does the Understandable principle cover in practice?

Understandable generally addresses making both the information and the operation of the user interface comprehensible. In WCAG this principle is commonly associated with guidelines relating to readable content, predictable behavior of pages and components, and input assistance such as error identification and correction support. Because specific success criteria and their conformance levels differ across WCAG 2.0, 2.1, and 2.2, confirm the exact criteria and levels against the version you are targeting.

How can teams make content more readable under this principle?

Common approaches include identifying the language of the page and of individual passages so assistive technology can present content correctly, clarifying unusual words, abbreviations, or jargon where appropriate, and structuring content clearly. Note that some readability-related provisions in WCAG sit at higher conformance levels, so review which apply to your target level (AA is the level most commonly cited) rather than assuming all readability guidance is required.

What role does predictability play, and how do we support it?

Predictability generally means that components and pages behave in consistent, expected ways, for example, that changing a setting or focusing an element does not trigger an unexpected change of context without warning, and that navigation and repeated components appear consistently. Supporting this often involves consistent placement and labeling of recurring elements and avoiding automatic context changes that users did not initiate. Verify the exact success criteria and their levels against your target WCAG version.

How should we handle form errors to align with the input assistance guidance?

Practices commonly aligned with input assistance include clearly identifying when an error occurs, describing the error in text, providing labels or instructions for inputs, and, where relevant, offering suggestions to correct the error. Automated checks may catch some issues, but manual testing with assistive technology is generally needed to confirm that error messages are conveyed and usable. Because relevant success criteria span multiple WCAG versions and conformance levels, confirm which apply to the version and level you are targeting.

Common misconceptions

Making content Understandable is only about using simple or plain language.

While readability is one component, the Understandable principle also covers predictability of navigation and interface behavior and input assistance such as error identification and correction. Plain language addresses only part of the scope.

If a page passes automated accessibility checks, its content is fully understandable to all users.

Automated testing detects only a portion of potential issues. Many aspects of understandability, such as the clarity of instructions or the helpfulness of error suggestions, generally require manual review and testing with assistive technologies.

Meeting the Understandable success criteria guarantees legal compliance.

Conforming to WCAG success criteria is distinct from legal compliance and does not guarantee immunity from claims. US legal frameworks such as the ADA do not themselves codify detailed WCAG technical specifications, and requirements evolve through regulation and case law. Consult qualified legal counsel for specific obligations.

Best practices

Programmatically identify the default language of each page and the language of any distinct passages so assistive technologies present content accurately.

Provide clear labels and instructions for form fields, and ensure errors are identified in text and accompanied by suggestions for correction where appropriate.

Maintain consistent navigation and consistent identification of components across the site so users can predict where features are and how they behave.

Complement automated testing with manual review and testing using assistive technologies, since many understandability issues cannot be detected by automated tools alone.

Target Level AA success criteria as a commonly cited baseline, and evaluate applicable AAA criteria where feasible for higher assurance, recognizing AAA is generally not expected site-wide.

Treat WCAG conformance as separate from legal compliance and usability, and consult qualified legal counsel and current agency guidance for jurisdiction-specific obligations.