What does POUR stand for?

POUR is the acronym for the four guiding principles of the W3C Web Content Accessibility Guidelines: Perceivable, Operable, Understandable, and Robust. Every WCAG success criterion is organized under one of these four principles.

What is an example of "Perceivable"?

Adding alt text to an image makes it perceivable to a screen reader user. Providing captions for a video makes it perceivable to a Deaf user. Ensuring 4.5:1 color contrast (WCAG 1.4.3) makes text perceivable to a low-vision user.

What is an example of "Operable"?

Making every interactive control reachable and usable with the keyboard alone (WCAG 2.1.1) is the most common Operable requirement. Other examples: visible focus indicators (2.4.7), skip-to-content links (2.4.1), and avoiding seizure-triggering flash (2.3.1).

What is an example of "Understandable"?

Setting the page language with the html lang attribute (WCAG 3.1.1) is the canonical Understandable example. Others: consistent navigation across pages (3.2.3), clear error identification (3.3.1), and predictable focus behavior (3.2.1).

What is an example of "Robust"?

Robust means content works with current and future user agents — especially assistive technology. The flagship Robust criterion is 4.1.2 Name, Role, Value: every UI component must expose its name, role, and state to assistive tech. Using ARIA correctly (rather than reinventing semantics) is the canonical Robust practice.

POUR: Perceivable, Operable, Understandable, Robust

POUR is the organizing framework of the W3C Web Content Accessibility Guidelines. Every one of the 78 WCAG 2.1 success criteria sits under one of four principles — Perceivable, Operable, Understandable, and Robust. The framework was introduced in WCAG 2.0 (2008) and is preserved in WCAG 2.1 (2018) and WCAG 2.2 (October 2023).

PPerceivable

Information and UI components must be presentable to users in ways they can perceive. They cannot be invisible to all of a user's senses.

Example criteria:

Alt text on meaningful images (WCAG 1.1.1)
Captions on prerecorded video (1.2.2)
Color contrast of at least 4.5:1 for body text (1.4.3)
Resizable text up to 200% (1.4.4)
No reliance on color alone to convey meaning (1.4.1)

What failure looks like: Per WebAIM Million 2026, the top two perceivable failures are low contrast text (83.9% of home pages) and missing alt text (53.1%).

OOperable

UI components and navigation must be operable. Users must be able to operate the interface — interface cannot require interaction a user cannot perform.

Example criteria:

Keyboard accessibility for every interactive control (2.1.1)
No keyboard traps (2.1.2)
Visible focus indicators (2.4.7)
Skip-to-content links (2.4.1)
No content flashes more than 3 times per second (2.3.1)
Target size for pointer inputs at least 24x24 px (WCAG 2.2: 2.5.8)

What failure looks like: Empty links (46.3%) and empty buttons (30.6%) are the most prevalent operable failures — users see something clickable but assistive tech reads nothing.

UUnderstandable

Information and operation of the UI must be understandable. Content must be readable and predictable; users must be helped to avoid and correct mistakes.

Example criteria:

html lang attribute (3.1.1)
Foreign-language passages marked with lang (3.1.2)
Consistent navigation across pages (3.2.3)
Error identification in text, not only color (3.3.1)
Labels and instructions for inputs (3.3.2)
No cognitive function tests for authentication (WCAG 2.2: 3.3.8)

What failure looks like: Missing form input labels (51% of home pages) is the most prevalent understandable failure.

RRobust

Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies.

Example criteria:

Name, Role, Value exposed on every UI component (4.1.2)
ARIA used correctly — and only where native HTML cannot express semantics
Valid HTML parsing (historically 4.1.1, retired in WCAG 2.2)
Status messages exposed via role="status", role="alert", aria-live (4.1.3)

What failure looks like: Per WebAIM, ARIA usage is up 27% YoY and 6x since 2019 — but pages with ARIA average MORE errors than pages without. ARIA is a last resort, not a fix for poor HTML.

Ready to map this to your site? Open the 50-item ADA compliance checklist — items are tagged with the WCAG criterion and the POUR principle they sit under.

FAQ

What does POUR stand for?: POUR is the acronym for the four guiding principles of the W3C Web Content Accessibility Guidelines: Perceivable, Operable, Understandable, and Robust. Every WCAG success criterion is organized under one of these four principles.
What is an example of "Perceivable"?: Adding alt text to an image makes it perceivable to a screen reader user. Providing captions for a video makes it perceivable to a Deaf user. Ensuring 4.5:1 color contrast (WCAG 1.4.3) makes text perceivable to a low-vision user.
What is an example of "Operable"?: Making every interactive control reachable and usable with the keyboard alone (WCAG 2.1.1) is the most common Operable requirement. Other examples: visible focus indicators (2.4.7), skip-to-content links (2.4.1), and avoiding seizure-triggering flash (2.3.1).
What is an example of "Understandable"?: Setting the page language with the html lang attribute (WCAG 3.1.1) is the canonical Understandable example. Others: consistent navigation across pages (3.2.3), clear error identification (3.3.1), and predictable focus behavior (3.2.1).
What is an example of "Robust"?: Robust means content works with current and future user agents — especially assistive technology. The flagship Robust criterion is 4.1.2 Name, Role, Value: every UI component must expose its name, role, and state to assistive tech. Using ARIA correctly (rather than reinventing semantics) is the canonical Robust practice.