POUR Principles

POUR is the mnemonic for the four principles that organize the entire Web Content Accessibility Guidelines. Every WCAG guideline and success criterion sits under one of these four principles, so POUR is a useful mental model for understanding why any given requirement exists. The four principles are Perceivable, Operable, Understandable, and Robust.

The four principles

• Perceivable — information and interface components must be presentable to users in ways they can perceive. This covers text alternatives for images, captions and transcripts for media, sufficient color contrast, and content that does not rely on a single sense such as color alone.
• Operable — user interface components and navigation must be operable. Everything must work by keyboard, users must have enough time to read and interact, content must not be designed in ways known to cause seizures, and people must be able to find their way and know where they are.
• Understandable — information and the operation of the interface must be understandable. Text should be readable, pages should behave in predictable ways, and forms should help users avoid and correct mistakes.
• Robust — content must be robust enough to be interpreted reliably by a wide variety of user agents, including assistive technologies. In practice this means using valid, well-structured markup and correct name, role, and value information so that screen readers and other tools can parse the page.

The value of POUR is diagnostic. When you encounter an accessibility failure, mapping it back to a principle clarifies the underlying problem: a missing caption is a Perceivable failure, a mouse-only control is an Operable failure, an unlabeled error message is an Understandable failure, and a custom widget with no exposed role is a Robust failure. Framing issues this way keeps remediation focused on user impact rather than on checklist mechanics.