Or: The four things every accessible experience must do
Before we get into individual guidelines, there’s one mental model that underpins everything: POUR.
That’s not a typo. It’s an acronym – one you’re going to see a lot. POUR stands for:
- Perceivable
- Operable
- Understandable
- Robust
These are the four principles that the Web Content Accessibility Guidelines (WCAG) are built on. Every single success criterion maps back to one of them. That’s why it’s worth understanding them now – because they’ll show up over and over again.
And no, you don’t have to memorize them like commandments. But if you keep them in the back of your mind, they’ll start to shape how you think about accessibility in general.
Let’s break them down.
Perceivable
Can people sense the content – whether that’s through sight, sound, or touch?
If you’ve ever tried to watch a video without captions in a loud space or read light grey text on a white background, you know what it feels like to struggle with perceivability.
Good design makes sure content isn’t hidden behind color alone, that images have meaningful alt text, and that media works even when one sense is unavailable.
Operable
Can people use the interface?
This is about interaction. Buttons that are too small to tap. Slideshows that move too fast. Menus that disappear the second your mouse moves. These are all problems of operability.
Accessible experiences work whether you’re using a mouse, a keyboard, a switch device, or voice commands. They let users move through things at their own pace – and they don’t trap anyone along the way.
Understandable
Can people follow what’s going on?
You could have perfect contrast and beautiful markup, but if your form throws up a vague error like “Invalid input,” it’s still not accessible.
Understandable means your content, structure, and feedback make sense. It’s about clarity, consistency, and not surprising the user halfway through an action.
Robust
Does the thing hold up across tools and time?
The web is accessed by all kinds of devices and assistive technologies – screen readers, magnifiers, braille displays, voice control systems. If your site only works in Chrome on a Tuesday, that’s not robust.
This is the technical principle, but also the most future-focused. Clean, semantic code makes your site more likely to survive the next browser update or assistive tech evolution.
Together, these principles form the bedrock of accessibility. If something fails one of them, it probably fails all of them. But if you’re designing with POUR in mind, you’re already ahead of the game.
Don’t worry if it still feels abstract. These ideas will come to life as we walk through real examples in the rest of this guide.