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What Is WCAG? A Plain-Language Introduction

An accessible introduction to the Web Content Accessibility Guidelines (WCAG): what they are, the conformance levels, and the four POUR principles.

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The Web Content Accessibility Guidelines (WCAG) are the internationally recognized standard for making web content usable by people with disabilities. Published by the World Wide Web Consortium (W3C), they're the benchmark most teams use when they talk about an "accessible" website.

This article is informational and not legal advice.

The four principles (POUR)

WCAG organizes everything under four principles. Content must be:

  1. Perceivable — users can perceive the information (e.g. text alternatives for images, captions for video).
  2. Operable — users can operate the interface (e.g. everything works by keyboard, no keyboard traps).
  3. Understandable — content and operation are clear (e.g. predictable navigation, helpful error messages).
  4. Robust — content works across browsers and assistive technologies (e.g. valid, well-structured markup).

Conformance levels

WCAG defines three levels of conformance:

  • Level A — the most basic requirements.
  • Level AA — the level most organizations target; it covers the issues that affect the broadest range of users.
  • Level AAA — the strictest level, often impractical to meet site-wide.

When people refer to "WCAG 2.1 AA," they mean meeting all Level A and AA success criteria from version 2.1.

Common questions

Does WCAG apply to my website?

WCAG itself is a technical standard, not a law. But many laws, policies, and contracts around the world reference it as the measure of accessibility, so it's the practical target for most public-facing sites.

Can automated tools check WCAG for me?

Partly. Automated scanners reliably catch a subset of issues — missing alt text, low contrast, unlabeled fields — but many criteria require human judgment. Use automation to move fast, then verify key flows manually.

Where should I start?

Begin with the high-impact basics: text alternatives, color contrast, form labels, and keyboard operability. They cover a large share of real-world barriers.

Next steps

Read our fix guides for step-by-step walkthroughs of the most common issues, then scan your own site to see where you stand.