What Is WCAG? A, AA, and AAA Explained

WCAG — the Web Content Accessibility Guidelines — is the internationally recognised standard for making websites accessible to people with disabilities. Published by the W3C, it is organised around four principles (Perceivable, Operable, Understandable, Robust) and defines testable success criteria across three conformance levels: A, AA and AAA. In short: A is the bare minimum, AA is the level you should actually aim for and the one most laws require, and AAA is the highest bar, applied selectively rather than across a whole site. This guide explains how WCAG is structured and what those three levels really mean in practice.

It builds directly on what web accessibility is and why it matters, and feeds into the practical testing covered in how to check if a website is accessible.

What WCAG is and who maintains it

WCAG is produced by the World Wide Web Consortium (W3C) through its Web Accessibility Initiative (WAI). It is not a law in itself; it is a technical standard that laws, procurement rules and contracts around the world reference. That makes it the common language of accessibility — when a regulation, a client or a court says a site must be "accessible", they almost always mean "conforms to WCAG at a given level."

There are several versions in active use. WCAG 2.0 (2008) established the framework. WCAG 2.1 (2018) added criteria for mobile, low vision and cognitive needs. WCAG 2.2 (the most recent) adds further criteria — around focus visibility, dragging alternatives, consistent help and more. Crucially, the versions are additive: each new version keeps all the earlier success criteria and adds new ones, so conforming to 2.2 at a given level also satisfies 2.1 and 2.0 at that level. A future major revision (sometimes called WCAG 3.0) is in development but is not yet a finished, adoptable standard, so 2.2 AA is the sensible target today.

The structure: principles, guidelines, criteria

WCAG is a hierarchy with three layers, and understanding it makes the whole standard far less intimidating.

At the top are the four principles, captured by the acronym POUR:

• Perceivable — information and interface components must be presentable in ways users can perceive. They cannot use what they cannot perceive.
• Operable — interface components and navigation must be operable. Users must be able to drive the interface, whatever input they use.
• Understandable — information and the operation of the interface must be understandable. Content and behaviour should not confuse.
• Robust — content must be robust enough to be interpreted reliably by a wide variety of user agents, including assistive technologies — now and as technology evolves.

Beneath the principles sit guidelines — broad goals like "provide text alternatives" or "make all functionality available from a keyboard." And beneath each guideline sit the success criteria: specific, testable statements you can verify as pass or fail. The success criteria are where the real work is, and each one is assigned a conformance level of A, AA or AAA. So the chain runs: principle → guideline → success criterion (tagged A/AA/AAA).

The three conformance levels

The levels describe how strict a set of criteria you are meeting. They are cumulative: AA includes all of A, and AAA includes all of A and AA.

Level	What it means	Example criteria	Who it is for
A (minimum)	The most basic requirements; without these, some people cannot use the content at all	Non-text content has a text alternative; functionality is available from a keyboard; no content flashes more than three times per second; video has captions or an alternative for prerecorded media (varies by criterion)	The essential floor — barriers that completely block users must be removed first
AA (target)	A strong, usable experience for the great majority of users; the practical and legal standard	Colour contrast of at least 4.5:1 for normal text and 3:1 for large text; captions for prerecorded video; visible focus indicator; text resizes up to 200% without loss of content; consistent navigation	Most organisations and almost all accessibility laws — this is the level to commit to
AAA (enhanced)	The highest level; the best possible experience for the widest range of users	Contrast of at least 7:1 for normal text; sign-language interpretation for prerecorded audio; no time limits on most interactions; reading level and detailed help requirements	Specific audiences or content where the extra rigour is achievable and valuable; not a realistic site-wide goal

Level A: the floor

Level A criteria address barriers that, if unmet, make content unusable for some people entirely. Examples include providing a text alternative for non-text content (so a screen reader can describe an image), making all functionality available from a keyboard (so people who cannot use a mouse can still operate the site), and not using flashing content that could trigger seizures. Level A is necessary but not sufficient — a site can meet every Level A criterion and still be frustrating to use, which is why AA exists.

Level AA: the target

Level AA is the level you should aim for, full stop. It is the practical sweet spot between "minimally usable" and "perfect", and it is the level that accessibility laws effectively require — ADA-related case law, Section 508 and the European Accessibility Act all align with WCAG AA. Meeting AA means satisfying every Level A criterion plus the AA additions, which include some of the most impactful rules in the whole standard:

• Colour contrast of at least 4.5:1 for normal text and 3:1 for large text and UI components, so text is readable for people with low vision and in poor conditions.
• Captions for prerecorded video, so deaf and hard-of-hearing users get the audio content.
• A visible focus indicator, so keyboard users can always see where they are.
• Text resize up to 200% and reflow so content adapts to zoom and small screens without breaking.
• Consistent navigation and identification, so the interface is predictable.

If you only commit to one thing from this article, commit to WCAG 2.2 Level AA. It is the bar that makes a site genuinely accessible and legally defensible.

Level AAA: aspirational, applied selectively

Level AAA represents the gold standard — the best possible experience for the widest possible range of users. Its criteria are demanding: 7:1 contrast for normal text, sign-language interpretation for prerecorded audio, removal of nearly all time limits, lower reading levels, and extensive contextual help. The catch is that AAA is not achievable for all content across a whole site — the W3C itself states that AAA conformance is not possible to satisfy for some types of content. A news site cannot provide sign-language video for every clip; a technical reference cannot always lower its reading level without losing meaning. So AAA is not treated as a site-wide goal. Instead, mature teams adopt specific AAA criteria where they are achievable and add real value for their audience — for example, enhanced contrast for an interface used heavily by low-vision users.

How the levels map to POUR in practice

It helps to see how a single principle plays out across levels. Take Perceivable and the theme of contrast and media:

• A: prerecorded video has captions or an equivalent alternative (the specific requirement depends on the criterion), and non-text content has a text alternative.
• AA: text meets 4.5:1 contrast (3:1 for large text), and prerecorded video has captions.
• AAA: text meets the stricter 7:1 contrast, and prerecorded audio can include sign-language interpretation.

The same escalation pattern appears under Operable (from "keyboard accessible" at A, to a clearly visible focus indicator at AA, to enhanced focus appearance and the removal of timing constraints at AAA). Seeing this progression makes the levels intuitive: each level takes the same accessibility goal and demands more of it. We go deep on the operability side in how to make a website keyboard accessible, and on the perceivability side in how to write good alt text for images.

What conformance actually requires

A small but important detail: WCAG conformance is claimed at a level for a whole page (or set of pages), and to conform at a level you must meet all the success criteria at that level (and below). You cannot meet most AA criteria and call the page "AA" — partial conformance is not conformance. There are also conformance requirements about complete processes (a checkout flow must be accessible at every step) and about pages not undermining accessibility with conforming and non-conforming versions. The takeaway is that "AA" is a precise claim, not a vibe, which is why testing — covered next in this cluster — has to be systematic rather than a quick glance.

Common misunderstandings about WCAG

A few points trip teams up repeatedly. "WCAG is a law" — it is a standard that laws reference, not legislation itself. "AAA is the goal" — no; AA is the realistic, required target, and AAA is applied selectively. "Passing automated tools means I conform" — automated checkers verify only a fraction of success criteria; many criteria require human judgement, which is why how to check if a website is accessible stresses manual testing. "Newer WCAG versions replace older ones" — they are additive, so 2.2 includes everything in 2.1 and 2.0. Clearing up these points keeps a team aimed at the right target with the right method.

The bottom line

WCAG is the map for accessible web content: four POUR principles, broken into guidelines, broken into testable success criteria, each tagged A, AA or AAA. Level A removes total barriers, Level AA delivers a genuinely accessible experience and is what the law expects, and Level AAA is the enhanced ceiling you adopt in part rather than in full. Commit to WCAG 2.2 AA as your standard, understand that conformance means meeting every criterion at that level, and lean on real testing to verify it. From here, learn how to check if a website is accessible and what web accessibility is and why it matters for the bigger picture.

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