Web accessibility standard / WCAG 2.1 AA, criterion by criterion
WCAG 2.1 AA, criterion by criterion
WCAG (Web Content Accessibility Guidelines) is the technical standard the EU Accessibility Act, EN 301 549, and US ADA Title II all point to. It's organised around four principles — content must be Perceivable, Operable, Understandable, and Robust (POUR) — and three conformance levels, A, AA, and AAA, each stricter than the last.
Engine coverage today
20
AA criteria in scope
19
automated today
1
need manual review
EN 301 549 V3.2.1 (2021-03) / WCAG 2.1 AA
standard version
Sample report
WCAG 2.1 AAIllustrative example, not real scan data.
Perceivable
Information and interface components must be presentable to users in ways they can perceive — text alternatives, captions, sufficient contrast, adaptable layout.
Non-text content needs a text alternative
Images, icons, and other non-text elements that convey information must have a text alternative a screen reader can announce.
- WCAG
- 1.1.1
- EN 301 549
- 9.1.1.1
- Directive:
- Annex I, Section III(b)(vi)
Structure must be in the markup, not just the visuals
Headings, lists, tables, and form groupings that look structured visually must also be marked up correctly so assistive technology conveys the same structure.
- WCAG
- 1.3.1
- EN 301 549
- 9.1.3.1
- Directive:
- Annex I, Section III(c)
Common input fields should identify their purpose
Fields collecting common information (name, address, payment details) should use the correct `autocomplete` value so browsers and assistive technology can identify their purpose.
- WCAG
- 1.3.5
- EN 301 549
- 9.1.3.5
- Directive:
- Annex I, Section IV(g)(ii)
Don't use colour as the only signal
Information conveyed by colour alone (e.g. a link only distinguishable by its colour) is invisible to colour-blind users and anyone on a monochrome or high-contrast display.
- WCAG
- 1.4.1
- EN 301 549
- 9.1.4.1
- Directive:
- Annex I, Section III(c)
Auto-playing audio needs a way to stop it
Audio that plays automatically for more than 3 seconds must be pausable, stoppable, or have its volume independently controllable.
- WCAG
- 1.4.2
- EN 301 549
- 9.1.4.2
- Directive:
- Annex I, Section III(c)
Text needs enough contrast against its background
Normal text needs a contrast ratio of at least 4.5:1 against its background; large text (≥18.66px normal weight or ≥14px bold) needs at least 3:1.
- WCAG
- 1.4.3
- EN 301 549
- 9.1.4.3
- Directive:
- Annex I, Section III(b)(v)
Text must remain usable when zoomed to 200%
Zooming the page to 200% must not clip, overlap, or hide content — the layout should reflow.
- WCAG
- 1.4.4
- EN 301 549
- 9.1.4.4
- Directive:
- Annex I, Section III(b)(v)
Operable
Interface components and navigation must be operable, including by keyboard alone, with enough time and no content that triggers seizures.
Everything must work with a keyboard alone
All interactive functionality must be operable via keyboard, with no mouse-only interactions or keyboard traps.
- WCAG
- 2.1.1
- EN 301 549
- 9.2.1.1
- Directive:
- Annex I, Section III(c)
Time limits must be adjustable
Users must be able to turn off, adjust, or extend any time limit before it expires.
- WCAG
- 2.2.1
- EN 301 549
- 9.2.2.1
- Directive:
- Annex I, Section III(c)
Moving or blinking content needs a pause control
Auto-updating, scrolling, or blinking content lasting more than 5 seconds must be pausable, stoppable, or hideable.
- WCAG
- 2.2.2
- EN 301 549
- 9.2.2.2
- Directive:
- Annex I, Section III(c)
Provide a way to skip repeated navigation
Pages with repeated blocks of content (navigation menus, headers) need a mechanism to bypass them.
- WCAG
- 2.4.1
- EN 301 549
- 9.2.4.1
- Directive:
- Annex I, Section III(c)
Every page needs a descriptive title
Each page must have a non-empty `<title>` that describes its content or purpose.
- WCAG
- 2.4.2
- EN 301 549
- 9.2.4.2
- Directive:
- Annex I, Section III(c)
Links need meaningful text
A link's accessible name (its text, or context around it) must describe where it goes or what it does.
- WCAG
- 2.4.4
- EN 301 549
- 9.2.4.4
- Directive:
- Annex I, Section III(c)
Keyboard focus must be visible
Whichever element currently has keyboard focus must have a visible indicator (e.g. an outline).
- WCAG
- 2.4.7
- EN 301 549
- 9.2.4.7
- Directive:
- Annex I, Section III(c)
Understandable
Information and the operation of the interface must be understandable — readable text, predictable behaviour, help avoiding and correcting mistakes.
The page's language must be declared
The `<html>` element needs a valid `lang` attribute identifying the page's primary language.
- WCAG
- 3.1.1
- EN 301 549
- 9.3.1.1
- Directive:
- Annex I, Section III(c)
Language changes within a page must be marked
Passages in a different language from the surrounding content need a `lang` attribute with a valid language code.
- WCAG
- 3.1.2
- EN 301 549
- 9.3.1.2
- Directive:
- Annex I, Section III(c)
Form errors must be identified in text
When form validation fails, the specific error must be described in text, not conveyed by colour or an icon alone.
- WCAG
- 3.3.1
- EN 301 549
- 9.3.3.1
- Directive:
- Annex I, Section IV(g)(ii)
Form fields need labels or instructions
Every input needs a visible label or instruction describing what's expected, programmatically associated with the field.
- WCAG
- 3.3.2
- EN 301 549
- 9.3.3.2
- Directive:
- Annex I, Section IV(g)(ii)
Robust
Content must be robust enough to be interpreted reliably by current and future assistive technology, including screen readers.
Markup must be well-formed
HTML must be valid enough for assistive technology to parse reliably — most commonly, no duplicate `id` attributes.
- WCAG
- 4.1.1
- EN 301 549
- 9.4.1.1
- Directive:
- Annex I, Section III(c)
Interactive elements need a programmatic name, role, and state
Custom controls and ARIA widgets must expose a correct name, role, and state via markup so assistive technology can announce and operate them.
- WCAG
- 4.1.2
- EN 301 549
- 9.4.1.2
- Directive:
- Annex I, Section III(c)
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