CONCEPT Cited by 1 source

WCAG 2.1 A / AA scope

Definition

WCAG 2.1 Levels A and AA is the conventional scope-picker for automated accessibility checks at organisations that take a11y seriously but haven't opted into AAA compliance. WCAG (Web Content Accessibility Guidelines) is the W3C's accessibility standard; version 2.1 was published 2018. Each guideline has success criteria marked at three levels:

• A — minimum, must-pass for basic accessibility (things like alt text on images).
• AA — the industry-standard target; covers colour contrast, keyboard navigation, form labels, language identification.
• AAA — enhanced (extreme contrast, sign-language alternatives). Rarely adopted wholesale because some criteria are impossible on certain content types.

Expression in automated tooling

In Axe Core the scope is selected via the tag set on the builder:

new AxeBuilder({ page })
  .withTags(['wcag2a', 'wcag2aa', 'wcag21a', 'wcag21aa'])
  .analyze();

The four tags:

• wcag2a — WCAG 2.0 Level A
• wcag2aa — WCAG 2.0 Level AA
• wcag21a — WCAG 2.1 Level A (adds rules over 2.0)
• wcag21aa — WCAG 2.1 Level AA (adds rules over 2.0 AA)

Including all four gives the full WCAG 2.1 A+AA rule set. Axe also ships wcag22aa (WCAG 2.2), best-practice (Axe's judgment calls not tied to a specific criterion), and EN-301-549 (European public-sector procurement standard) / ACT (W3C Accessibility Conformance Testing rules) as complementary tag sets.

Why this scope

• AA is the regulatory default. US Section 508, EU EN 301 549, many country-specific web-accessibility laws reference WCAG 2.x AA as the bar.
• Automated testing can cover A and AA rules. Axe's rule set maps to specific success criteria; most A and AA criteria that are machine-checkable have Axe rules.
• AAA is not universally applicable. Some AAA criteria are inherently content-type-specific (sign-language interpretation for video, 7:1 contrast ratio) and aren't useful as a blanket gate.
• Complementary with manual testing. WCAG includes criteria that can't be automatically checked (e.g., meaningful alt text, correct heading structure for the actual content) — see concepts/automated-vs-manual-testing-complementarity.

Seen in

• sources/2025-01-07-slack-automated-accessibility-testing-at-slack — Slack explicitly set its Axe scope to WCAG 2.1 A + AA via the four-tag set: "We wanted to check for compliance with WCAG 2.1, Levels A and AA."

Related

• systems/axe-core — the rule engine whose tag set expresses this scope.
• systems/axe-core-playwright — the binding exposing .withTags([...]).
• concepts/severity-filtered-violation-reporting — the orthogonal axis of filtering by impact severity.
• concepts/automated-vs-manual-testing-complementarity — why WCAG-AA-automated is a layer, not the whole strategy.