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Success criterion

A success criterion is one individual, testable requirement in - the numbered statements the whole standard is made of, such as 1.1.1 Non-text Content ("all non-text content has a text alternative") or 1.4.3 Contrast (Minimum) ("text has a contrast ratio of at least 4.5:1").

Each success criterion has:

  • A number and name - the number encodes where it sits in WCAG's structure (principle, guideline, criterion), and is how criteria are cited everywhere, including in Silktide's findings.
  • A - A, AA, or AAA - indicating how essential it is. Laws and regulations almost universally require Level AA, which includes everything in Level A.
  • A version it first appeared in - WCAG 2.1 and 2.2 each added new criteria on top of 2.0 without removing any, so "meets WCAG 2.1 AA" means satisfying every Level A and AA criterion present in version 2.1.

Success criteria describe outcomes, not implementations - 1.1.1 says images need a text alternative, not how to attach one in HTML or PDF. The per-technology "how" lives in techniques documents, and for PDFs the standard techniques are largely what specifies.

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