Q22 of 24 · Accessibility
How do you severity-rate and prioritise accessibility defects?
Short answer
Short answer: Severity should reflect user impact: Critical blocks a user entirely (no keyboard access, no alternative). High is a significant barrier with a workaround that's unreasonable. Medium has a workaround that's acceptable. Low is a minor announcement difference or non-critical contrast. Critical defects on public-facing flows should block release.
Detail
Accessibility defects are often rated on a four-level severity scale that maps to user impact, not WCAG level alone (though Level A failures are usually higher severity):
Critical: the user cannot complete the task at all. Examples: a modal with no keyboard close mechanism (keyboard trap), a form submit button with no accessible name (screen reader user cannot find or activate it), a page with no logical heading structure that a screen reader user must navigate by. Critical defects on core user journeys (sign-in, checkout, account management) should block release.
High: the user can complete the task but with significant difficulty or additional effort. Examples: form errors not announced by a screen reader (user must hunt to find what went wrong), insufficient contrast on important body text, focus order that's out of sequence but doesn't cause a trap. High defects should be in the next sprint's backlog.
Medium: a workaround exists and is reasonable. Examples: a missing skip navigation link (user must Tab through navigation on every page — inconvenient but possible), an icon's alt text that's technically present but not ideal. Medium defects go on the backlog.
Low: cosmetic or minor. Examples: a redundant ARIA label that duplicates the button text, a slightly wrong announcement order for a non-critical widget. Low defects are tracked but deprioritised.
Communicating priority to PMs: frame severity in terms of affected user population and legal risk — not WCAG clause numbers. "This blocks screen reader users from checking out, which is a legal risk under the ADA and affects approximately 2.5% of UK adults who use a screen reader" is a much more effective argument than "this violates WCAG 2.1 success criterion 1.3.1 Level A".