2.8 KiB
2.8 KiB
Severity Rubric
Core Principle
Severity = Impact x Likelihood, NOT WCAG conformance level.
- Level A vs AA is a conformance tier, not a risk rating
- A Level A failure can be LOW severity (decorative image missing alt)
- A Level AA failure can be CRITICAL (focus outline removed)
Severity Levels
Critical
- Description: Completely blocks access for users with disabilities
- Impact: Prevents task completion
- Examples:
- Keyboard trap preventing navigation (2.1.2, Level A)
- Missing alt text on primary action image (1.1.1, Level A)
- Form submission inaccessible via keyboard (2.1.1, Level A)
- Focus outline removed from focusable elements (2.4.7, Level AA)
High
- Description: Significantly degrades experience or blocks common workflows
- Impact: Makes tasks difficult or requires workarounds
- Examples:
- No skip navigation on complex site (2.4.1, Level A)
- Poor contrast on primary CTA button (1.4.3, Level AA)
- Missing error suggestions on required form (3.3.3, Level AA)
- Touch targets too small on mobile (2.5.8, Level AA)
Medium
- Description: Minor usability impact, affects subset of users
- Impact: Causes confusion or requires extra effort
- Examples:
- Decorative icon not hidden but in acceptable context (1.1.1, Level A)
- Link text needs slight improvement for clarity (2.4.4, Level A)
- Missing autocomplete on optional field (1.3.5, Level AA)
Low
- Description: Best practice enhancement, minimal user impact
- Impact: Nice-to-have improvement
- Examples:
- Could add tooltips for better UX (not required)
- Page title could be more descriptive (2.4.2, Level A - but functional)
Calculation Guide
Impact Assessment
| Level | Description | Severity Modifier |
|---|---|---|
| Blocker | Prevents access | Critical/High |
| Degraded | Makes difficult | High/Medium |
| Friction | Adds effort | Medium/Low |
| Minor | Barely noticeable | Low |
Likelihood Assessment
| Level | Description | Severity Modifier |
|---|---|---|
| Core flow | All users hit it | Increase severity |
| Common | Many users hit it | Base severity |
| Edge case | Few users hit it | Decrease severity |
| Rare | Almost never | Low |
Examples
Same Criterion, Different Severity
Missing alt text (1.1.1, Level A):
- Hero image: Impact=Blocker, Likelihood=All users → CRITICAL
- Decorative footer icon: Impact=Minor, Likelihood=Rare → LOW
No skip link (2.4.1, Level A):
- 3-item navigation: Impact=Friction, Likelihood=Common → MEDIUM
- 50-item navigation: Impact=Degraded, Likelihood=All users → HIGH
Poor contrast (1.4.3, Level AA):
- Primary CTA button: CRITICAL
- Body text: HIGH
- Footer link: MEDIUM
- Decorative text: LOW