Conciseness

The body is short and mostly tight, but the intro sentence explains a concept Claude already knows ("Navigation landmarks allow screen reader users to quickly jump to and identify different navigation areas—without them, users must tab through every link") and the Quick Reference bullets largely duplicate the Check and Fix sections ("Wrap navigation links in nav elements", "Use aria-label..." appear twice). This fits 'mostly efficient but includes some unnecessary explanation or could be tightened' rather than the minor-trim level of 4.

Actionability

As an instruction-only skill the guidance is concrete: "Verify navigation areas use nav elements with aria-label or aria-labelledby to distinguish primary, secondary, and footer navigation" and "descriptive aria-labels like 'Main navigation' or 'Footer navigation'" give specific elements, attributes, and example values. It is not 5 because the body contains no actual markup snippet — the code example is deferred entirely to references/rule.md, leaving a minor gap for the common cases.

Workflow Clarity

This is a simple single-task skill whose core action is unambiguous (check nav elements with distinguishing aria-labels in rendered markup), organized into Check/Fix/Explain/Code Review. However, "Provide skip links to bypass repetitive navigation" appears in Quick Reference yet is absent from both the Check and Fix sections, a minor coverage gap that keeps it below the fully unambiguous level of 5.

Progressive Disclosure

The body is a true overview and the full implementation details (code examples, framework guidance) live in references/rule.md, verified to exist, one level deep, and clearly signaled: "For full implementation details, code examples, and framework-specific guidance, see references/rule.md." This matches the 'clear overview with well-signaled one-level-deep references; content appropriately split' anchor exactly.

Specificity

The description names the domain ("Use navigation landmark regions") and one concrete action ("Validate the final browser-facing markup, not just the source framework abstraction"), but does not enumerate the actual capabilities such as checking nav elements, aria-labels, or skip links. It matches the 'names domain and 1-2 concrete actions, but not comprehensive' anchor rather than the 'several specific actions' anchor at 4.

Completeness

An explicit "Use when reviewing templates, rendered HTML, or shared components" clause answers 'when', and "Validate the final browser-facing markup" provides a 'what', but the actual task is garbled into "related to Use navigation landmark regions" rather than cleanly stated. It has both what and when with the 'when' explicit but the 'what' weakly conveyed — the anchor 4 fit, not the fully concrete anchor 5.

Trigger Term Quality

"templates, rendered HTML, or shared components" are reasonable developer triggers, but the most natural phrases a user would say for this need — "accessibility", "screen reader", "nav", "aria-label", "a11y" — are entirely absent. This matches the 'some relevant keywords but missing common variations or synonyms' anchor, below the 'good keyword coverage' anchor at 4.

Distinctiveness Conflict Risk

The navigation-landmark focus and rendered-markup scope give it a clear niche, though the boilerplate "Use when reviewing templates, rendered HTML, or shared components" prefix would also match sibling HTML/accessibility rule skills. This is 'mostly distinct; minor overlap risk with closely related skills', not the anchor 3 level of unresolved overlap, because the rule name explicitly distinguishes the trigger.