Conciseness

The body is lean (~30 lines) with well-earned Quick Reference bullets ("Avoid using 'yes/no' where 'true/false' is required"), matching 'efficient; minor instances of over-explanation that could be trimmed'. It is not 5 because the opening line ("Invalid attribute values cause ARIA properties to be ignored or misinterpreted...") explains a concept Claude already knows, and the one-line Check/Fix sections partially duplicate content one click away in references/rule.md. It is well above 3 — there is no padding or library-tour verbosity.

Actionability

The Quick Reference gives some concrete guidance ("aria-expanded=\"true\"", "Avoid using 'yes/no' where 'true/false' is required", "Check that IDs referenced in aria-labelledby or aria-owns actually exist"), but the Check and Fix sections are abstract direction — "Validate that all ARIA attribute values conform to the allowed types" and "Correct any invalid ARIA attribute values to match the expected format" — with no tool, command, or code example in the body itself (the ✅/❌ HTML examples live only in references/rule.md). This matches 'some concrete guidance but incomplete; missing key details' rather than 4, which requires concrete code or commands in the body.

Workflow Clarity

The Check → Fix → Explain → Code Review sections sequence the task clearly, and the Code Review section includes a verification checkpoint ("note how to verify the fix with browser accessibility tooling or assistive tech"), matching 'clear sequence with most checkpoints present; minor validation gaps'. It is not 5 because the body never says how to validate (the axe/Lighthouse/accessibility-tree steps sit in rule.md) and the verification checkpoint is a mention, not an explicit loop; it is above 3 because sequence and a validation mention are both present, and this simple review task involves no destructive or batch operations that would cap the score.

Progressive Disclosure

The bundle matches the ideal structure: a short overview body with a clearly signaled one-level-deep reference — "For full implementation details, code examples, and framework-specific guidance, see references/rule.md" — and references/rule.md exists, contains the detailed code examples/exceptions/verification, and itself references no further files. Content is appropriately split between overview and detail with easy navigation; the only trivial redundancy is the trailing 'Rule page:' URL line.

Specificity

The description lists several concrete actions — "Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output" — matching the anchor 'lists several specific actions; minor gaps in coverage'. It is not a 5 because the core rule-specific action (validating ARIA attribute values against allowed types such as boolean/integer/ID list) is never stated as an action; not a 3 because it goes well beyond '1-2 concrete actions' with five distinct review steps.

Completeness

Both 'what' and 'when' are explicitly present: the when clause is "Use when reviewing rendered HTML, interactive components, or design-system patterns..." and the what is "Check native semantics first, then inspect keyboard behavior, focus flow, accessible names, and screen-reader output". It matches the 4 anchor ('both present; when could be more explicit') rather than 5 because the templated phrase "related to Use valid values for ARIA attributes" is awkward and the stated what describes a generic accessibility review rather than the skill's actual task of validating ARIA attribute values.

Trigger Term Quality

Good natural keyword coverage: "reviewing rendered HTML", "interactive components", "design-system patterns", "ARIA attributes", "keyboard behavior", "focus flow", "screen-reader output" — phrases users would plausibly say. It falls short of the 5 anchor ('comprehensive coverage including synonyms') because common variations like "accessibility", "a11y", or specific attribute names (e.g., aria-expanded) are missing; it is above 3 because the terms present are domain-natural, not generic.

Distinctiveness Conflict Risk

The trigger set "reviewing rendered HTML, interactive components, or design-system patterns" plus "Check native semantics first, then inspect keyboard behavior..." is a generic accessibility-review preamble that would be nearly identical across sibling ARIA rules (aria-roles, aria-prohibited-attr, etc.), so it 'could still overlap with similar skills' (anchor 3). It is not 4 because only the embedded rule title distinguishes it from closely related skills; it is above 2 because the ARIA rule title does carve out a recognizable niche.