Conciseness

The body is dense with material Claude does not know (signal-phrase table, threshold/measurement/scope test, rewrite examples, output template, anti-patterns), with only minor over-explanation — the verbatim ISTQB glossary quote and the ISO 25010 framing rows ("(developer-facing)", "(out)") could be trimmed. Not 5: the Overview quotes a definition of non-functional testing Claude already knows; not 3: the padding is minor relative to the actionable bulk.

Actionability

Concrete, executable guidance throughout: per-family signal phrases, the three-part testability test, five specific rewrites with real tools and thresholds ("p95 page-load time on /dashboard is ≤2.5s, measured by Lighthouse CI under 4G throttling"), load-bearing Web Vitals defaults (LCP ≤2.5s, INP ≤200ms, CLS ≤0.1), and a copy-paste output template. As an instruction-only skill with fully actionable guidance, absence of code is not penalized; not 4: the worked example plus template cover the common cases completely.

Workflow Clarity

"How to use" lays out a clear 6-step sequence, step 6 plus the "Threshold gaps (HUMAN INPUT REQUIRED)" list is an explicit human-confirmation checkpoint, and the two-pass worked example demonstrates the error-recovery feedback loop (vague input → gap questions → author returns thresholds → final tables). The "never fabricates a threshold" rule guards the key failure mode; not 4: checkpoints and the feedback loop are explicit rather than implicit.

Progressive Disclosure

The single bundle file, references/measurement-sources.md, exists, holds the per-family measurement catalog, and is linked twice with clear markdown links at exactly the points it is needed (How-to-use step 5 and Step 3), exactly one level deep. The catalog is appropriately split out while the workflow content stays in SKILL.md; not 4: the reference is well signaled and navigation is easy with no organization gaps.

Specificity

"Extracts performance, accessibility, security, i18n, reliability and observability needs as threshold-bound assertions, each mapped to its measurement source (Lighthouse, axe, OWASP ASVS, WCAG)" lists multiple concrete actions with named tooling and covers all six of the skill's NFR families comprehensively. Not 4: coverage is exhaustive across the domain, with no gaps in the actions named.

Completeness

Explicitly answers "what" ("Extracts performance, accessibility, security, i18n, reliability and observability needs as threshold-bound assertions") and "when" ("Use when a PRD, design doc or product brief must be turned into testable non-functional requirements") with concrete trigger phrases. Not 4: the when-clause is specific and trigger-laden, not merely present.

Trigger Term Quality

"PRD, design doc or product brief" and "testable non-functional requirements" are natural phrases users would say when needing this skill, but common synonyms like "NFRs", "quality attributes", or "-ilities" are absent. Not 5: a few natural trigger variations are missing; not 3: the terms present are relevant and natural rather than partially covered.

Distinctiveness Conflict Risk

The niche is clear — turning docs into threshold-bound non-functional requirements with named standards (Lighthouse, axe, OWASP ASVS, WCAG) — and the trigger phrase "non-functional requirements" itself distinguishes it from functional/BDD or general document skills. Not 4: the "Use when" gate is specific enough that overlap with related skills is minimal.