Conciseness

The body is lean throughout: no concept explanations, no library comparisons, and compact numbered question lists ('What's the MVP? (smallest thing that proves the thesis)'). Every line carries guidance, including the framing asides ('Like YC office hours but automated'), so there is nothing over-explained to trim as a 4 would require.

Actionability

Instruction-only guidance is concrete and executable: exact questions with quantification hints, exact inputs ('Read README, CLAUDE.md, package.json, recent commits'), an exact scoring formula ('impact (1-5) × confidence (1-5) ÷ effort (1-5)'), and a defined artifact ('a `PRODUCT-BRIEF.md`'). Not a 5: a few steps are underspecified — Mode 3's 'Compare to competitor onboarding' gives no method, and the 0-10 founder-review signal scoring lacks defined anchors.

Workflow Clarity

Each of the four modes has a numbered, ordered procedure with a defined output, and Mode 1 specifies the follow-on handoff ('the next lane is product-capability'). Not a 5: validation checkpoints are absent — no step to confirm the brief's answers with the user or to re-ask unanswered diagnostic questions; no destructive/batch operations exist, so the score-3 cap does not apply.

Progressive Disclosure

The body is cleanly sectioned (When to Use, four mode subsections, Output, Integration), fully self-contained with no bundle files, and its cross-skill mentions are handoffs rather than dangling references. Not a 5: at roughly 80 body lines it exceeds the under-50-line simple-skill bar, and growing detail such as the founder-review scoring rubric would belong in a one-level-deep reference file.

Specificity

The description lists four specific capabilities with concrete artifacts and mechanisms ('a YC-style product diagnostic that produces PRODUCT-BRIEF.md with a go/no-go recommendation, a founder review scoring product-market-fit signals, a user journey audit measuring time-to-value, and ICE feature prioritization'). It is not a 5 because the lead phrase 'Validate the why before building' is abstract framing and modes 2-4 lack their output artifacts; it is well above a 3 because multiple concrete actions are comprehensively enumerated rather than just 1-2.

Completeness

It explicitly answers both what (the four enumerated diagnostics with named outputs and scoring approaches) and when (a dedicated 'Use when...' clause with four concrete trigger scenarios), mirroring the anchor-5 example structure. Not a 4: the 'when' guidance is explicit and specific rather than merely present.

Trigger Term Quality

'Use when pressure-testing product direction, choosing between features, sanity-checking a launch, or converting a vague idea into a product brief' captures natural user phrasing across the skill's use cases. It falls short of a 5 because common synonyms such as 'prioritize features', 'product-market fit', or 'go/no-go decision' are missing.

Distinctiveness Conflict Risk

The product-diagnostic framing ('pressure-testing product direction', 'go/no-go recommendation', 'ICE feature prioritization') carves a clear niche distinct from generic planning skills. Not a 5: 'sanity-checking a launch' and 'choosing between features' have some overlap risk with roadmap/brainstorming-type skills.