Conciseness

The ~25-line body is lean and assumes Claude's competence: terse imperatives like 'Strong typography, gentle gradients, accessible contrast' and a compact per-phone element list, with zero explanation of concepts Claude already knows. Every token earns its place, matching the top anchor.

Actionability

The workflow gives concrete structural guidance (status bar, hero, headline, 3-dot pagination, full-width pill CTA) and an explicit output contract with a copy-paste artifact tag, but key details are missing and the first step — 'Read DESIGN.md' — points to a file that does not exist in the bundle, making it unexecutable as written. This fits the anchor for concrete-but-incomplete guidance with missing key details rather than the mostly-executable level above.

Workflow Clarity

Steps 1–5 are sequenced coherently (read brief, identify audience, lay out three phones, make the last phone sign-in, apply styling), matching 'steps listed but checkpoints missing or implicit'. It cannot reach 4–5 because step 1 references a nonexistent file and there is no verification or review checkpoint anywhere (e.g., a contrast/QA check before emitting the artifact), while step 5 is a style directive rather than a process step.

Progressive Disclosure

The skill is under 50 lines with no bundle files and clean section organization ('## Workflow', '## Output contract'), which would ordinarily merit a 5 under the simple-skill exception. It drops to 4 because the body's only reference — 'Read DESIGN.md' — is dangling, so navigation to supporting material is broken rather than clearly signaled.

Specificity

The description lists several concrete deliverable elements — 'three phone frames side by side', 'Status bar, swipe dots, primary CTA', 'splash, value-prop, sign-in' — which matches the anchor for several specific actions with minor gaps. It stops short of a 5 because the action side is thin: 'A multi-screen mobile onboarding flow rendered' is the only verb phrase, and it doesn't state what is produced beyond the artifact layout.

Completeness

Both questions are answered explicitly: the 'what' is concrete ('A multi-screen mobile onboarding flow rendered as three phone frames side by side — splash, value-prop, sign-in') and the 'when' is an explicit trigger clause with concrete phrases ('Use when the brief mentions "mobile onboarding", "iOS onboarding", "phone signup", or "移动端引导"'). This matches the top anchor exactly.

Trigger Term Quality

Natural phrases a user would say are present ('"mobile onboarding"', '"iOS onboarding"', '"phone signup"', '"移动端引导"'), giving good keyword coverage. Not a 5 because common variations are missing from the description itself — e.g. 'android onboarding' and 'app onboarding' appear in the frontmatter triggers list but not in the description text.

Distinctiveness Conflict Risk

It carves a clear niche — a three-screen mobile onboarding design prototype — with distinct, specific triggers ('mobile onboarding', 'phone signup', '移动端引导') unlikely to collide with other skills. Nothing generic remains that would overlap with broader design or document skills.