Conciseness

The body is directive and does not explain concepts Claude already knows, but it is padded by repetition: the clarification-before-drafting rule appears in five places (Reference Module Integration, Clarification-First Rule, Decision Logic Step 1, Core Function, Hard Rules #1, Formatting Expectations), the Sections A–J list is duplicated in references/output-section-guidance.md, and the negative-scope list appears twice ("This skill must not confuse", "What This Skill Should Not Do"). This fits "mostly efficient but includes some unnecessary explanation or could be tightened"; it is not score-2 material since the prose itself is dense rules rather than filler explanation.

Actionability

As an instruction-only skill, the guidance is concrete: exact output sections A–J with per-section content, an exact operationalization-table column list, a copy-paste out-of-scope redirect template, and three named draft-status labels. It falls short of score 5 because there is no worked example of a finished endpoint definition or a filled-in operationalization table to anchor the output format; the examples given are input prompts, not outputs.

Workflow Clarity

Decision Logic Steps 1–8 are clearly sequenced, each mapped to a specific reference module, with an explicit validation checkpoint up front (Step 1 clarification gate), error-recovery feedback loops (Sections H and I identify weak endpoints and remaining clarifications, Section J gates the draft status), and a checklist-style Hard Rules section. This matches the score-5 anchor including its feedback-loop and checklist criteria; the score-4 anchor would imply missing checkpoints, which are present.

Progressive Disclosure

The Reference Module Integration section maps each of the 10 existing reference files to specific output sections, and the references are verified one level deep with no nested pointers, fitting "well-signaled one-level-deep references". However, the body partially inlines reference content — the A–J section list duplicates references/output-section-guidance.md and the eight-step body duplicates references/workflow-step-template.md — which keeps it at "good structure; minor organization gaps" rather than the score-5 anchor's appropriately split content.

Specificity

"Designs primary, secondary, and exploratory endpoints" plus "event rules, assessment timing, composite logic, interpretability, and protocol-stage auditability" names multiple concrete, specific actions with comprehensive coverage of the endpoint-design domain. It uses third-person voice ("Designs"), matching the top anchor rather than the score-4 anchor, which expects minor coverage gaps.

Completeness

The "what" is explicit (designs endpoint hierarchies, translates study aims into operational endpoint definitions) and the "when" is explicit: "Always use this skill when a user needs to translate study aims into operational endpoint definitions". Both are answered concretely, matching the score-5 anchor; the score-4 anchor would require a weaker or less explicit 'when' clause, which is not the case here.

Trigger Term Quality

Natural terms are present — "primary, secondary, and exploratory endpoints", "study aims", "endpoint definitions", "event rules", "assessment timing" — covering what a user would plausibly say. A few natural synonyms are missing (e.g., "outcome measures", "clinical trial", "protocol endpoints" as a standalone trigger), so it fits the "good keyword coverage; a few natural terms missing" anchor rather than the comprehensive score-5 example.

Distinctiveness Conflict Risk

"biomedical and clinical research protocols" with "rather than generic study design advice" carves out a clear niche with distinct triggers and minimal overlap risk with adjacent skills (e.g., general protocol-writing or statistics skills). It matches the "clear niche with distinct triggers" anchor, not the score-4 anchor that anticipates overlap with closely related skills.