Conciseness

The body is lean, assumes Claude's competence, and explains nothing Claude already knows; every section adds operational facts (routes, fields, output shape). It falls short of the anchor-5 "every token earns its place" because the route guidance is stated twice — "Prefer the documented public routes ... Start with `es_search/` ... use `compound/<CHEBI:id>/`" in Operating rules and again nearly verbatim as "Prefer these paths: `chebi/backend/api/public/es_search/`, ... `compound/<CHEBI:id>/`, and ontology child or parent routes" in Execution behavior — which could be merged into one mention.

Actionability

The Execution section gives a fully executable, copy-paste-ready command (`echo '{...}' | python scripts/rest_request.py`), the Input section adds three additional concrete JSON request patterns covering the common cases (free-text search, targeted compound fetch, ontology children), and the documented fields all match the actual `scripts/rest_request.py` interface. This matches anchor 5 ("fully executable; copy-paste ready code or commands; specific examples cover the common cases") and exceeds anchor 4, which allows minor gaps.

Workflow Clarity

This is a simple, single-purpose skill (make one API request) whose single action is unambiguous: build the documented JSON payload, pipe it to `scripts/rest_request.py`. The routing decision is explicit ("Start with `es_search/` for free-text lookup and use `compound/<CHEBI:id>/` for targeted records") and failure feedback is specified ("Failure returns `ok=false` with `error.code` and `error.message`"). No destructive or batch operations exist, so the validation cap does not apply, and the simple-skill exception makes this a 5.

Progressive Disclosure

The skill is under 50 lines with no need for external reference files: the References section explicitly states "No additional runtime references are required; keep the import package limited to this file and `scripts/rest_request.py`", and that script exists in the bundle and is correctly referenced. Per the guideline that under-50-line skills with no external-reference need score 5 with well-organized sections, the clean sectioning (Operating rules, Execution behavior, Input, Output, Execution, References) qualifies.

Specificity

The description names the domain and four concrete capability areas — "chemical search, compound lookup, ontology traversal, and structure metadata" — which matches the anchor "lists several specific actions; minor gaps in coverage". It falls short of a 5 because the actions are framed generically as things it "submit[s] compact ... API requests for" rather than stating the distinct concrete outcomes of each action, and coverage of the API's capabilities is not comprehensive.

Completeness

It explicitly answers both: the 'what' is "Submit compact ChEBI 2.0 API requests for chemical search, compound lookup, ontology traversal, and structure metadata" and the 'when' is "Use when a user wants concise ChEBI summaries". It is not a 5 because the 'when' clause is noticeably narrower than the 'what' — it only mentions wanting concise summaries, not searching compounds, traversing the ontology, or fetching structure metadata — so the trigger guidance could be more explicit and specific.

Trigger Term Quality

It includes some relevant natural terms ("chemical search", "compound lookup", "ChEBI", "ontology") but misses common variations and synonyms a user would naturally say — e.g. "look up a molecule", "chemical entity", "compound information", "mass/charge search". The single trigger phrase "when a user wants concise ChEBI summaries" also narrows discoverability to users who already know the ChEBI name, which fits anchor 3 ("some relevant keywords but missing common variations or synonyms") rather than the good-coverage anchor 4.

Distinctiveness Conflict Risk

"ChEBI 2.0 API" plus the named chemical-ontology capabilities define a clear niche with distinct triggers and virtually no overlap risk with other skills; nothing in the description is generic enough to fire for the wrong skill. It matches the anchor-5 example's profile (clear niche with distinct triggers) and is clearly not a 4, which requires actual minor overlap with closely related skills.