Conciseness

Every line carries API-specific facts Claude could not know (entitlement gating, X-WorldMonitor-Key header, M49 code shapes, basis semantics, nonAdValoremLines averaging caveats, the closed unavailableReason enum) with zero padding and no explanation of concepts Claude already knows — matching the lean anchor-5 case.

Actionability

A copy-paste-ready curl with the auth header, URL-encoded parameters, and a jq projection; the exact endpoint URL; a parameter table with concrete value shapes; a complete response example; and explicit error codes with retry guidance — matches the fully-executable anchor-5 example.

Workflow Clarity

A simple skill whose single action is unambiguous (authenticate, call, interpret, report), with an explicit validation checkpoint ("Read `basis` before quoting `appliedRate`") and genuine feedback loops: retry with an explicit earlier year when MFN_PREFERENCES_NOT_REPORTED, check group membership before relying on a group preference, and 429 backoff — meeting the simple-skill exception plus anchor-5 recovery guidance.

Progressive Disclosure

The single SKILL.md is well-sectioned (Authentication, Endpoint, Parameters, Response shape, Worked example, Errors) with all content appropriately placed for a single-endpoint skill and no bundle files to organize. It sits just above the under-50-line simple-skill threshold as a flat ~95-line API doc with no reference split, matching anchor 4 (good structure, appropriately placed, minor organization gaps) rather than anchor 5's exemplary overview-plus-signaled-references pattern.

Specificity

"Look up the applied tariff on one HS6 product imported by one country from another (MFN, partner-specific preferential, and the best available applied rate), from UNCTAD TRAINS via World Bank WITS" names concrete actions, enumerates all rate variants, and cites the data source — comprehensive coverage for the domain, matching the anchor-5 example pattern rather than the minor-gaps anchor 4.

Completeness

It explicitly answers both: what it does ("Look up the applied tariff... MFN, partner-specific preferential, and the best available applied rate") and when to use it ("Use when the user asks what duty a specific product pays between two specific countries"), mirroring the anchor-5 example structure; it is not the anchor-4 case since the 'when' clause is fully explicit.

Trigger Term Quality

Natural terms like "tariff", "duty", "imported", and "what duty a specific product pays between two specific countries" match how users phrase the request, but common synonyms such as "import duty", "customs duty", or "trade agreement" are absent — good coverage with a few natural terms missing, not the comprehensive synonym coverage of anchor 5.

Distinctiveness Conflict Risk

A clear niche (bilateral HS6 tariff lookup via UNCTAD TRAINS/WITS) with distinct triggers, but a US-importer query could plausibly trigger both this skill and the sibling lookup-us-import-duty skill referenced in the body — minor overlap risk with a closely related skill, matching anchor 4 rather than the minimal-conflict anchor 5.