Conciseness

The body is codebase-specific throughout (rate-limiter modes, env key convention, duplicate apiKey pattern) and assumes Claude's competence about general concepts, but has minor trimmable redundancy: the opening paragraph restates the frontmatter description, and the getCost example in Step 3 is repeated nearly verbatim under "Pricing: Prefer API-Reported Cost". This matches anchor 4 (efficient with minor over-explanation) rather than anchor 5 (every token earns its place).

Actionability

Every step ships concrete, executable TypeScript with exact file paths (`tools/types.ts`, `app/api/workspaces/[id]/byok-keys/route.ts`, `blocks/blocks/{service}.ts`), and the common cases are each covered with dedicated copy-paste-ready examples (API reports cost, API does not, async/polling capture, excluding operations via duplicate subblocks), plus named reference implementations (Exa, Google Maps). This matches anchor 5; anchor 4 would imply missing key details or non-runnable snippets, which are absent.

Workflow Clarity

The 6-step sequence is clearly ordered with an overview table, an explicit pre-code guard ("Before writing any getCost or rateLimit code, look up..."), an invariant ("getCost must always throw"), and a closing checklist — but there is no post-change verification step (typecheck/build/test) and no error-recovery loop for the author. That matches anchor 4 (clear sequence, most checkpoints, minor validation gaps) rather than anchor 5's full validate-fix-retry cycle. The operation is not destructive/batch, so the ≤3 cap does not apply.

Progressive Disclosure

No bundle files exist, so the skill is a single ~290-line file; it is well-sectioned with an overview table, numbered steps, and clear headings. Some self-contained content (the rate-limit research checklist, the duplicate-subblock pattern, and the Step 6 summary format example) would sit naturally in reference files, which is a minor organization gap matching anchor 4 rather than the well-split structure of anchor 5 or the buried/inlined-bulk problems of anchors 2-3.

Specificity

The description names a concrete primary action ("Add hosted API key support to a tool") plus specific mechanisms — "Sim provides the key when users don't bring their own", "BYOK support", "hideWhenHosted", "hosted key pricing" — giving several concrete capabilities with only minor coverage gaps (e.g., registration and UI steps are only implied). It lists several specific actions with minor gaps (anchor 4) rather than a comprehensive action list (anchor 5), and is well above the 1-2-action level of anchor 3.

Completeness

Both questions are explicitly answered: what — "Add hosted API key support to a tool so Sim provides the key when users don't bring their own"; when — "Use when adding hosted keys, BYOK support, hideWhenHosted, or hosted key pricing to a tool or block". This clearly matches anchor 5 (explicit what AND when with concrete trigger phrases); anchor 4 would require the 'when' to be less explicit or specific, which it is not.

Trigger Term Quality

Natural trigger phrases like "hosted keys", "BYOK support", "hosted key pricing", and the config field "hideWhenHosted" map directly to what a user would say when needing this skill. A few natural variants are missing (e.g., "bring your own key" spelled out, "API key", "metered"), which matches anchor 4 (good coverage, a few natural terms missing) rather than the comprehensive synonym coverage of anchor 5.

Distinctiveness Conflict Risk

The description occupies a clear niche — hosted key hosting mechanics specific to this platform (Sim, hideWhenHosted, BYOK) — with trigger terms unlikely to appear for unrelated skills, matching anchor 5 (clear niche with distinct triggers, minimal conflict risk). It is far more distinctive than anchor 4's "minor overlap risk with closely related skills".