Conciseness

The body is dense and operational — routing logic, safety tiers, exact flags, tag syntax — with essentially no explanation of concepts Claude already knows. However, there is minor duplication that could be trimmed: Global rule 5 ("Before responding to any matched sub-skill request, you MUST read references/{id}-instructions.md") restates step 2 of the Operating procedure, and the express-first default is stated in the intro, the decision matrix, and rule 6. Fits anchor 4 (efficient, minor over-explanation to trim) rather than 5 (every token earns its place) or 3 (noticeable unnecessary explanation).

Actionability

Guidance is fully executable within the body's scope: exact commands with resolved flags ("python3 scripts/acu_calculator.py estimate --instance <type> --cpu-p95 <val> ..."), exact CLI flags and anti-patterns ("create-db-cluster --with-express-configuration. Do NOT separately specify --engine-mode..."), copy-paste tag syntax, named IAM policy actions for AccessDenied, and scripted two-paragraph refusal templates. Matches anchor 5 (fully executable, copy-paste ready, common cases covered); anchor 4 would require missing key details, and the deliberate deferral of full create flows to the per-sub-skill instruction files is explicit and signaled, not a gap.

Workflow Clarity

The Operating procedure gives a clear 5-step ordered sequence with edge cases (multi-sub-skill requests, no match, failures), explicit validation checkpoints (confirmation before any mutation, tiered risk briefing before high-impact changes, "show the error and suggest a fix before retrying"), and a Troubleshooting section for error recovery — a validate→fix→retry feedback loop appropriate for database operations. Matches anchor 5 rather than 4, which would have missing checkpoints for risky operations.

Progressive Disclosure

The body is a clear router overview: a sub-skill registry table mapping intents to instruction files, with details split one level deep into 40 real reference files (all six references/{id}-instructions.md paths referenced in the body exist on disk) and three bundled scripts whose usage is given inline with deeper docs deferred to each script's --help. Navigation is easy and nothing that belongs in a reference is inlined. Matches anchor 5 (well-signaled one-level-deep references, appropriate split) rather than anchor 4, which would have organization gaps.

Specificity

Names the domain and several concrete actions — "creates, modifies, and advises on Aurora PostgreSQL clusters" — qualified by specific capabilities ("Aurora serverless, express configuration, pgvector, Babelfish"), but "advises" is somewhat generic and the action list is not comprehensive (e.g., no mention of cost analysis or upgrade execution as distinct actions). This matches anchor 4 (several specific actions, minor gaps) better than anchor 5, whose action coverage is exhaustive, and better than anchor 3, which covers only 1-2 actions.

Completeness

Explicitly answers both: what ("creates, modifies, and advises on Aurora PostgreSQL clusters") and when ("Trigger for Aurora PostgreSQL cluster operations, express-configuration quick-start, ACU sizing, I/O-Optimized storage, commitment pricing, or PostgreSQL upgrade planning"). This matches anchor 5 — clear 'what' plus explicit 'when' with concrete trigger phrases — and exceeds anchor 4, where the 'when' is only loosely specified.

Trigger Term Quality

"Aurora PostgreSQL cluster operations, express-configuration quick-start, ACU sizing, I/O-Optimized storage, commitment pricing, or PostgreSQL upgrade planning" are natural phrases users would say, but common variations like "Reserved Instance", "Savings Plan", "serverless", or "scale to zero" are absent. Fits anchor 4 (good keyword coverage, a few natural terms missing) rather than 5 (comprehensive synonyms) or 3 (missing common variations broadly).

Distinctiveness Conflict Risk

A clear niche ("Aurora PostgreSQL clusters specifically") with an explicit disambiguation — "For Aurora MySQL, use amazon-aurora-mysql instead" — minimizing conflict risk with the sibling skill. Matches anchor 5 (clear niche, distinct triggers, minimal conflict) rather than anchor 4, which would leave overlap risk with closely related skills.