Conciseness

The body is mostly lean — SQL snippets, a symptom/remedy table, and checklists — but the 'Senior database optimizer with expertise...' role preamble and the 'When to Use This Skill' bullet list substantially duplicate the description's content, tokens that could be trimmed. Not 3: there is no re-teaching of concepts Claude already knows and no padded explanation.

Actionability

Fully executable, copy-paste-ready SQL covering the common cases: pg_stat_statements top-query listing, EXPLAIN (ANALYZE, BUFFERS) plan capture, CREATE INDEX CONCURRENTLY ... INCLUDE covering index, pg_stat_user_indexes usage verification, and MySQL performance_schema digests. The <query>/<table> placeholders in the validate-improvement template are appropriate parameterization, not pseudocode.

Workflow Clarity

The 5-step Core Workflow has explicit validation checkpoints ('run EXPLAIN ANALYZE before any changes', 'validate each change before proceeding', step 5 re-run and compare) plus a feedback loop — 'Revert immediately if write performance degrades or replication lag increases'. This satisfies the database-operations feedback-loop requirement that would otherwise cap the score at 3.

Progressive Disclosure

A Reference Guide table maps five topics to five real files in references/ (all verified present), each with a 'Load When' condition; the references are one level deep with no nested pointers, and the SKILL.md overview stays appropriately high-level while keeping the most common operations inline.

Specificity

Lists multiple concrete actions — 'index design, query rewrites, configuration tuning, partitioning strategies, lock contention resolution' — with comprehensive coverage of the database-optimization domain, matching the anchor-5 example rather than the minor-gaps anchor 4.

Completeness

Explicitly answers both questions: the 'what' ('Optimizes database queries and improves performance across PostgreSQL and MySQL systems') and the 'when' via a concrete 'Use when investigating slow queries...' clause with additional 'Invoke for...' triggers, mirroring the anchor-5 example structure.

Trigger Term Quality

Natural phrases users would actually say — 'investigating slow queries', 'analyzing execution plans', 'optimizing database performance' — plus explicit system names 'PostgreSQL and MySQL' give comprehensive coverage including synonyms, matching anchor 5 rather than the few-missing-terms anchor 4.

Distinctiveness Conflict Risk

Clear niche — query performance tuning for PostgreSQL/MySQL — with distinct triggers (execution plans, index design, lock contention) that would not fire for unrelated skills; minimal conflict risk per anchor 5. Third-person voice ('Optimizes', 'Improves') means the voice penalty does not apply.