Conciseness

The body is dense — tables of defaults, anti-patterns, and EXPLAIN signals plus short code blocks, with almost no conceptual padding. It loses a point for a handful of statements Claude already knows ("Read replicas can lag", "Each index increases write cost…", "Do not use deep OFFSET pagination… it makes the server scan and discard rows") and for repeating the SKIP LOCKED caveat in both the Version Check and Transactions sections. Not 5, but far from the verbosity of anchor 3.

Actionability

Nearly every section delivers copy-paste-ready material: complete CREATE TABLE/INDEX statements, the upsert in both engine-compatible forms, a keyset-pagination query with its backing index, SQLAlchemy and mysql2 pool configs, a ready ini configuration block, and diagnostic SQL. This matches anchor 5 — fully executable guidance covering the common cases — and exceeds anchor 4, where only minor gaps would be tolerated.

Workflow Clarity

A coherent flow exists — 'Start by identifying the engine and version' leads in, and the Output Expectations section requires a validation plan (EXPLAIN, migration dry run, lock/deadlock check, rollback criteria) with per-issue guidance like 'Use EXPLAIN before adding or changing an index' and a bounded deadlock retry loop. It falls short of anchor 5 because validation checkpoints are distributed across sections rather than forming one explicit validate-then-fix-then-retry sequence for the risky migration path. Since database operations demand feedback loops, this is not capped at 3 — the loops are present, just not consolidated.

Progressive Disclosure

There are no bundle files at all (no references/, scripts/, or assets/), so ~413 lines of reference material — schema defaults, full-text search, security, connection pools, and a full server configuration block — are all inlined in SKILL.md. Sections are well-headed and navigable, but content that clearly belongs in separate reference files is inline, which is exactly anchor 3; anchor 4 would require most content to be appropriately placed in separate files with clear references.

Specificity

The description enumerates six concrete areas — "schema, query, indexing, transaction, replication, and connection-pool patterns" — but presents them as topic nouns rather than the action verbs of the top anchor ("Extract… fill… merge"), leaving minor gaps in coverage. It is clearly above anchor 3 because multiple specific capabilities are listed, not just 1-2.

Completeness

Both halves are explicit: the what is the six named pattern areas "for production backends" and the when is a concrete "Use when designing MySQL or MariaDB schemas and indexes, or when a query, transaction, or replica lags" clause. This matches the anchor-5 example's structure of explicit what plus concrete trigger phrases, so it cannot be capped at 4.

Trigger Term Quality

Natural phrases users would say are present — "designing MySQL or MariaDB schemas and indexes", "when a query, transaction, or replica lags" — but common variations like "database", "slow query", "deadlock", and "migrations" are missing. Good coverage rather than comprehensive synonym coverage, so it sits between the 3 and 5 anchors, noticeably above the midpoint.

Distinctiveness Conflict Risk

MySQL and MariaDB are named explicitly with engine-specific triggers (replica lag, MariaDB syntax divergence implied), carving a clear niche separate from adjacent skills like a generic postgres-patterns or backend-patterns skill. Overlap risk is minimal, matching the anchor-5 'clear niche with distinct triggers'.