Conciseness

The body spends its tokens on version-gated engine facts Claude commonly misremembers (PG 11 default rewrite, MySQL 8.0.12 INSTANT, the 256-byte VARCHAR boundary, SHARE ROW EXCLUSIVE on ADD FOREIGN KEY) rather than explaining basics, but several verbatim documentation quotes run longer than the classification rule they justify and could be trimmed — the 4 anchor (efficient, minor over-explanation), not 5, and above 3 because nearly every paragraph carries a fact that changes a severity verdict.

Actionability

As an instruction-only skill the guidance is fully executable: an eight-category table with SQL examples and default severities, five engine checks each ending in an exact classification instruction ("Classify a plain CREATE INDEX on PostgreSQL as category 3: Warning with no size signal, Critical on a large table"), and a concrete output template with two worked rows and a count block — the instruction-skill equivalent of copy-paste-ready code covering the common cases.

Workflow Clarity

Steps 1-4 are clearly sequenced with explicit validation throughout: inputs recorded with "unknown" rather than guessed, unverified sizes reported as a band not a point value, every output row required to carry a basis, version-gated severities reported as ranges, and the "Unclassifiable statements" count plus the Anti-patterns section acting as a self-check and failure-mode checklist. The destructive/batch cap at 3 does not apply because the skill classifies only (its scope boundary excludes running migrations) and verification checkpoints are present at every step.

Progressive Disclosure

The single bundle file (references/engine-quick-reference.md, verified to exist) is clearly signaled and exactly one level deep: the body states what moved there (consolidated per-engine lock/rewrite tables, the three severity-flipping divergences, and the full worked example) while keeping the classification procedure inline — a clean match to the 5 anchor.

Specificity

The description lists multiple concrete operations ("rename or drop a column, add NOT NULL or a default, add an index or foreign key, change a type") and a concrete output ("Classifies each statement (additive, locking, breaking, data-loss) by lock and rewrite") in correct third-person voice — comprehensive coverage of the skill's scope, not just minor-gap coverage, so it fits the 5 anchor rather than 4.

Completeness

Both questions are answered explicitly: a trigger clause ("Use whenever someone asks if a database migration is safe to run in production: ...") and a clear what ("Classifies each statement ... by lock and rewrite") with concrete trigger phrases — a direct match to the 5 anchor.

Trigger Term Quality

Natural user phrases are well covered ("safe to run in production", "migration", "add an index or foreign key", "PostgreSQL or MySQL"), but common synonyms such as "schema change", "zero downtime", "lock", or "DDL" are absent — matching the 4 anchor (good coverage, a few natural terms missing) rather than 5, and clearly above 3 since keyword coverage spans both engines and all listed operations.

Distinctiveness Conflict Risk

It carves out a clear niche — production migration-safety classification for PostgreSQL and MySQL by lock and rewrite behavior — with triggers distinct from adjacent skills such as migration authoring or execution, so conflict risk is minimal.