Conciseness

The ~24-line body is pure directive prose — "Reproduce first.", "When stuck, instrument. Read the actual error and the actual state. Do not guess." — with zero explanation of concepts Claude already knows and every token earning its place, matching the level-5 anchor exactly. It does not fall to level 4 because no over-explanation instances exist to trim.

Actionability

Though code-free, the guidance is highly concrete per the instruction-skill scoring note: it names specific artifacts ("config files, caches, lock files, serialized state"), specific bug-hiding anti-patterns ("Guards, retries, swallowed errors, clamped values, and discarded state"), and a precise stopping criterion ("until the answer is a wrong decision in the code"), covering the common cases like the level-5 anchor.

Workflow Clarity

This is a simple single-purpose skill under 50 lines, so the simple-skill exception applies: the Pattern list is an unambiguous ordered procedure ("Reproduce first" → why-chain with an explicit termination condition → "When stuck, instrument" as error recovery), and it involves no destructive or batch operations that would impose a validation cap.

Progressive Disclosure

The skill is under 50 lines with no need for external references (no references/, scripts/, or assets/ bundle exists), and the body is cleanly organized into an intro definition, a **Why** section, and a **Pattern** checklist — exactly the well-organized-sections case the rubric scores at level 5.

Specificity

The description names several concrete actions — "Trace each symptom back to the first place the system went wrong and fix it there" plus the specific guard rule "A guard is a fix only when the state it handles is legitimate" — which goes beyond the 1-2 actions of the level-3 anchor, though it stops short of the broad multi-action coverage of level 5.

Completeness

Both questions are explicitly answered: "Apply when debugging" gives a concrete when-trigger, and "Trace each symptom back to the first place the system went wrong and fix it there" states exactly what the skill does, matching the level-5 anchor's clear-and-explicit both-what-and-when pattern. It is not level 4 because the when clause is already concrete rather than needing more specificity.

Trigger Term Quality

"Apply when debugging" supplies the single most natural trigger term, reinforced by "symptom", "trace", and "fix" — comparable keyword density to the level-4 anchor — but common variations like "bug", "error", or "root cause" are absent, keeping it below level 5.

Distinctiveness Conflict Risk

The symptom-vs-root-cause framing carves a clear niche that most skills would not match, but the broad "debugging" trigger could overlap with closely related debugging-methodology or tooling skills, fitting the level-4 anchor (mostly distinct, minor overlap risk) rather than level 5.