The body is lean and assumes Claude's competence — it never explains what functions, exceptions, or layers are, and every section (principle, methodology, five checks, Quantify, red flags, exemptions, output contract) earns its place. The recurring 'severity grading belongs downstream' framing is repeated across three sections, but it is purposeful emphasis on a core design decision rather than concept padding, so it stays at score 3.

It gives concrete, executable guidance: fixed classification tags (core/down/up/cross-cutting), a named decision rule-of-thumb, five review checks each specifying exactly what to record (hit yes/no + file:line + raw count), and a numbered output contract. This is an instruction-only review skill, and the guidance is specific and copy-ready rather than abstract, matching the score-3 anchor.

The methodology is a clearly sequenced 1–6 process with an explicit validation feedback loop ('Re-read for level… If not, repeat from step 1') and a 'Keep the change minimal' guardrail, and the review method lists five ordered checks with a defined recording format. It is not score 2 because the checkpoint and error-recovery loop are explicit, not merely implicit.

The skill is a single self-contained SKILL.md with no bundle files and no nested references, organized into well-signaled sections (Scope, When to use, The principle, Methodology, Review method, Quantify, Red flags, Exemption checklist, Output contract). Per the simple-skill scoring note, well-organized content with no need for external references scores 3.

The description names multiple concrete actions — 'review code through the single level of abstraction / layered error handling lens', 'reports detections, raw-count measurements, and move directions' — matching the score-3 anchor for listing several specific actions. It is not score 2 because it goes beyond naming a domain plus a few actions to enumerate distinct sensor outputs.

It explicitly answers both what ('reports detections, raw-count measurements, and move directions') and when ('Invoke only when the user explicitly asks', 'Apply only when the user explicitly requests this lens'). It is not score 2 because the when-clause is explicit, not merely implied.

It surfaces the lens by its technical name ('single level of abstraction / layered error handling'), which a knowledgeable user would say, but the description itself lacks the common layperson variations (e.g. 'function does too much', 'errors handled above/below') that the body later lists. It is not score 3 because the trigger keywords are jargon-heavy rather than a broad spread of natural terms.

The niche is sharply defined ('single level of abstraction / layered error handling' lens) and double-gated to fire only on explicit request, with general reviews deferred to other lenses, making false triggers unlikely. It is not score 2 because the gating removes meaningful overlap with sibling review skills.