The body is short and lightly padded rather than verbose, but several lines are restatements Claude already knows (e.g. 'A single main landmark allows keyboard and screen reader users to jump directly to the primary content') and the 'Code Review' section largely re-describes the skill rather than adding load-bearing detail, so it is mostly efficient but could be tightened.

The 'Check' step gives a concrete counting heuristic ('Count the number of <main> elements or elements with role=main') and 'Fix' gives a remediation, but there is no executable command, selector, or code snippet in the body itself — the only runnable examples live in references/rule.md — so guidance is concrete but incomplete in SKILL.md.

The Check / Fix / Explain / Code Review sections provide a recognizable sequence, but there is no validation checkpoint confirming the fix actually yields exactly one <main> (a verification step exists only in the reference file), so checkpoints are implicit rather than explicit.

The body is a concise overview with a single clearly signaled one-level-deep reference ('see references/rule.md'), the referenced file exists, and content is appropriately split between the overview and the detail file rather than nested multiple levels, matching the well-organized reference anchor.

Quotes a concrete domain ('rendered HTML, interactive components, or design-system patterns') and lists several specific checks ('keyboard behavior, focus flow, accessible names, and screen-reader output'), but these are generic review activities rather than concrete actions tied to the single main-landmark rule, and the repeated phrase 'related to Use exactly one main landmark' reads as a label rather than a listed action.

It explicitly answers 'when' via the 'Use when reviewing...' clause and 'what' via the enumerated inspection steps, satisfying both halves with an explicit trigger; not score 2 because the trigger clause is present rather than merely implied.

It opens with 'Use when reviewing rendered HTML, interactive components, or design-system patterns' which are reasonable natural phrases, but it omits the common variations a user would actually say ('main landmark', 'one main', 'screen reader jump to main', 'skip to content') and leans on the title-phrase rather than user vocabulary.

The description is scoped to a specific accessibility rule, but the phrase 'reviewing rendered HTML, interactive components, or design-system patterns' is broad and would overlap with many other accessibility/design-system skills, so conflict risk remains moderate.