Conciseness

The body is lean, imperative, and assumes Claude's competence throughout — e.g. '`Ast<Node>` for syntax-local checks', 'Set `FixKind::Safe` only when no reachable input changes behavior', 'Prefer ranges, syntax nodes, tokens, and compact enums in `State`'. Every line is Biome-specific policy or command; nothing explains concepts Claude already knows, matching anchor 5 ('every token earns its place').

Actionability

Fully executable guidance: copy-paste scaffolding and test commands ('just new-js-lintrule useMyRule', 'just test-lintrule useMyRule', 'just gen-rules', 'just gen-configuration', 'just f'/'just l') plus concrete APIs and artifacts ('declare_lint_rule!', 'type Options', 'options.json', 'visited_kinds', 'FixKind::Safe'). This matches anchor 5 ('copy-paste ready commands; specific examples cover the common cases').

Workflow Clarity

A clear 6-step numbered sequence with explicit validation checkpoints ('then inspect snapshots', 'Run required analyzer codegen and the narrowest tests', 'Run `just f` and `just l` as required by `AGENTS.md`') and a final Review Checklist. It falls short of anchor 5 only because there is no explicit error-recovery feedback loop (e.g. what to do when a snapshot or test disagrees), which is instead delegated to 'testing-codegen'; anchor 4's 'clear sequence with most checkpoints present; minor validation gaps' is the closest fit.

Progressive Disclosure

No bundle files exist; the body stays a lean overview and defers detail through clearly signaled, one-level-deep references: 'Load `diagnostics-development` for message structure...', 'Follow the analyzer guide sections **Rule Options**, **Merge**, and **Documenting Options**', and the terminal References section listing repo paths. Nothing that belongs elsewhere is inlined, matching anchor 5 ('clear overview with well-signaled one-level-deep references').

Specificity

The description enumerates comprehensive concrete capabilities: 'creating or modifying Biome lint rules or assists, including analyzer queries, semantic bindings, rule state, code actions, fix safety, options, registration, and end-user rule rustdoc'. This spans the full rule-development lifecycle, matching the anchor-5 pattern of multiple specific concrete actions with comprehensive coverage rather than anchor 4's 'several specific actions; minor gaps'.

Completeness

Both questions are answered explicitly: 'what' via the enumerated capability areas and 'when' via the concrete trigger 'Use this skill when creating or modifying Biome lint rules or assists', plus escalation triggers ('Also load diagnostics-development for substantial message/advice design'). It clearly matches anchor 5; it is not anchor 4 because the 'when' is explicit and specific rather than generic.

Trigger Term Quality

Natural domain keywords are well covered — 'lint rules', 'assists', 'code actions', 'fix safety', 'rustdoc', 'fixture or snapshot mechanics' — but a few terms a user would plausibly say are missing (e.g. 'suppression', 'autofix'/'safe fix', 'nursery'/'changeset'). This matches anchor 4 ('good keyword coverage; a few natural terms missing') and not anchor 5, which requires synonyms and variations.

Distinctiveness Conflict Risk

The description is tightly anchored to a niche ('Biome lint rules or assists') with distinct triggers, and it explicitly partitions concerns with sibling skills (diagnostics-development for message/advice design, testing-codegen for fixtures/snapshots). This is a clear niche with minimal conflict risk, matching anchor 5.