Conciseness

The ~40-line body explains nothing Claude already knows (no Rust tutorials, no library comparisons) — every section is functional: a location note, a file index, a 12-row routing table, and six behavioral rules like "Load only the pages the task needs; guideline pages are the policy, workflow pages are the procedures." Matches the 5 anchor (lean, assumes competence, every token earns its place); there is no padded or over-explained passage that would justify 4.

Actionability

The routing table gives concrete, executable load instructions for 12 common cases ("Create a new Rust project → workflows/new-rust-project.md, guidelines.md"), which is actionable instruction-only guidance. However, Core Behavior bullets such as "Use the project's OO-leaning Rust default without forcing inheritance-shaped designs" and "Prefer strong, compiler-backed types over primitive-heavy APIs" are abstract directives not anchored to the page that elaborates them — minor gaps matching the 4 anchor rather than the fully-resolved 5 anchor.

Workflow Clarity

This is a single-purpose router skill under 50 lines, and its single action is unambiguous: consult the task→files table, load the listed pages, apply the rules, with an explicit fallback ("Ask one focused question only when required project context is missing"). The simple-skill exception applies and there are no destructive or batch operations requiring validation, so 5 is warranted rather than the 4 anchor's 'minor validation gaps'.

Progressive Disclosure

The body is a pure overview: a Supporting Files index of one-level-deep references (guidelines.md plus four workflow files), all clearly signaled with descriptions, and a routing table that names guideline page topics ("library/application errors, error propagation, public API evolution") for direct discovery. The nonstandard file location is explicitly documented ("supporting files live in .fabro/skills/rust-style-guide/ at the repository root... Read them with that prefix") and every link uses that prefix consistently. (Note: the referenced files are not present in this review bundle, but their documented repo-root location and consistent link prefix keep navigation unambiguous.) This matches the 5 anchor (clear overview, well-signaled one-level-deep references, easy navigation); the index→page hop lives inside guidelines.md and does not bury content in SKILL.md itself, so it does not fall to 4.

Specificity

Concrete actions are enumerated directly: "writing, reviewing, refactoring, or configuring Rust code", "setting up new Rust projects, investigating Rust performance, verifying library releases, or reviewing Rust code changes", plus a specific topic inventory ("Rust 2024/MSRV", "async/Tokio/concurrency", "testing with nextest", "rustfmt/Clippy", "unsafe/macro policy"). This matches the 5 anchor (multiple specific concrete actions, comprehensive coverage) rather than 4, which requires minor gaps in coverage — none are evident.

Completeness

Both questions are answered explicitly: what — "Apply this Rust style guide... Covers Rust 2024/MSRV, library vs application conventions, public API design..."; when — "Apply... when writing, reviewing, refactoring, or configuring Rust code" and "Also use when setting up new Rust projects, investigating Rust performance, verifying library releases, or reviewing Rust code changes." This mirrors the 5-anchor example structure (concrete what + explicit trigger phrases); 4 would require the 'when' to be less explicit, which it is not.

Trigger Term Quality

Natural user phrases are well covered: "reviewing", "refactoring", "new Rust projects", "Rust performance", "library releases". Matches the 4 anchor (good keyword coverage, a few natural terms missing): common variations like "Cargo", "crate", "workspace", "idiomatic Rust", or file extensions (".rs") are absent, keeping it below the 5 anchor; it is above 3 because coverage extends well beyond a couple of generic keywords.

Distinctiveness Conflict Risk

Every trigger is Rust-scoped ("Rust code", "Rust projects", "Rust performance", "reviewing Rust code changes"), establishing a clear niche with minimal risk of firing on non-Rust tasks. Matches the 5 anchor (clear niche, distinct triggers, minimal conflict risk); overlap with a generic code-review skill is prevented by the consistent Rust qualifier, so it does not fall to 4.