Conciseness

The body is ~43 lean lines with no padding: the Common Gotchas carry non-obvious, high-value facts (default port 7676 not 5000, the [local_server] requirement, dictionary vs ConfigStore config split) and the Quick Start is a minimal command block. The two-line intro establishes tool identity rather than explaining concepts Claude already knows, so it fits the 'every token earns its place' anchor.

Actionability

The Quick Start is copy-paste executable and covers the common path end-to-end ('cargo install --locked viceroy', 'fastly compute build', 'viceroy -C fastly.toml bin/main.wasm', 'fastly compute serve'), and the gotchas supply concrete values (exact TOML section names, the 127.0.0.1:7676 URL). This matches the 'fully executable, covers the common cases' anchor rather than the minor-gaps anchor at 4.

Workflow Clarity

The install -> build -> serve sequence is clear and correctly ordered, but there is no explicit verification checkpoint after starting the server (e.g., curling http://127.0.0.1:7676 to confirm it is up); the 'Access your app at http://127.0.0.1:7676' gotcha only implies validation. This is the 'clear sequence with minor validation gaps' anchor — not 5 because no explicit validate step exists, and not 3 because the sequence is complete and the destructive/batch validation cap does not apply to running a dev server.

Progressive Disclosure

The SKILL.md is a lean overview and all detail is pushed to four reference files presented in a table with a 'Use when...' navigation column; all four referenced files exist and contain no second-level references, so references are one level deep and clearly signaled. This matches the top anchor for well-signaled, one-level-deep navigation.

Specificity

The description lists multiple concrete actions — 'configuring fastly.toml for local backend overrides and store definitions', 'running Rust unit tests with cargo-nextest', 'adapting core WASM modules to the Component Model' — plus concrete failure symptoms '(connection refused, missing backends, store config)', giving comprehensive coverage of the skill's task surface. It exceeds the 4 anchor because there are no meaningful gaps in the action list.

Completeness

It explicitly answers what ('Runs Fastly Compute WASM applications locally with Viceroy, specifically for Rust and Component Model projects') and when via a fully enumerated 'Use when starting... configuring... running... debugging... adapting... or troubleshooting' clause. Both halves are explicit and concrete, matching the top anchor rather than the 'when could be more explicit' anchor at 4.

Trigger Term Quality

It covers natural user phrasing comprehensively: 'local Fastly Compute dev server', 'debugging Compute apps locally', 'troubleshooting local Compute testing issues', along with tool and file names users would quote verbatim (Viceroy, fastly.toml, cargo-nextest) and error symptoms like 'connection refused' and 'missing backends'. This matches the comprehensive-with-synonyms anchor rather than the 'a few natural terms missing' anchor.

Distinctiveness Conflict Risk

The niche is distinct (Fastly Compute local development with Viceroy, scoped to Rust and Component Model) and the description proactively resolves the closest overlap: 'For non-Rust Compute work or understanding the Compute API, prefer the fastlike skill instead'. This active disambiguation puts it at minimal conflict risk, above the minor-overlap anchor at 4.