Conciseness

The body is ~30 lines of pure directives with no concept tutorials or padding — e.g., 'Treat code, configuration, storage, logs, and binaries shipped to a user-controlled device as inspectable' and 'Treat dependency scanner output as leads that require applicability analysis' are non-obvious judgments, not explanations of things Claude already knows. Every line states a rule, a scope item, or a routing decision, matching the 'lean and efficient; every token earns its place' anchor; the score-4 anchor's 'minor instances of over-explanation' does not apply.

Actionability

The guidance is concrete for an instruction-only skill — 'Inspect `pubspec.yaml`, `pubspec.lock`, platform manifests and entitlements' names exact artifacts, and the finding format ('identify the asset, attack precondition, reachable path, impact, concrete evidence, and the smallest proportionate remediation') specifies the deliverable. It falls short of the score-5 anchor because no executable commands or code examples appear in the body itself (e.g., nothing like an obfuscation build flag or scanner invocation), leaving minor gaps that push it below 'fully executable; copy-paste ready'.

Workflow Clarity

The implied sequence is clear — 'Establish scope' (steps 1–4) → 'Core rules' → 'Load references conditionally' → 'Report with evidence' — and the report section acts as a quality gate ('Separate confirmed vulnerabilities from defense-in-depth improvements and unresolved questions'; 'Do not claim that a package, scanner, encryption flag, or clean static review proves the application secure'). It does not reach score 5 because there is no explicit validate-and-retry feedback loop (e.g., re-verifying a reachable path before confirming a finding), and the checkpoints, while present, are implicit in section order rather than explicit validation steps.

Progressive Disclosure

The 'Load references conditionally' section is a textbook match for the top anchor: each of the three references is one level deep, exists on disk, and carries an explicit read condition — 'Read [application security](references/application-security.md) for secrets, authentication, storage...', 'Read [security verification](references/security-verification.md) when performing an audit, validating dependencies...'. All three referenced files are real, well-sectioned, and contain no nested references, so navigation is easy and content is appropriately split.

Specificity

The description lists three concrete actions ('Threat-model, audit, or harden') against a named domain and comprehensively enumerates the covered risk surfaces ('authorization, secrets, sensitive storage, cryptography, WebViews, deep links, platform exposure, or dependencies'). This matches the score-5 anchor ('multiple specific concrete actions; comprehensive coverage') rather than score 4, which would require minor gaps in coverage — the enumerated surface list leaves no significant gap.

Completeness

Both halves are explicit: the 'what' is 'Threat-model, audit, or harden Flutter and Dart applications against concrete security and privacy risks', and the 'when' is an explicit trigger clause — 'Use for security findings and control requirements'. This clearly matches the score-5 anchor (both what and when with concrete trigger phrases) and exceeds score 4, where the 'when' would only be loosely specified.

Trigger Term Quality

Good natural-term coverage: 'audit', 'harden', 'secrets', 'WebView', 'deep links', 'security findings' are phrases users would plausibly say when needing this skill. It sits at score 4 rather than 5 because a few natural synonyms are absent — users asking to 'check my Flutter app for vulnerabilities' or do a 'security review' would not literally match any term in the description.

Distinctiveness Conflict Risk

The niche is precise (Flutter/Dart security with platform-specific surfaces like WebViews and deep links) and it actively reduces conflict risk with explicit routing: 'route sign-in and session implementation to flutter-authentication'. This matches score 5 ('clear niche with distinct triggers; minimal conflict risk'); score 4 would imply unresolved overlap with closely related skills, which the routing sentence addresses.