Conciseness

The body is dense and prescriptive — specific values like "bcrypt (≥12 rounds)", "about 10 attempts per 15 minutes", "`169.254.169.254`", and non-obvious caveats like the DNS-rebinding TOCTOU gap and "in-memory counters silently become `max × instances`" earn their tokens. It sits at anchor 4 rather than 5 because some material assumes less competence than needed: the STRIDE table, the "Common Rationalizations" table (10 rows of rebuttals), and repeated trust-boundary explanations in two sections could be trimmed without losing guidance.

Actionability

Guidance is largely concrete and directive — named algorithms and parameters ("`sameSite: 'lax'` or `'strict'`", "`default-src 'self'`"), exact commands ("`npm audit signatures`"), and precise conditions ("resolve **all** DNS records and reject any private or reserved address"). Per the scoring note, absent code is not penalized in an instruction-only skill, but some directives remain policy-level without executable detail ("a documented fail-closed policy", "pin the resolved IP", "inspect the pending script source"), matching anchor 4's "concrete code or commands with minor gaps" rather than anchor 5's fully copy-paste-ready coverage.

Workflow Clarity

Multi-step processes are clearly sequenced with checkpoints: the four-step threat-model process with a stop condition ("If you can't name the trust boundaries... you're not ready"), the four-step dependency workflow with validation ("stop on disagreement", "verify with a clean frozen/immutable install"), the three-condition pre-check for destructive operations, and a full Verification checklist. It falls short of anchor 5 because error-recovery feedback loops are thin in the body — most stop-conditions ("log the rejected target and stop") halt rather than loop back, and full recovery guidance is deferred to references.

Progressive Disclosure

Structure is genuinely good: the body is an overview of rules, each control section links one level deep to real, verified anchors in references/hardening-patterns.md, and navigation is explicitly paced ("Open the section you need when you reach that code, not before"). It misses anchor 5 because the body references `../../references/security-checklist.md` three times — including as the centerpiece of the Review Checklist section — and that path escapes the bundle and does not resolve, leaving a dangling, unverifiable reference within otherwise clean navigation.

Specificity

The description names concrete activities — "auditing an input handler for vulnerabilities", "checking a login flow is safe against the OWASP Top Ten", "triaging package-manager audit findings", "assessing supply-chain risk in a new package" — which is several specific actions with only minor gaps. It does not reach anchor 5 because the core 'what' ("Hardens code against vulnerabilities") is broad, and a few concrete sub-capabilities (headers/CORS, rate limiting, uploads) are only implied rather than named; it is clearly above anchor 3, which expects only 1-2 concrete actions.

Completeness

It explicitly answers 'what' ("Hardens code against vulnerabilities") and 'when' with four separate concrete "Use when..." clauses covering auditing, feature building, dependency/supply-chain work, and privacy compliance. This squarely matches anchor 5 (both what and when with concrete trigger phrases); anchor 4 would require the 'when' to be less explicit, which is not the case here.

Trigger Term Quality

It comprehensively covers natural phrases a user would actually say: "vulnerabilities", "user input", "authentication", "login flow", "OWASP Top Ten", "untrusted data", "user sessions", "third-party services", "supply-chain risk", "personal data", "GDPR", "CCPA", plus tool-adjacent terms like "audit findings". This matches anchor 5's standard of comprehensive natural-term coverage including synonyms; anchor 4 would require noticeable missing variations, and none are evident.

Distinctiveness Conflict Risk

The security-hardening niche is clearly staked out with distinctive triggers (OWASP Top Ten, supply-chain risk, GDPR/CCPA, audit findings) unlikely to fire for unrelated skills. It fits anchor 5's "clear niche with distinct triggers; minimal conflict risk"; there is only faint overlap risk with a generic code-review skill, which anchor 4 would describe as more than minor.