Conciseness

Mostly efficient, judgment-dense prose (bad-vs-good mitigation table, 'if you can't write the test, you don't have the mitigation, you have an intention', the trust-boundary test for when to skip), but the STRIDE category table and the DFD-notation list ('External entities (rectangles)... Processes (circles)...') re-explain standard security concepts Claude already knows. Not 4 because two full sections are padding Claude doesn't need; not 2 because the majority of the body adds non-obvious judgment and templates.

Actionability

Fully actionable instruction-only guidance: an executable Mermaid DFD example, a worked STRIDE-per-element table template, the abuse-case sentence format with three worked examples, a bad-vs-good mitigation comparison with concrete specifics (5 req/min per user IP with Redis-backed counter; KMS envelope encryption with 90-day rotation), and a copy-paste output document template. These cover the common cases end-to-end.

Workflow Clarity

The body is organized as Shostack's four questions with Steps 1-4 in strict sequence, and Step 4 is itself a validation checkpoint: coverage check ('every element... every threat... every mitigation has an owner and a deadline'), adversarial second pass to break blind spots, and trace-to-tests. Explicit validation steps and error-recovery guidance ('if you can't write the test...') match the top anchor.

Progressive Disclosure

No bundle files exist (references/, scripts/, assets/ are absent), and the single 210-line body is well-sectioned with clear headers, no buried or nested references, and an external-reading list cleanly isolated at the end. Good structure and appropriately self-contained; not 5 because the length exceeds what the simple-skill exception rewards and a couple of sections (STRIDE reference table, external references) are natural candidates for split-out files if the bundle grows.

Specificity

"Run a structured threat-modeling session for a new feature, system, or architecture — STRIDE, attack trees, data flow diagrams, abuse cases" names the domain and several concrete artifacts (STRIDE analysis, attack trees, DFDs, abuse cases), with only minor gaps in coverage (e.g., risk-mitigation output format is implied rather than named). Not 5 because the actions are framework names rather than a fully enumerated list of what the skill produces; not 3 because coverage clearly exceeds 1-2 actions.

Completeness

It explicitly answers both questions: the what ("Run a structured threat-modeling session... STRIDE, attack trees, data flow diagrams, abuse cases") and the when ("Use when the user mentions 'threat model,'... or needs strategic security thinking before code is written") with concrete trigger phrases, matching the anchor-5 example structure.

Trigger Term Quality

The trigger list is comprehensive and natural: 'threat model,' 'threat modeling,' 'STRIDE,' 'attack tree,' 'abuse case,' 'data flow diagram,' 'DFD,' 'security architecture review,' 'security review,' 'design review,' 'pre-implementation security,' 'shift left,' 'what could go wrong' — covering synonyms, an acronym, and a colloquial phrasing a user would actually say.

Distinctiveness Conflict Risk

The design-time framing ('before code is written,' 'pre-implementation security') carves a clear niche distinct from code-audit skills, but generic triggers like 'security review' and 'design review' carry minor overlap risk with audit/review skills. Not 5 because those broad phrases could plausibly fire for a different security skill; not 3 because the specialized trigger terms dominate.