Conciseness

Lean and dense with non-obvious knowledge: no concept explanations (nothing teaches what a CDN or VCL is), and sections are pure gotchas ("obj.ttl is only meaningful in vcl_hit", "beresp.* is only available in vcl_fetch", "req.request is deprecated — use req.method"), commands, or navigation. Every line carries information Claude would not reliably know from training.

Actionability

Mostly copy-paste ready: five complete executable VCL recipes, concrete pre-flight commands (curl with Host header, openssl s_client SAN check), and a precise common-mistakes list. Minor gap: the "VCL Table for Lookups" recipe presents an inline `table redirects { ... }` declaration as if it were uploadable VCL, but on a real service tables/edge dictionaries must be created via the API (as vcl-services.md's "Edge Dictionaries" endpoints document), and the recipe doesn't say so — matching the 4 anchor (concrete code with minor gaps) rather than 5.

Workflow Clarity

The Quick Start is a genuine pre-flight checklist with numbered validation steps and executable checks ("Verify the origin responds", "Check TLS certificate SANs"), an explicit error-recovery branch ("If HTTPS cert validation cannot be made correct but HTTP with the intended Host works, use an HTTP backend or fix the origin cert; never disable backend cert verification"), and a precise pointer to the full create-service workflow. This matches the 5 anchor: clear sequence, explicit validation, feedback loop.

Progressive Disclosure

Model structure: a 21-row Topics table where every row links a real (verified present) one-level-deep reference file with a per-topic "Use when..." routing column, an explicit boundary statement routing stats topics to the separate fastly-stats skill, and inline content limited to the highest-frequency gotchas. Navigation is easy and the split is appropriate, matching the 5 anchor.

Specificity

Uses concrete third-person verbs ("Configures, manages, and debugs") and enumerates specific capability areas: "service and backend setup, caching and VCL, security features like DDoS/WAF/NGWAF/rate limiting/bot management, TLS certificates and cache purging, the Compute platform, and the REST API". Coverage spans the platform surface comprehensively rather than with minor gaps, so it fits the 5 anchor rather than 4.

Completeness

Explicitly answers both questions: the "what" is the opening capability sentence, and the "when" is stated twice with concrete triggers ("Use when working with Fastly services or domains..." and "Also applies when troubleshooting 503 errors..."). Both are explicit and concrete, matching the 5 anchor exactly.

Trigger Term Quality

Natural user phrases are comprehensive: "working with Fastly services or domains", "setting up edge caching or origin shielding", "making Fastly API calls", "enabling products", plus concrete failure-mode triggers like "troubleshooting 503 errors or SSL/TLS certificate mismatches on Fastly" and "configuring logging endpoints, load balancing, ACLs, or edge dictionaries". Includes synonyms and error-level terms users would actually say, matching the 5 anchor.

Distinctiveness Conflict Risk

Clear niche anchored to a named platform throughout — "Fastly CDN platform", "NGWAF", "the Compute platform", "edge dictionaries" — with generic terms (rate limiting, TLS) always tied to Fastly context. Trigger phrases are vendor-specific enough that conflict with other CDN/security skills is minimal.