The opening line "Image CDNs automatically optimize, resize, and convert images on-the-fly..." explains a concept Claude already knows, and format-conversion/optimization is repeated across the intro, Quick Reference, Fix, and Explain sections. It is not a 3 because of this redundancy and unnecessary explanation; it is not a 1 because the body is short and mostly tight, not padded with long background.

Names concrete providers ("Cloudinary, Imgix, or Cloudflare Images") and specific things to check, but "Configure an image CDN... for automatic optimization" is abstract with no sample URL, markup, or DevTools procedure. It is not a 3 because nothing is copy-paste ready; it is not a 1 because there is some concrete, specific guidance rather than pure abstraction.

Check → Fix → Code Review gives a light diagnostic sequence, and "describe how to confirm the fix in DevTools" nods at verification, but no explicit validation checkpoint is given. It is not a 3 because verification is only implicit, not an explicit step; it is not a 1 because the sections do sequence a review flow rather than leaving steps missing.

The body is a concise overview that signals a single one-level-deep reference — "see `references/rule.md`" — and that file exists, matching the well-signaled one-level-deep anchor. It is not a 2 because the reference is clearly labeled and the detail is appropriately split rather than inlined.

Names multiple concrete actions — "reviewing image assets, markup, and CDN or build transforms" and "Check encoded size, rendered size, loading strategy, and above-the-fold impact together" — with no vague filler. It is not a 2 because it lists several specific review actions rather than naming a domain plus one or two actions.

It answers both what (review/check the listed image attributes) and when via an explicit "Use when reviewing..." trigger clause. It is not a 2 because the trigger guidance is explicit, not merely implied, so the completeness cap of 2 for a missing trigger does not apply.

Covers natural frontend-performance terms a user would say — "image assets", "markup", "CDN", "loading strategy", "above-the-fold" — matching the good-coverage anchor. It is not a 2 because these are common variations rather than a single keyword; minor jargon like "build transforms" keeps it from being flawless but does not drop it a level.

Scoped to "Serve images from a CDN" with distinct checks (encoded/rendered size, loading strategy, above-the-fold) that form a clear niche unlikely to fire for non-image skills. It is not a 2 because the CDN-delivery framing is specific rather than a generic "works with image files" overlap.