Conciseness

The body is dense and assumes Claude's competence, loading domain-specific facts (PMREM behavior, equirectangular wrapping, linear-space lighting) without padding basics; a few long sentences could be tightened, keeping it just below the fully lean anchor 5.

Actionability

As an instruction-only skill it gives concrete, specific guidance ("inward-facing dome with depth writes disabled and fog disabled", "Blend a pale warm horizon through a muted middle band into a cooler zenith") and names exact functions (makeSky, makeHills, makeStars); per the code-vs-instruction note the absence of code is not penalized, but a few details stop just short of fully copy-paste-ready specificity.

Workflow Clarity

Sections sequence the work (choose representation → build sky → map panorama → color/lighting → day/dusk/night → Verify) and the Verify section acts as a checklist checkpoint with feedback on what to look for, but the body is topical rather than a strict numbered step flow with explicit retry loops, so it sits at 4 rather than 5.

Progressive Disclosure

The ~45-line body is well organized into clear sections and ends with a clearly signaled one-level reference ("Read [REFERENCES.md](REFERENCES.md) for source inspection and official APIs"), but no bundle directories exist and REFERENCES.md is not present, so the referenced detail is not actually available — a minor organization gap that caps it at 4.

Specificity

The description enumerates several concrete capabilities ("procedural atmosphere or panorama, horizon haze, aligned sunlight, and coherent environment lighting"), but the active verbs are essentially limited to "Create", so it lists several specific actions with minor coverage gaps rather than the comprehensive multi-verb action set of a 5.

Completeness

It clearly states what the skill does ("Create a camera-correct sky background...") and explicitly answers when to use it with concrete trigger phrases via the "Use for..." clause, matching the anchor for a clear what-and-when pair.

Trigger Term Quality

"Use for architectural skies, outdoor 3D backgrounds, golden hour, and day-to-night sky transitions" supplies several natural phrases a user would say, but common synonyms a practitioner might also use (skybox, sky dome, HDRI, environment map) are absent.

Distinctiveness Conflict Risk

"3D sky background" is a clear niche with distinct triggers (architectural skies, golden hour, day-to-night transitions) and minimal overlap risk with unrelated skills; it uses third person with no first/second-person voice to penalize.