Conciseness

The per-line content is lean (dense code with terse comments, no padded prose), but the body encyclopedically restates standard three.js constructor signatures and API details (full listings of basic, advanced, and path-based geometries, BufferAttribute types) that Claude already knows. Anchor 3 ("mostly efficient but could be tightened") fits; not 4 because the trimming needed goes beyond minor instances, not 2 because there is no conceptual over-explanation.

Actionability

Fully executable, copy-paste-ready code throughout: complete custom BufferGeometry construction with attributes and indices, InstancedMesh setup with per-instance colors and runtime updates, morph targets, and geometry utilities. Specific examples cover the common cases for each topic. Undefined context variables (scene, material) are conventional for snippet-style examples and don't break executability in context.

Workflow Clarity

This is a reference document with no multi-step workflow; small ordered micro-patterns exist (setXYZ, needsUpdate = true, computeVertexNormals, computeBoundingBox in "Modifying BufferGeometry") but there are no explicit sequences or validation checkpoints for fragile operations like geometry mutation. Anchor 3 fits (some sequencing present, checkpoints implicit); not 2 because the structure is not rough or undefined, not 4 because checkpoint discipline is absent even where mutation requires ordered steps.

Progressive Disclosure

No bundle files exist, so ~550 lines of API reference are fully inlined in SKILL.md. The section structure is clear and navigable (better than anchor 2's minimal-structure example), but content that clearly belongs in separate files (the built-in/advanced/path-based geometry listings, interleaved buffers, morph targets) is inline with no offloading or reference pointers, matching anchor 3's "content that should be separate is inline".

Specificity

Lists several specific capability areas ("built-in shapes, BufferGeometry, custom geometry, instancing") though framed as domain nouns rather than the multiple concrete verbs of the top anchor; coverage has minor gaps (points/lines, geometry utilities). Clearly above anchor 3's 1-2 concrete actions, just short of anchor 5's fully comprehensive action list.

Completeness

Explicitly answers both "what" ("Three.js geometry creation - built-in shapes, BufferGeometry, custom geometry, instancing") and "when" ("Use when creating 3D shapes, working with vertices, building custom meshes, or optimizing with instanced rendering") with concrete trigger phrases, matching the anchor 5 example structure.

Trigger Term Quality

"creating 3D shapes, working with vertices, building custom meshes, optimizing with instanced rendering" are natural phrases users would say, giving good keyword coverage. Falls short of anchor 5 because common synonyms and variations (e.g., "3D geometry", "point cloud", "mesh optimization") are missing.

Distinctiveness Conflict Risk

The Three.js geometry niche is clear with mostly distinct triggers, but phrases like "building custom meshes" and "creating 3D shapes" carry minor overlap risk with closely related sibling skills (threejs-fundamentals, threejs-materials) referenced in See Also. Not anchor 5's minimal conflict risk, but well above anchor 3's broad overlap.