Conciseness

The body is dense commented code where comments carry non-obvious facts (e.g., "setIndex([...]) with a plain array picks Uint16 or Uint32 itself", "WebGPU backend draws Points at one pixel"), not filler. It falls short of score 5 because of minor trimmable over-explanation: the renderer/scene/camera boilerplate is fully duplicated between Quick Start and the WebGPU section, content Claude already knows from threejs-fundamentals. It is well above score 3 ('some unnecessary explanation') since nearly every token carries three.js-specific information.

Actionability

Nearly every section is complete, copy-paste-ready code with parameter-annotated constructors (e.g., "new THREE.CylinderGeometry(1, 1, 2, 32); // radiusTop, radiusBottom, height, radialSegments..." and the full InstancedMesh loop ending "instancedMesh.instanceMatrix.needsUpdate = true"). The one gap — the InstancedBufferGeometry WebGL shader path is deferred via a comment "declare `in vec3 offset;` ... (see threejs-shaders)" — is a minor gap that still leaves an actionable pointer, consistent with the score-5 anchor ('copy-paste ready code; specific examples cover the common cases').

Workflow Clarity

This is a reference/catalog skill, and where multi-step processes exist they are shown in order with explicit flags as checkpoints: "positions.needsUpdate = true; // upload the change", "Build the mesh after assigning morphAttributes so it picks up the targets", "mesh.instanceMatrix.needsUpdate = true; // flag after any batch of setMatrixAt calls". It is not score 5 because there are no explicit validate-and-recover loops, but nothing here is a destructive or batch data operation that would require one, and the rubric's cap for missing validation on destructive/batch workflows does not apply. It exceeds score 3 because sequencing that does exist is explicit and gotcha-flagged.

Progressive Disclosure

Headers are well-organized with easy navigation and a See Also section, but the entire ~495-line API catalog is inlined in SKILL.md with no bundle files at all (no references/, scripts/, or assets/ directories exist). The rubric's rationale ('SKILL.md should be an overview pointing to detailed materials') and its score-3 example ('200 lines of API reference that could be in a separate file') describe exactly this: the built-in constructor catalog and the WebGPU/TSL section are bulk reference content that could live one level deep in a references/ file. It is not score 2 because structure is strong, not 'minimal', and it is not score 4 because no content is offloaded — the score-4 anchor expects 'most content appropriately placed' across files. The simple-skill exception (score 5 for well-organized sections alone) applies only to skills under 50 lines.

Specificity

"Creating and shaping three.js geometry: built-in shapes, 3D text, vertex buffers and attributes, merging, instancing, batching, point clouds and lines, on WebGL or with WebGPU and TSL" lists multiple concrete capabilities with comprehensive coverage of the geometry domain, in third person. It exceeds the score-4 anchor ('several specific actions; minor gaps') because the enumerated capabilities span essentially the whole feature surface, including renderer backends.

Completeness

It explicitly answers both: the what ("Creating and shaping three.js geometry: built-in shapes, 3D text, vertex buffers and attributes, merging, instancing, batching, point clouds and lines") and the when ("Use when building 3D shapes or text, custom vertex data, custom meshes, instanced meshes, or point clouds") with concrete trigger phrases, exactly matching the score-5 anchor structure. The score-4 anchor ('when could be more explicit or specific') is surpassed since the when-clause enumerates five concrete triggers.

Trigger Term Quality

"building 3D shapes or text, custom vertex data, custom meshes, instanced meshes, or point clouds" uses phrases a three.js user would naturally say. It is not score 5 because some natural terms a user might say are absent from the trigger clause (e.g., "wireframe", "lines", "merging meshes", "BufferGeometry"), and it is clearly above score 3 ('some relevant keywords but missing common variations') because five distinct natural trigger phrases are present.

Distinctiveness Conflict Risk

The niche ("three.js geometry") is clear and triggers like "custom vertex data" and "instanced meshes" are geometry-specific. It sits at score 4 rather than 5 because the skill family referenced in See Also (threejs-materials, threejs-shaders, threejs-fundamentals) creates minor overlap risk for generic triggers like "custom meshes" or "3D shapes", which a user might say when they need materials or shaders instead.