Mostly executable and efficient, but the body repeats the same ShaderMaterial boilerplate (uniforms, vertex, fragment scaffolding) across many sections and includes a GLSL built-in function reference (abs, sin, mix, etc.) that Claude already knows, adding tokens that don't earn their place.

Provides fully executable, copy-paste-ready code for every concept - ShaderMaterial setup, uniform types, varyings, displacement, Fresnel, onBeforeCompile, instancing - with concrete, specific examples throughout.

Though largely a reference rather than a multi-step pipeline, the single actions are unambiguous and well-sequenced (Quick Start, then concepts, then extending materials, debugging, performance); per the simple-skill note, an unambiguous single-purpose reference qualifies for a 3.

Content is well-organized into clear sections but is a monolithic single-file reference (~640 lines) with no offloading of the deep API-style material (uniform type tables, GLSL function lists, injection-point catalogs) into separate reference files; the 'See Also' links point to sibling skills rather than bundle files.

Lists multiple concrete actions - 'GLSL, ShaderMaterial, uniforms, custom effects', 'modifying vertices, writing fragment shaders, or extending built-in materials' - naming a distinct technical domain and several specific operations.

Answers 'what' (GLSL, ShaderMaterial, uniforms, custom effects) and explicitly 'when' via the 'Use when creating custom visual effects, modifying vertices, writing fragment shaders, or extending built-in materials' trigger clause.

Captures natural terms users say - 'shaders', 'custom visual effects', 'uniforms', 'fragment shaders', 'modifying vertices' - with good coverage of phrasings a user would naturally use when requesting this skill.

The GLSL/ShaderMaterial/custom-effects niche is highly specific and unlikely to collide with general Three.js or materials skills, with distinct triggers tied to shader-specific tasks.