Conciseness

Most content is genuinely non-obvious Three.js knowledge (ShaderMaterial vs RawShaderMaterial built-ins, onBeforeCompile injection points, GLSL1 vs GLSL3 texture functions), but the ~55-line "GLSL Built-in Functions" section (abs, sin, mix, dot, cross, normalize...) and basic gradient snippets (mix(colorA, colorB, vUv.y)) re-explain standard GLSL Claude already knows.

Actionability

The Quick Start and most pattern examples are complete, copy-pasteable ShaderMaterial configurations with matching uniform declarations, but several snippets are fragments: the noise "Usage" line (float n = noise(vUv * 10.0 + time);) has no JS context, the dissolve effect lacks its JavaScript wrapper and varying declarations, and the instanced example leaves "// Fill offsets..." with an undefined instanceCount.

Workflow Clarity

The content progresses coherently from Quick Start through material types, patterns, and debugging, and the Debugging section provides error-detection checkpoints (renderer.debug.checkShaderErrors, logging compiled shaders, visual debug outputs) — though it is a topical reference rather than an explicitly sequenced workflow, so minor sequence/checkpoint gaps remain.

Progressive Disclosure

The body has clear section headers and easy navigation, but no bundle files exist at all — the GLSL function reference, uniform type tables, and pattern library (~640 lines total) are all inlined in SKILL.md when much of this reference material clearly belongs in separate reference files.

Specificity

The trigger clause lists four concrete actions ("creating custom visual effects, modifying vertices, writing fragment shaders, or extending built-in materials") plus specific domain terms ("GLSL, ShaderMaterial, uniforms"), but the opening "what" is a topic list rather than verb-driven actions, leaving minor gaps versus a fully comprehensive action list.

Completeness

Both parts are explicit: the what ("Three.js shaders - GLSL, ShaderMaterial, uniforms, custom effects") and an explicit "Use when" clause with four concrete trigger phrases ("creating custom visual effects, modifying vertices, writing fragment shaders, or extending built-in materials"), matching the anchor-5 pattern of clear what plus explicit when with concrete triggers.

Trigger Term Quality

Good coverage of natural terms users would say — "Three.js shaders", "GLSL", "ShaderMaterial", "uniforms", "fragment shaders", "visual effects", "built-in materials" — but a few natural variations are missing, notably the literal phrase "vertex shaders" (only "modifying vertices" appears) and there are no synonyms like ".glsl".

Distinctiveness Conflict Risk

The Three.js/GLSL shader niche is clear with distinct technical triggers (ShaderMaterial, uniforms, GLSL), but "extending built-in materials" overlaps with the sibling threejs-materials skill referenced in the body, and full-screen effect work brushes against threejs-postprocessing — minor overlap risk with closely related skills.