Conciseness

The body is dense and directive with essentially no padding and no explanations of concepts Claude already knows — every bullet issues guidance like "第一句落在核心判断或读者真正关心的疑惑上" and "推导只展开承重步骤". It sits at 'efficient; minor instances of over-explanation that could be trimmed': the condition-change idea recurs across 理解标准 #4 ("在原情境里改变一个关键条件"), 公式与原理 ("同一情境改变一个变量"), and Gotchas, and a few clauses in 中文表达 elaborate past the point a competent model needs, so it is not the fully lean 5.

Actionability

For an instruction-only skill, the guidance is concrete and executable: it specifies deliverable format ("自测题与参考答案分开放，答案放在末尾"), concrete techniques ("用简单数值跑通一次", "先把意思落到具体情境，再给名称"), a pre-delivery check ("按「会这样跟一个聪明朋友说话吗」检验口语"), and three worked example briefs in Examples. It falls short of 'fully executable / copy-paste ready' only because there is no sample of the actual output shape (e.g., a short model explanation or self-test question with its answer), leaving minor gaps; it is well above the pseudocode-level 3.

Workflow Clarity

The skill defines explicit completion criteria (理解标准 1-5: 知道为什么需要它 / 能辨认 / 能解释结果 / 能随条件改判断 / 能迁移) plus pre-delivery checkpoints ("交付前按「会这样跟一个聪明朋友说话吗」检验口语" and "必要时用可用计算工具复算，检查单位、比例、正负号和舍入"). No destructive or batch operations exist, so no validation cap applies. It matches 'clear sequence with most checkpoints present; minor validation gaps' — the step order (assess reader → explain → self-test → deliver) is implicit in the topic sections rather than laid out as a numbered pipeline, which the skill justifies ("组织方式由内容决定") but still leaves the sequence slightly less explicit than the 5.

Progressive Disclosure

The skill is a self-contained, well-organized single file with seven clear section headers (读者与交付, 理解标准, 公式与原理, 中文表达, 证据与版式, Gotchas, Examples), no bundle files, and no content that warrants external references — the ~62-line body is entirely overview-level guidance. Per the simple-skill guidance, well-organized sections with no need for external references score at the top; navigation is trivial and nothing is buried or inlined that belongs elsewhere.

Specificity

The description lists several concrete capabilities — "讲到能辨认、能推导、能迁移" and "接通具体情境、判别依据、运作过程和成立条件" — over the named domain of "概念、公式、机制与原理". This matches the 'lists several specific actions; minor gaps in coverage' anchor; it is not a 5 because the actions are capability outcomes (recognize, derive, transfer) rather than a fully comprehensive list of concrete operations, and it is clearly above the 1-2-action level of a 3.

Completeness

It explicitly answers both what ("把概念、公式、机制与原理讲到能辨认、能推导、能迁移：用通俗中文接通具体情境、判别依据、运作过程和成立条件") and when (a literal "USE WHEN" clause with concrete trigger phrases, further sharpened by a "NOT FOR" exclusion list). This directly matches the top anchor: clear what AND when with concrete trigger phrases, in descriptive voice with no first/second person.

Trigger Term Quality

Natural user phrasings are well covered: 「通俗易懂地讲解」「讲透这个概念或公式」「费曼讲解」「ELI5」, plus the explicit skill-name invocation (用户调用 ljg-explain) and "希望从零理解一个知识点并能用于新情境". It fits 'good keyword coverage; a few natural terms missing' — common variations like 「解释一下 X」「大白话讲讲」「这是什么意思」 are absent, so it falls just short of the comprehensive-synonym anchor at 5.

Distinctiveness Conflict Risk

The niche is fairly clear — plain-language conceptual explanation in Chinese, with quoted trigger phrases — and the "NOT FOR 单纯润色或翻译、整篇伴读、整本书或论文解读、只要求形式证明或操作步骤" clause actively fences off adjacent skills. It matches 'mostly distinct; minor overlap risk with closely related skills' because general explanation/Q&A skills could still overlap on ordinary 「解释一下」 requests that aren't among the listed triggers; the explicit skill-name trigger keeps conflict low but not minimal.