Extending Claude Code: Hooks (Deterministic) vs. CLAUDE.md (Advisory), Skills, Subagents, Plugins, Wiring Up an MCP Server, CLI Tools First

Interview questions

• Why are hooks more reliable than rules in CLAUDE.md? What belongs in each? Give one rule you would move from CLAUDE.md to a hook.为什么 hooks 比 CLAUDE.md 里的规则更可靠？各适合放什么？举一个你会从 CLAUDE.md 挪到 hook 的例子。

  Common in ChinaCommon overseasBasic#hooks#claude-md

  How to reason about it · think before answering

  1. This tests the systemic position of advisory versus deterministic, not feature recall. 'Hooks are scripts that run automatically' is a description; explain why model adherence is not program execution.
  2. Breakdown: CLAUDE.md enters the model's context as text and the model decides after reading — adherence is high but not total, drops as the file grows, and can be lost after compaction. A hook is a script Claude Code itself runs unconditionally at fixed lifecycle points (PreToolUse, PostToolUse, Stop), with the exit code deciding whether to block, independent of the model's judgment.
  3. One-line rule: actions that allow zero exceptions become hooks; preferences that usually apply stay in CLAUDE.md. The inverse also holds — delete rules the model follows by default, convert must-always rules into hooks, and the file shrinks.
  4. Make the example concrete: 'run lint and tests before committing' is occasionally skipped as text; as a Stop hook, failing tests exit 2 and the model receives the summary and keeps fixing. 'Never edit migrations/' becomes a PreToolUse hook matching Edit|Write that exits 2 on a path hit.
  5. Follow-ups: risks? Hooks are code running on your machine — a cloned repo's hooks execute, and headless mode shows no trust dialog; a Stop hook is overridden after 8 consecutive blocks to prevent loops.

  分析过程 · 先想清楚再作答

  1. 这题考的是「建议 vs 确定性」的系统位置，不是背功能名。答「hooks 是自动执行的脚本」只是描述，要说清为什么模型的遵守率不等于程序的执行率。
  2. 拆法：CLAUDE.md 的内容作为文字进入模型上下文，由模型读后决定怎么做——遵守率高但不是百分之百，文件越长越低，压缩后还可能丢失。hook 是 Claude Code 程序在固定生命周期点（PreToolUse / PostToolUse / Stop 等）无条件运行的脚本，由退出码决定拦不拦，与模型的判断无关。
  3. 判据一句话：一次例外都不能有的动作做成 hook；通常应该这样的偏好写进 CLAUDE.md。反向操作也成立：CLAUDE.md 里模型已经默认遵守的删掉，必须百分之百的换成 hook，文件就短了。
  4. 例子要具体：「提交前跑 lint 与测试」——作为文字它偶尔会被跳过；做成 Stop hook，测试不过 exit 2，模型收到失败摘要继续修，直到通过；「不许改 migrations/」做成 PreToolUse hook 匹配 Edit|Write，路径命中就 exit 2。
  5. 可预期的追问：hook 有没有风险？有——它是代码，跑在你机器上，clone 陌生仓库时别人的 hook 会执行，无头模式没有信任对话框；Stop hook 连续 8 次阻止后会被放行防死循环。

  Key points

  • CLAUDE.md is text the model reads and then decides on — high but not total adherence
  • A hook is a script the program runs unconditionally at lifecycle points; the exit code decides, not the model
  • Zero-exception actions become hooks; usual preferences stay in CLAUDE.md
  • Examples: pre-commit tests as a Stop hook; a migrations deny as a PreToolUse hook

  答题要点

  • CLAUDE.md 是送进上下文的文字，由模型读后决定，遵守率高但不是百分之百
  • hook 是程序在固定生命周期点无条件跑的脚本，退出码决定拦不拦，与模型判断无关
  • 一次例外都不能有的做 hook；通常应该这样的写 CLAUDE.md
  • 例：提交前测试改成 Stop hook；禁改 migrations 改成 PreToolUse hook
• What is progressive loading for skills, why does it save context, and how should the description be written?skill 的渐进式加载是怎么回事？为什么能省上下文？description 应该怎么写？

  Common in ChinaCommon overseasIntermediate#skills#context

  How to reason about it · think before answering

  1. This tests the on-demand loading idea and whether you have actually written a skill. The third part separates candidates: a poorly written description makes the skill dead weight.
  2. Mechanism: at session start only each skill's one-line description from the frontmatter is resident; the body loads when the model judges the task relevant or the user types /name. Body length therefore barely affects daily cost, so it can hold long procedures, examples, and caveats.
  3. Contrast with CLAUDE.md: loaded in full every session, a fixed cost; a procedure used twice a week wastes the window the rest of the time. Moving such content into skills is how CLAUDE.md keeps shrinking after pruning.
  4. Writing the description: state what it does plus the phrases a user would say, about a hundred words; too broad triggers on unrelated tasks, too narrow never triggers. Add disable-model-invocation: true for side-effecting workflows so only /name invokes them; $ARGUMENTS takes parameters; allowed-tools pre-approves commands.
  5. Follow-ups: how do you test triggering? Try several natural phrasings and check whether the body loaded. Skill versus subagent: a skill loads a manual into the current context; a subagent opens a separate context to do work; they compose.

  分析过程 · 先想清楚再作答

  1. 这题考的是「按需加载」这个设计思想，以及你有没有真写过 skill。第三问是区分度：description 写不好，skill 就形同虚设。
  2. 机制：会话开始时只有每个 skill 的 frontmatter 里那一行 description 常驻上下文；当模型判断当前任务相关、或用户输入 /name 时，正文才被读进来。所以正文长短几乎不影响日常成本，可以放几十步的流程、示例、注意事项。
  3. 对比 CLAUDE.md：它整份每次加载，是固定成本；一周只用两次的流程放进去等于其余时间白占窗口。把这类内容挪到 skill，是「删到不能再删」之后 CLAUDE.md 还能继续变短的主要手段。
  4. description 的写法：说清做什么 + 用户会怎么说（触发词），一百来字；太泛会被无关任务误触发，太窄永远触发不到。有副作用的流程（部署、发消息）加 disable-model-invocation: true 只允许手动 /name 触发。$ARGUMENTS 接参数，allowed-tools 预授权命令。
  5. 可预期的追问：怎么测 skill 有没有被触发？用几个自然语言说法试，看模型是否读了正文；再追问「skill 与 subagent 的区别」——skill 是在当前上下文里加载一份说明书，subagent 是另起一个上下文去做事，两者可以组合。

  Key points

  • Only the description is resident; the body loads on invocation, so body length barely costs
  • CLAUDE.md loads in full each time; moving occasional procedures to skills keeps it short
  • Write the description as what it does plus how users phrase it, about a hundred words
  • Side-effecting workflows get disable-model-invocation; $ARGUMENTS carries parameters

  答题要点

  • 只有 description 常驻，正文在被触发时才加载；正文长短几乎不影响日常成本
  • CLAUDE.md 整份每次加载；偶尔用的流程挪进 skill 是让它继续变短的手段
  • description 写「做什么 + 用户会怎么说」，一百来字，不泛不窄
  • 副作用流程加 disable-model-invocation；$ARGUMENTS 接参数
• What problem do subagents solve? Do they see the main conversation's history? When should you not use one?subagent 解决了什么问题？它看得到主会话的历史吗？什么时候不该用？

  Common in ChinaCommon overseasIntermediate#subagents#context

  How to reason about it · think before answering

  1. The key is the problem solved: protecting the main conversation's context window, not the side benefits of parallelism or specialization. The second part is a common misconception; the third tests judgment.
  2. Chain: research and review tasks read a lot and keep little — thirty files for one conclusion. Done in the main session, all thirty land in the window and crowd out the actual implementation. A subagent has its own context window, reads everything, and returns only a summary; the main session pays only for the summary.
  3. Second part: no. A subagent starts with the system prompt, the task you delegated, CLAUDE.md, and a git status snapshot — not the main history, your earlier file reads, or previously loaded skills. That is both a limit and a strength: a reviewer without the memory of having just written the code finds more faults, which is what adversarial review in D5 relies on.
  4. Configuration: .claude/agents/<name>.md with tools restricting what it may use (no Edit for a reviewer) and model to pick a cheaper or stronger model; built-ins are Explore (read-only), Plan (plan mode research), and general-purpose.
  5. When not to: tasks needing multi-turn back-and-forth (every dispatch re-explains), phases that share heavy context, and one-line fixes where dispatch plus summary costs more than the work. Follow-up: subagent versus /compact — one keeps content out of the window, the other compresses it afterward; the former is cheaper.

  分析过程 · 先想清楚再作答

  1. 题眼是「解决了什么问题」——答案是保护主会话的上下文窗口，而不是「并行」或「专业化」这些附带好处。第二问是常见误区，第三问考边界感。
  2. 推导：查资料、审代码这类任务的特征是「读很多、留很少」——读三十个文件只为一段结论。放在主会话里做，三十个文件全进窗口，真正的实现反而没地方放。subagent 拥有独立的上下文窗口，读完只把总结带回来，主会话只付总结的成本。
  3. 第二问：看不到。subagent 起步时只有系统提示、你派给它的任务描述、CLAUDE.md、git 状态快照；主会话的历史、你之前读过的文件、之前加载的 skill 都不在。这是限制也是优点：一个没有「刚写完这段代码」记忆的审查者更容易挑出毛病，D5 的对抗式审查就靠这个性质。
  4. 配置：.claude/agents/<name>.md，frontmatter 的 tools 限定它能用什么（审查者不给 Edit）、model 可以配更便宜或更强的模型；内置的 Explore 只读、Plan 用于计划模式、general-purpose 全能。
  5. 不该用的场景：需要多轮来回讨论的活（每次派出去都要重新交代）、几个阶段要共享大量上下文的活、一句话就能改完的活（交代 + 总结的开销大于任务本身）。可预期的追问：subagent 与 /compact 的关系——一个是不让东西进窗口，一个是进了以后压缩，前者更省。

  Key points

  • Solves the main window being flooded by read-heavy, keep-little tasks; a subagent has its own window and returns a summary
  • It does not see the main history — only the task, CLAUDE.md, and a git snapshot — which makes its review more objective
  • tools restricts permissions, model picks the model; built-ins are Explore, Plan, general-purpose
  • Avoid for multi-turn discussion, heavy shared context across phases, and one-line fixes

  答题要点

  • 解决的是主会话上下文被「读很多留很少」的任务撑满；subagent 独立窗口，只带回总结
  • 看不到主会话历史，只有任务描述、CLAUDE.md、git 快照；因此审查更客观
  • tools 限定权限、model 选模型；内置 Explore / Plan / general-purpose
  • 不该用：多轮讨论、多阶段共享上下文、一句话能改完的小活

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