Interview Bank

Mastering Claude: From Conversation to Claude Code in 5 Days

D1 Advanced Prompting and Claude's "Personality": System Prompt, XML Tags, Letting the Model Think First, Structured Output

• What belongs in a system prompt and what doesn't? If the model keeps ignoring one rule, what do you check first?system prompt 应该放什么、不该放什么？如果一条规则模型总是不遵守，你会先检查什么？

  Common in ChinaCommon overseasBasic#system-prompt#prompt-design

  How to reason about it · think before answering

  1. The question tests boundaries, not writing skill. Naming what to exclude, and why, is what separates a strong answer.
  2. Give the rule: the system prompt is a fixed premise resent on every request, so it holds only what is true for the whole conversation — role, constraints as prohibitions, output style. Anything that varies per turn belongs in the user message.
  3. Then the anti-patterns: obvious conventions, pasted API docs, and per-turn material dilute the important rules and also invalidate the prompt-cache prefix on every call.
  4. Debug order for an ignored rule: check length first and prune, then check for ambiguity or conflicting rules, and only then add emphasis. If the rule is a must-run action, move it to a deterministic gate instead of adding more words.
  5. Likely follow-up: can system go last? Possible but unwise — earlier instructions carry more weight and a moving prefix breaks caching.

  分析过程 · 先想清楚再作答

  1. 这题考的是「职责边界」而不是「会不会写」。答成「放角色和要求」是及格线，能说出「不该放什么」以及「为什么」才有区分度。
  2. 先给一条判据：system prompt 是每次请求都重发的固定前提，所以只放整场对话都成立的东西——角色、边界（禁止项）、输出风格；每次都变的（时间、用户名、本轮材料）放 user 消息。
  3. 再说反面：把模型本来就知道的常识（「写干净的代码」）、大段 API 文档、每轮都不一样的材料塞进 system，只会稀释真正重要的规则，还会让 prompt caching 的前缀每次都变。
  4. 「规则总是不遵守」的排查顺序：先看 system 是不是太长导致规则被淹没（删到不能再删），再看规则是否含糊或与别的规则冲突，最后才考虑加强调；如果是「每次必须执行」的动作，应该改成程序层面的门禁而不是继续加规则。
  5. 可预期的追问：system 放最后行不行？可以但不推荐——模型对靠前的指令更敏感，且会破坏缓存前缀。

  Key points

  • Include role, prohibitions, and output style — premises that hold for the whole conversation
  • Exclude volatile facts, common sense the model already has, and long pasted docs
  • The system prompt is resent every request: longer means costlier and rules get buried
  • For an ignored rule: prune first, disambiguate second, emphasize last; must-run actions become deterministic gates

  答题要点

  • 放：角色、边界（写禁止项）、输出风格；整场对话都成立的固定前提
  • 不放：会变的信息（时间、用户名、本轮材料）、模型本来就知道的常识、大段文档
  • system 每次请求重发，越长越贵，也越容易让关键规则被淹没
  • 规则不被遵守先删再改再强调；「每次必须做」的动作改成程序门禁