Interview Bank

Context Engineering in 5 Days

D1 Context Is the Scarcest Resource: the Window, Attention Decay, and Cost — From Prompt Engineering to Context Engineering

• Where is the line between prompt engineering and context engineering, and when do you switch?提示词工程和上下文工程的分界在哪？什么时候该从前者切换到后者？

  Common in ChinaCommon overseasIntermediate#prompt-engineering#context-engineering#scoping

  How to reason about it · think before answering

  1. The trap is answering that context engineering is just prompt engineering leveled up. Interviewers want a rule they can apply to classify a live problem.
  2. Start with the object of each. Prompt engineering shapes content: how to phrase one instruction precisely. Context engineering allocates budget: how much of the window each part gets and when to drop things. One optimizes inside a single call, the other manages state across turns.
  3. Then give a symptom-based test. Wrong once but right after rephrasing means a prompt problem. Fine for five turns and violating the original constraints by turn twenty means a context problem. Retrieving the data and then claiming it does not exist is also a context problem: the information is in the window but buried.
  4. Conclusion: you switch not when the prompt is good enough, but when the cause moves from single-turn phrasing to multi-turn accumulation. Adding tools, adding retrieval, or running long sessions each trigger the switch.
  5. Expect the follow-up: does context engineering subsume prompt engineering? The system prompt is one of the four parts, so prompt engineering is a subproblem, but it cannot touch tool definitions, history, or tool results.

  分析过程 · 先想清楚再作答

  1. 这题最容易答成「上下文工程是提示词工程的升级版」，那是营销话术。面试官想听的是一条能当场用来分类问题的判据。
  2. 怎么拆：先给对象的差别。提示词工程处理的是内容——一段话怎么写才准确；上下文工程处理的是预算分配——整只箱子里各块占多少、什么时候该扔。前者是单次调用内的优化，后者是跨多轮的状态管理。
  3. 再给一条现场可用的分类法，用症状反推：同一个问题问一次答错、换个说法就对，是提示词问题；前五轮正常、第二十轮开始违反最初约束，是上下文问题；明明查到了数据模型却说没有，也是上下文问题——信息在窗口里，只是被淹没了。
  4. 结论：切换的时机不是「提示词写得够好了」，而是「问题的成因从单次表达变成了多轮累积」。加了工具、加了检索、开始多轮长跑，这三件事任何一件发生，都意味着该切换了。
  5. 可预期的追问：那上下文工程包含提示词工程吗？答：系统提示是上下文四块里的一块，所以提示词工程是上下文工程的一个子问题，但它解决不了另外三块——工具定义、历史和工具结果都不是靠把话写好能管住的。

  Key points

  • Prompt engineering shapes content; context engineering allocates budget across turns.
  • Classify by symptom: fixed by rephrasing is a prompt issue; drifting after many turns is a context issue; retrieved but reported missing is also a context issue.
  • Switch when the cause moves from single-turn phrasing to multi-turn accumulation, typically after adding tools, retrieval, or long-running sessions.
  • The system prompt is one of four parts, so good phrasing alone cannot control the other three.

  答题要点

  • 提示词工程处理内容，上下文工程处理预算分配；一个在单次调用内，一个跨多轮。
  • 症状分类法：换个说法就对是提示词问题；跑久了开始违反约束是上下文问题；查到了却说没有也是上下文问题。
  • 切换时机是问题成因从单次表达变成多轮累积，通常发生在加工具、加检索、开始长跑之后。
  • 系统提示只是上下文四块之一，所以写好提示词管不住另外三块。