Interview Bank

From Frontend Engineer to Agent Engineer in 30 Days

D15 A Tour of Multi-Agent Patterns (Router/Supervisor, Planner-Executor, Critic, Swarm, Blackboard) and When Not to Use Them; Getting Started With LangGraph

• When should you not introduce a multi-agent system? Give operational criteria, not it depends.什么情况下不应该引入多 Agent 系统？请给出可操作的判据，而不是「视情况而定」。

  Common in ChinaCommon overseasDeep dive#multi-agent#architecture#trade-offs

  How to reason about it · think before answering

  1. This is the highest-signal question in the set because it is asked in reverse. Most candidates keep selling how powerful multi-agent is, while the interviewer is looking for someone who will say no — on a real team, blocking one unnecessary architecture upgrade is worth more than implementing three patterns.
  2. Lead with the default: do not split. Then give three criteria, any one of which justifies splitting — the system prompt contains mutually exclusive behavioural requirements (strictly enforce refund rules while also warmly retaining the customer; these are not hard to write, they are impossible to optimise together); the tool count exceeds what the model picks reliably (roughly eight as a rule of thumb, and the first response to crossing it is consolidating tools, not splitting agents); or one step needs its own failure and retry semantics. None of the three, and a single agent with a few tools is enough.
  3. Then name the most common bad split: treating a prompt problem as an architecture problem. Quality is poor, so we split into three agents — but nine times out of ten poor quality comes from vague prompts, tool descriptions that interfere with each other, or irrelevant history in the context. All three survive the split and are now harder to find. Splitting fixes conflicting responsibilities, not weak capability.
  4. Add two scenarios that clearly should not split: latency-sensitive interactions, where each extra hop is another model round trip and voice or realtime completion becomes unusable; and read-only lookup flows, where a support assistant with three or four tools gains no accuracy from splitting and simply triples the bill.
  5. Then offer an executable verification path, which earns points: keep the single-agent version as a baseline for any split and A/B both against the same golden set, comparing accuracy, per-conversation cost and latency together. An architecture upgrade with no baseline is a refactor with no evidence.
  6. Expect: what if your manager insists on multi-agent? Frame it as a reversible experiment — make the one cut you are most confident in (usually the conflicting-rules criterion), keep the baseline, and bring data in two weeks. That answer shows technical judgement and a way to disagree without stonewalling.

  分析过程 · 先想清楚再作答

  1. 这是本组最有区分度的题，因为它反着问。绝大多数候选人会顺着「多 Agent 很强大」讲下去，而面试官问这题正是想找那个会说不的人——**在真实团队里，拦住一次不必要的架构升级，价值高于实现三个模式**。
  2. 先给结论式的默认值：默认答案是不拆。然后给三条判据，命中任意一条才拆——一是单个 Agent 的系统提示词里出现了互斥的行为要求（既要严格核对退款规则又要热情挽留，这两条不是难写，是不可能同时最优）；二是工具数量超过模型能稳定选对的规模（经验线大约八个，超线的第一反应是合并工具而不是拆 Agent）；三是某一步需要独立的失败与重试语义。三条都不命中，单 Agent 加几个工具就够。
  3. 接着点名最常见的错拆：把提示词问题当成架构问题。「回答质量不好，所以拆成三个 Agent」——质量差有九成来自提示词含糊、工具描述互相干扰、上下文塞了无关历史，这三样拆完一样存在，只是分散到三个地方更难查。**拆 Agent 解决的是职责冲突，不是能力不足。**
  4. 再补两类明确不该拆的场景：一是低延迟要求的场景，多一跳就多一次模型往返，对语音或实时补全这类交互直接不可用；二是只读的简单查询链路，三五个工具的客服助手拆了只是把一次调用变成三次，准确率不会涨、账单会涨。
  5. 然后给一条可执行的验证路径，这是加分项：任何拆分都先留住单 Agent 版本当对照基线，用同一批标准样本集跑 A/B，同时比准确率、每次对话成本和延迟。**拿不出对照基线的架构升级，等于没有证据的重构。**
  6. 可以预期的追问：那如果老板就是要求上多 Agent 呢？答：那就把它当成一个可回退的实验来做——先按判据拆最有把握的那一刀（通常是互斥规则那一条），保留基线，两周后拿数据说话。这个回答同时展示了技术判断和沟通方式，比硬顶或硬上都好。

  Key points

  • Default to not splitting; split only if one of three criteria holds: mutually exclusive prompt requirements, tool count past the roughly-eight warning line, or a step needing its own failure and retry semantics
  • Too many tools should first trigger tool consolidation and tighter descriptions; splitting agents is the second response
  • The most common bad split is treating a prompt problem as an architecture problem — vague prompts, interfering tool descriptions and irrelevant history all survive the split
  • Clear do-not-split cases: latency-sensitive interactions where every hop adds a model round trip, and read-only lookup flows where accuracy does not move but the bill does
  • Always keep the single-agent version as a baseline and compare accuracy, cost and latency on the same golden set
  • Say the costs out loud: latency multiplies with steps, spend roughly triples, and debugging now spans routing plus state merging

  答题要点

  • 默认答案是不拆；三条判据命中任意一条才拆：提示词有互斥要求、工具超过约八个的告警线、某一步需要独立的失败与重试语义
  • 工具太多的第一反应是合并工具与收敛描述，拆 Agent 是第二反应
  • 最常见的错拆是把提示词问题当架构问题——质量差多半来自提示词含糊、工具描述干扰、上下文塞了无关历史，拆完这三样照旧存在
  • 明确不该拆：低延迟交互（每多一跳就多一次模型往返）、只读的简单查询链路（准确率不涨、账单涨）
  • 任何拆分都要留单 Agent 版本当对照基线，用同一批标准样本集比准确率、成本和延迟
  • 代价要说出口：延迟按步数乘倍数、成本约三倍、调试要同时排查路由与状态合并

D23 MCP and Skills: the Protocol, Server/Client, How It Differs From Function Calling; a Tour of the Claude Agent SDK

• When should you reach for MCP instead of plain function calling, and what does it cost when you shouldn't?什么场景下应该考虑用 MCP，而不是直接写 function calling？不该用的时候硬上会付出什么代价？

  Common in ChinaCommon overseasIntermediate#mcp#architecture#trade-offs

  How to reason about it · think before answering

  1. The hinge is the second half. Answering only 'MCP is more standard and decoupled' is like saying 'microservices are more decoupled' — true-sounding but with no criterion, and the interviewer will immediately ask whether you turned every tool into an MCP server.
  2. Give three actionable criteria: the capability must be reused by more than one host, owned by another team or a third party, or added and removed without changing host code. Any one of them justifies MCP; none of them means write a local function. Making 'no' the default answer shows more engineering judgment than the criteria themselves.
  3. Attach a reason to each: multi-host reuse turns N times M into N plus M; external ownership makes the process boundary the responsibility boundary, so their change is not your release; hot-swapping demotes adding an internal tool from a deployment to a config change.
  4. Then state the costs honestly, which is where shipped experience shows: another process to keep alive, another handshake with its own timeouts and reconnects, and a debugging path that went from one hop to three — a tool that never got called might mean the model did not pick it, the schema lost fields in translation, or the server never started. On stdio you also own reaping the child process.
  5. One more point that is easy to miss and scores well: MCP does not change your cost structure. Tool descriptions still enter the context every turn, and more tools still degrade tool selection. The rule that you should consolidate tools past a certain count survives MCP unchanged — arguably it matters more, because now other people can add entries to your tool list.
  6. Expect the follow-up: so internal tools never go through MCP? Not quite. If you want the same capability available to an IDE assistant and an ops bot as well, the first criterion is met even though you own the code.

  分析过程 · 先想清楚再作答

  1. 题眼在后半句。只会说「MCP 更标准更解耦」的人，等于说「微服务更解耦」——听起来对，但没有判据，面试官会立刻追问「那你们所有工具都做成 MCP server 了吗」。
  2. 先给判据，而且要是可执行的三条：能力要被多个宿主复用、能力由另一个团队或第三方维护、需要不改宿主代码就能增删能力。命中任意一条才考虑，**一条都不命中就直接写本地函数**——把默认答案摆成「不上」，这条比三条判据本身更能体现工程判断。
  3. 每条判据配一句为什么：多宿主复用把 N 乘 M 变成 N 加 M；别人维护时进程边界就是责任边界，他们改他们的、你不用发版；热插拔让加一个内部工具从一次发布降级成一次配置变更。
  4. 然后老实说代价，这是区分「用过」和「读过」的地方：多一个进程要保活、多一次握手要处理超时与重连、排障链路从一段变三段——工具没被调用，现在可能是模型没选、可能是 schema 翻译时丢了字段、也可能是 server 压根没起来。stdio 的子进程还要你自己回收，否则留孤儿进程。
  5. 还有一条容易被忽略但很加分：MCP 不改变你的成本结构。工具描述照样每轮都进上下文，工具多了照样会让模型选错——D5 那条「工具超过一定数量就该合并描述」在接了 MCP 之后一字不变，甚至更需要，因为现在别人可以往你的工具列表里塞东西。
  6. 可以预期的追问：那内部工具一律不上 MCP 吗？不是。有一类值得例外——你希望它能被 IDE 里的助手和运维机器人一起用，那第一条判据就命中了，即使它是你自己维护的。

  Key points

  • Three criteria, any one justifies MCP: reuse across hosts, ownership by another team, or add/remove without touching host code
  • The default is no — if none of the three apply, a local function is the better engineering decision
  • Costs: another process to supervise, another handshake with timeouts, and a debug path that grows from one hop to three
  • MCP does not change your cost structure: descriptions still enter context every turn and too many tools still hurt selection
  • Once third-party capabilities are attached, your tool list is no longer fully under your control, which is itself a design problem

  答题要点

  • 三条判据，命中任意一条才考虑 MCP：多宿主复用、由他人维护、需要不改代码增删能力
  • 默认答案是不上：三条都不命中就直接写本地函数，这是更好的工程决策
  • 代价是多一个进程要保活、多一次握手要处理超时、排障从一段链路变成三段
  • MCP 不改变成本结构：工具描述照样每轮进上下文，工具过多照样会让模型选错，该合并还是要合并
  • 第三方能力接进来之后，工具列表不再完全由你掌控，这本身就是需要设计的一件事