13 — Quiz: build your own harness

Pick an answer. The quiz checks it and shows the explanation.

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1. Your SDK script runs a query. Which component actually runs your lookup_service handler when Claude asks for it?

a) the model, on Anthropic's servers

b) the SDK, inside your process, through the in-process MCP server

c) a separate MCP server process that the SDK starts

d) your shell, as a Bash command

b — the model only asks for the tool. createSdkMcpServer() runs the server inside your application, and the SDK calls the handler there.

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2. You print every message from query(). Which order shows one tool call and a final answer?

a) result, assistant, user, system/init

b) assistant, system/init, result, user

c) system/init, user with tool_use, assistant with tool_result, result

d) system/init, assistant with tool_use, user with tool_result, assistant with text, result

d — the init message comes first. Claude's tool request arrives as an assistant message, the tool's output goes back as a user message, and result ends the loop.

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3. You register a server as mcpServers: { inventory: server } with a tool named lookup_service. What do you put in allowedTools?

a) lookup_service

b) inventory.lookup_service

c) mcp__inventory__lookup_service

d) mcp__*

c — MCP tools are named mcp__<key in mcpServers>__<tool name>. An unanchored mcp__* allow rule is ignored.

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4. A teammate sets allowedTools: ["Read"] and permissionMode: "bypassPermissions", and expects Claude to only read. What happens when Claude calls Bash?

a) it runs: unlisted tools fall through to the mode, and bypass approves them

b) it's denied, because Bash isn't in allowedTools

c) canUseTool is asked

d) the SDK refuses to start with this combination

a — allowedTools pre-approves the tools it lists. It doesn't restrict the others. To block a tool, use disallowedTools or leave it out of tools.

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5. You want Claude to see no built-in tools at all, only your MCP tool. Which option does that?

a) allowedTools: ["mcp__inventory__lookup_service"]

b) permissionMode: "plan"

c) settingSources: []

d) tools: []

d — tools: [] removes every built-in from Claude's context, and MCP tools stay. allowedTools only decides what runs without asking.

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6. Your harness has no settingSources option. Your project has a CLAUDE.md and a .claude/settings.json with hooks. What does the SDK load?

a) nothing from disk: the SDK only uses what you pass in code

b) only CLAUDE.md

c) both, plus user and local settings, like the Claude Code CLI

d) only managed policy settings

c — when settingSources is left out, query() reads user, project and local settings, CLAUDE.md files and .claude/ content. Pass settingSources: [] to turn that off.

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7. Your tool deletes old log files, and you mark it readOnlyHint: true. What does the hint change?

a) the SDK blocks any write the handler tries

b) nothing about what the handler does: it's metadata, not enforcement

c) the tool can only be called in plan mode

d) the tool needs no entry in allowedTools

b — annotations describe the tool. They let Claude batch read-only calls, but the handler's code decides what it really does, so keep the hint accurate.

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8. In dontAsk mode, Claude calls a tool that no allow rule covers and that needs approval. What happens?

a) your canUseTool callback decides

b) it runs, because dontAsk never prompts

c) the session stops with an error

d) the call is denied, without calling canUseTool

d — dontAsk turns every call that would prompt into a deny, and the canUseTool step is skipped.

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9. You list mcp__inventory__lookup_service in both allowedTools and disallowedTools. What happens when Claude tries the tool?

a) it runs, because allow rules are checked first

b) it's denied: deny rules are checked before allow rules

c) canUseTool decides

d) the last option you wrote wins

b — the SDK checks hooks, then deny rules, then ask rules, the mode, and allow rules last. A deny that matches ends it, the same rule as in Chapter 04.

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