Prompt 11: MCP Client/Server Integration

Context

You are working in /workspaces/claude-code. The CLI has built-in MCP (Model Context Protocol) support:

MCP Client — connects to external MCP servers (tools, resources)
MCP Server — exposes Claude Code itself as an MCP server

MCP lets the CLI use tools provided by external servers and lets other clients use Claude Code as a tool provider.

Key Files

src/services/mcp/ — MCP client implementation
src/services/mcp/types.ts — MCP config types
src/entrypoints/mcp.ts — MCP server mode entrypoint
src/tools/MCPTool/ — Tool that calls MCP servers
src/tools/ListMcpResourcesTool/ — Lists MCP resources
src/tools/ReadMcpResourceTool/ — Reads MCP resources
src/tools/McpAuthTool/ — MCP server authentication
mcp-server/ — Standalone MCP server sub-project (from Prompt 04)

Task

Part A: Understand MCP client architecture

Read src/services/mcp/ directory:

How are MCP servers discovered? (.mcp.json config file?)
How are MCP server connections established? (stdio, HTTP, SSE?)
How are MCP tools registered and made available?
What is the ScopedMcpServerConfig type?

Part B: Understand MCP config format

Search for .mcp.json or MCP config loading code. Document:

Where does the config file live? (~/.claude/.mcp.json? project root?)
What's the config schema? (server name, command, args, env?)
How are multiple servers configured?

Example config you might find:

{
  "mcpServers": {
    "my-server": {
      "command": "node",
      "args": ["path/to/server.js"],
      "env": {}
    }
  }
}

Part C: Verify MCP SDK integration

The project uses @modelcontextprotocol/sdk (^1.12.1). Check:

Is it installed in node_modules/?
Does the import work: import { Client } from '@modelcontextprotocol/sdk/client/index.js'
Are there version compatibility issues?

Part D: Test MCP client with our own server

Create a test that:

Starts the mcp-server/ we fixed in Prompt 04 as a child process
Connects to it via stdio using the MCP client from src/services/mcp/
Lists available tools
Calls one tool (e.g., list_files or search_code)

Create scripts/test-mcp.ts:

// scripts/test-mcp.ts
// Test MCP client/server roundtrip
// Usage: bun scripts/test-mcp.ts

import './src/shims/preload.js'

// TODO: 
// 1. Spawn mcp-server as a child process (stdio transport)
// 2. Create MCP client from src/services/mcp/
// 3. Connect client to server
// 4. List tools
// 5. Call a tool
// 6. Print results

Part E: Test MCP server mode

The CLI can run as an MCP server itself (src/entrypoints/mcp.ts). Read this file and verify:

What tools does it expose?
What resources does it provide?
Can it be started with bun src/entrypoints/mcp.ts?

Part F: Create sample MCP config

Create a .mcp.json in the project root (or wherever the app looks for it) that configures the local MCP server:

{
  "mcpServers": {
    "claude-code-explorer": {
      "command": "node",
      "args": ["mcp-server/dist/index.js"],
      "env": {
        "CLAUDE_CODE_SRC_ROOT": "./src"
      }
    }
  }
}

Verification

MCP client code in src/services/mcp/ loads without errors
MCP server mode (src/entrypoints/mcp.ts) starts without crashing
A roundtrip test (client → server → response) works
.mcp.json config file is created and parseable

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