MCP Protocol

Build and connect Model Context Protocol servers to Claude Code.

The Model Context Protocol (MCP) is an open protocol for connecting AI models to external tools and data sources. Claude Code implements MCP as both a client (connecting to MCP servers) and uses MCP-compatible patterns internally.

MCP concepts

Concept	Description
Server	A process that exposes tools, resources, and prompts
Tool	An action the model can invoke (e.g., query a database)
Resource	Data the model can read (e.g., a file, a DB row)
Prompt	A reusable prompt template
Transport	How the server communicates: stdio or HTTP

Building an MCP server

Create an MCP server using the official MCP SDK:

npm install @modelcontextprotocol/sdk

server.ts

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
  CallToolRequestSchema,
  ListToolsRequestSchema,
} from "@modelcontextprotocol/sdk/types.js";

const server = new Server(
  { name: "my-mcp-server", version: "1.0.0" },
  { capabilities: { tools: {} } }
);

server.setRequestHandler(ListToolsRequestSchema, async () => ({
  tools: [
    {
      name: "query_database",
      description: "Query the application database",
      inputSchema: {
        type: "object",
        properties: {
          sql: { type: "string", description: "SQL query to execute" },
        },
        required: ["sql"],
      },
    },
  ],
}));

server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "query_database") {
    const { sql } = request.params.arguments as { sql: string };
    // Execute query and return results
    return { content: [{ type: "text", text: JSON.stringify(results) }] };
  }
});

const transport = new StdioServerTransport();
await server.connect(transport);

Connecting your server to Claude Code

Add the server via /mcp:

> /mcp

Select “Add server” and provide:

• Type: stdio
• Command: node server.js (or however you launch the server)

Exposing resources

Resources let Claude read data from your server:

import { ListResourcesRequestSchema, ReadResourceRequestSchema } from "@modelcontextprotocol/sdk/types.js";

server.setRequestHandler(ListResourcesRequestSchema, async () => ({
  resources: [
    {
      uri: "db://schema",
      name: "Database schema",
      mimeType: "text/plain",
    },
  ],
}));

server.setRequestHandler(ReadResourceRequestSchema, async (request) => {
  if (request.params.uri === "db://schema") {
    return {
      contents: [{ uri: "db://schema", mimeType: "text/plain", text: schemaText }],
    };
  }
});

Claude Code accesses resources via ListMcpResourcesTool and ReadMcpResourceTool.

Authentication

For HTTP-based MCP servers, Claude Code supports the McpAuthTool for authentication flows. For local stdio servers, no authentication is needed — the server runs as a local process.

The MCP SDK handles protocol framing, serialization, and transport. You only need to implement the handlers for your specific tools and resources.

For more on connecting servers, see MCP Servers.