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
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:
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 }],
};
}
});
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.