How to Build MCP Servers for Claude Code (Complete Tutorial)

The Model Context Protocol (MCP) is what makes Claude Code extensible. It's the standard that lets you give Claude access to your databases, APIs, file systems, and any custom tool you can imagine.

Building an MCP server is surprisingly straightforward. Let's build one from scratch.

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What is MCP?

MCP is a protocol that standardizes how AI models communicate with external tools. Think of it as USB for AI — a universal connector that lets any AI model use any tool.

An MCP server:

1. Defines available tools (what can Claude do?)

2. Handles tool calls (Claude says "query the database," the server executes it)

3. Returns results (sends data back to Claude)

---

Setting Up Your First MCP Server

Step 1: Project Setup

mkdir my-mcp-server
cd my-mcp-server
npm init -y
npm install @modelcontextprotocol/sdk zod
npm install -D typescript @types/node tsx
npx tsc --init

Step 2: Basic Server Structure

// src/index.ts
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { z } from 'zod';

const server = new McpServer({
  name: 'my-custom-tools',
  version: '1.0.0',
});

// Define a simple tool
server.tool(
  'greet',
  'Greet a user by name',
  {
    name: z.string().describe('The name to greet'),
  },
  async ({ name }) => ({
    content: [
      {
        type: 'text',
        text: `Hello, ${name}! Welcome to my MCP server.`,
      },
    ],
  })
);

// Start the server
async function main() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
}

main().catch(console.error);

Step 3: Register with Claude Code

// In your project's .claude/settings.json or CLAUDE.md:
// Add the MCP server configuration
{
  "mcpServers": {
    "my-tools": {
      "command": "npx",
      "args": ["tsx", "/path/to/my-mcp-server/src/index.ts"]
    }
  }
}

---

Building a Database MCP Server

The most common use case: giving Claude access to your database.

// src/database-server.ts
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { z } from 'zod';
import { Pool } from 'pg';

const pool = new Pool({
  connectionString: process.env.DATABASE_URL,
});

const server = new McpServer({
  name: 'database-tools',
  version: '1.0.0',
});

// Read-only query tool
server.tool(
  'query_database',
  'Execute a read-only SQL query against the database',
  {
    sql: z.string().describe('The SQL SELECT query to execute'),
  },
  async ({ sql }) => {
    // Safety: only allow SELECT queries
    if (!sql.trim().toUpperCase().startsWith('SELECT')) {
      return {
        content: [{
          type: 'text',
          text: 'Error: Only SELECT queries are allowed.',
        }],
        isError: true,
      };
    }

    try {
      const result = await pool.query(sql);
      return {
        content: [{
          type: 'text',
          text: JSON.stringify(result.rows, null, 2),
        }],
      };
    } catch (error) {
      return {
        content: [{
          type: 'text',
          text: `Query error: ${error.message}`,
        }],
        isError: true,
      };
    }
  }
);

// Table schema tool
server.tool(
  'list_tables',
  'List all tables in the database with their columns',
  {},
  async () => {
    const result = await pool.query(`
      SELECT table_name, column_name, data_type
      FROM information_schema.columns
      WHERE table_schema = 'public'
      ORDER BY table_name, ordinal_position
    `);
    return {
      content: [{
        type: 'text',
        text: JSON.stringify(result.rows, null, 2),
      }],
    };
  }
);

---

Building an API Integration Server

// src/api-server.ts
server.tool(
  'search_github',
  'Search GitHub repositories',
  {
    query: z.string().describe('Search query for repositories'),
    language: z.string().optional().describe('Filter by programming language'),
  },
  async ({ query, language }) => {
    const params = new URLSearchParams({
      q: language ? `${query} language:${language}` : query,
      sort: 'stars',
      order: 'desc',
    });

    const response = await fetch(
      `https://api.github.com/search/repositories?${params}`,
      { headers: { 'Accept': 'application/vnd.github.v3+json' } }
    );

    const data = await response.json();
    const repos = data.items.slice(0, 10).map(repo => ({
      name: repo.full_name,
      description: repo.description,
      stars: repo.stargazers_count,
      url: repo.html_url,
    }));

    return {
      content: [{
        type: 'text',
        text: JSON.stringify(repos, null, 2),
      }],
    };
  }
);

---

Security Best Practices

1. Never allow write operations without confirmation — read-only by default

2. Validate and sanitize all inputs — use Zod schemas for type safety

3. Limit query scope — restrict database access to specific schemas/tables

4. Log all tool calls — audit trail for debugging and security

5. Use environment variables for credentials — never hardcode secrets

6. Rate limit tool calls — prevent runaway agent behavior

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People Also Ask

What languages can MCP servers be built in?

The official SDK supports TypeScript/JavaScript and Python. Community SDKs exist for Go, Rust, and other languages.

Can MCP servers run remotely?

Yes — MCP supports both stdio (local) and HTTP/SSE (remote) transports. Remote servers can run on any cloud provider.

How many tools can an MCP server expose?

There's no hard limit, but keep it focused. A server with 5-10 well-defined tools is better than one with 50 vague tools. Claude needs to understand what each tool does to use it effectively.

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Originally published at wowhow.cloud