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

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

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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