Build Custom MCP Servers: Complete Beginner Guide 2025

const server = {
name: "company-crm", version: "1.0.0", description: "Access customer data from Company CRM" };

const tools = [
{ name: "get_customer", description: "Fetch customer details by ID", input_schema: { type: "object", properties: { customer_id: { type: "string" } } } }, { name: "search_customers", description: "Search customers by name or email", input_schema: { type: "object", properties: { query: { type: "string" } } } } ];

async function executeGetCustomer(customer_id) {
// Call your CRM API const response = await fetch(https://crm.company.com/api/customers/${customer_id}, { headers: { 'Authorization': Bearer ${process.env.CRM_API_KEY} } }); const data = await response.json(); return data; }

mkdir mcp-server-companywiki
cd mcp-server-companywiki npm init -y npm install @anthropic-ai/mcp-sdk

import { MCPServer } from '@anthropic-ai/mcp-sdk';
const server = new MCPServer({ name: 'company-wiki', version: '1.0.0', description: 'Search and access company wiki articles' });
// Define what actions Claude can take server.addTool({ name: 'search_wiki', description: 'Search wiki articles by keyword', input_schema: { type: 'object', properties: { query: { type: 'string', description: 'Search query' } }, required: ['query'] }, handler: async ({ query }) => { // Call your wiki's search API const response = await fetch(
https://wiki.company.com/api/search?q=${encodeURIComponent(query)},
{ headers: { 'Authorization': Bearer ${process.env.WIKI_API_TOKEN} } } );
const results = await response.json();
// Return formatted results return { content: [ { type: 'text', text: JSON.stringify(results, null, 2) } ] }; } });
server.addTool({ name: 'get_article', description: 'Get full content of a wiki article by ID', input_schema: { type: 'object', properties: { article_id: { type: 'string', description: 'Wiki article ID' } }, required: ['article_id'] }, handler: async ({ article_id }) => { const response = await fetch(
https://wiki.company.com/api/articles/${article_id},
{ headers: { 'Authorization': Bearer ${process.env.WIKI_API_TOKEN} } } );
const article = await response.json();
return { content: [ { type: 'text', text: # ${article.title}\n\n${article.content} } ] }; } });
// Start the server server.start();

npm run build
node dist/index.js

{
"mcpServers": { "company-wiki": { "command": "node", "args": ["/path/to/mcp-server-companywiki/dist/index.js"], "env": { "WIKI_API_TOKEN": "your-api-token-here" } } } }

import { Client } from 'pg';
server.addTool({ name: 'query_sales_data', description: 'Run SQL query against sales database', input_schema: { type: 'object', properties: { query: { type: 'string' } }, required: ['query'] }, handler: async ({ query }) => { const client = new Client({ connectionString: process.env.DATABASE_URL });
await client.connect(); const result = await client.query(query); await client.end();
return { content: [{ type: 'text', text: JSON.stringify(result.rows, null, 2) }] }; } });

server.addTool({
name: 'get_inventory', description: 'Get current inventory levels', input_schema: { type: 'object', properties: { sku: { type: 'string', description: 'Product SKU (optional)' } } }, handler: async ({ sku }) => { const url = sku ? https://api.company.com/inventory/${sku} : 'https://api.company.com/inventory';
const response = await fetch(url, { headers: { 'X-API-Key': process.env.INVENTORY_API_KEY } });
const data = await response.json();
return { content: [{ type: 'text', text: JSON.stringify(data, null, 2) }] }; } });

import { readFile } from 'fs/promises';
import { join } from 'path';
server.addTool({ name: 'read_company_file', description: 'Read files from company shared drive', input_schema: { type: 'object', properties: { path: { type: 'string', description: 'File path relative to shared drive' } }, required: ['path'] }, handler: async ({ path }) => { const fullPath = join(process.env.SHARED_DRIVE_PATH, path); const content = await readFile(fullPath, 'utf-8');
return { content: [{ type: 'text', text: content }] }; } });

Start server
node dist/index.js
In another terminal, test with MCP client
npx @anthropic-ai/mcp-client \ --server "node dist/index.js" \ --tool search_wiki \ --input '{"query": "test"}'