Meta mcp builder

MCP Server Development Guide

Create MCP servers that enable LLMs to interact with external services.

Overview

MCP (Model Context Protocol) servers expose tools that AI agents can use. Quality is measured by how well they enable agents to accomplish real tasks.

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Quick Start

1. Choose Stack

Recommended: TypeScript with MCP SDK

• High-quality SDK support
• Good compatibility across environments
• Strong type safety

Alternative: Python with FastMCP

• Good for Python-heavy workflows

2. Project Structure

my-mcp-server/
├── src/
│ ├── index.ts # Entry point
│ ├── tools/ # Tool implementations
│ │ ├── search.ts
│ │ └── create.ts
│ └── utils/ # Shared utilities
│ ├── api-client.ts
│ └── error-handler.ts
├── package.json
├── tsconfig.json
└── README.md

---

Tool Design Principles

1. Clear Naming

// ✅ Good - action-oriented, prefixed
'github_create_issue'
'github_list_repos'
'slack_send_message'

// ❌ Avoid - vague
'process'
'handle'
'do_thing'

2. Concise Descriptions

{
 name: 'github_search_issues',
 description: 'Search GitHub issues by query, state, and labels. Returns issue title, number, and URL.',
}

3. Typed Parameters

import { z } from 'zod';

const searchIssuesSchema = z.object({
 query: z.string().describe('Search query string'),
 state: z.enum(['open', 'closed', 'all']).default('open'),
 labels: z.array(z.string()).optional().describe('Filter by labels'),
 limit: z.number().min(1).max(100).default(10),
});

4. Actionable Errors

// ❌ Bad
throw new Error('Failed');

// ✅ Good
throw new Error(
 `GitHub API rate limit exceeded. ` +
 `Resets at ${resetTime}. ` +
 `Try again later or authenticate for higher limits.`
);

---

Implementation Pattern

Basic Tool Structure

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { z } from 'zod';

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

// Define tool
server.tool(
 'service_action',
 'Description of what this tool does and when to use it',
 {
 param1: z.string().describe('What this param is for'),
 param2: z.number().optional().describe('Optional param'),
 },
 async ({ param1, param2 }) => {
 // Implementation
 const result = await performAction(param1, param2);

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

Tool Annotations

server.tool(
 'delete_item',
 'Delete an item permanently',
 { id: z.string() },
 async ({ id }) => { /* ... */ },
 {
 annotations: {
 readOnlyHint: false, // Modifies data
 destructiveHint: true, // Cannot be undone
 idempotentHint: true, // Safe to retry
 openWorldHint: false, // Closed set of operations
 },
 }
);

---

Best Practices

API Coverage vs Workflow Tools

Approach	When to Use
full API coverage	Agent needs flexibility to compose operations
Workflow tools	Specific task needs multi-step automation

Default: Start with full API coverage, add workflow tools for common patterns.

Response Formatting

// Return structured data
return {
 content: [{
 type: 'text',
 text: JSON.stringify({
 success: true,
 data: results,
 metadata: { count: results.length },
 }, null, 2),
 }],
};

Pagination Support

const listItemsSchema = z.object({
 limit: z.number().min(1).max(100).default(20),
 cursor: z.string().optional().describe('Pagination cursor from previous response'),
});

// Return cursor in response
return {
 items: results,
 nextCursor: hasMore ? lastId : null,
};

---

Testing

1. Build Check

npm run build # Must pass without errors

2. Test with Inspector

npx @modelcontextprotocol/inspector

3. Test Each Tool

• Valid inputs → expected output
• Invalid inputs → helpful error
• Edge cases → graceful handling

---

Quality Checklist

• All tools have clear, descriptive names
• All parameters have descriptions
• Error messages are actionable
• Pagination for list operations
• No hardcoded credentials
• TypeScript types for all inputs/outputs
• README documents all tools
• Examples provided for complex tools

---

Common Patterns

Authentication

const apiKey = process.env.SERVICE_API_KEY;
if (!apiKey) {
 throw new Error('SERVICE_API_KEY environment variable required');
}

Rate Limiting

import { RateLimiter } from 'limiter';

const limiter = new RateLimiter({
 tokensPerInterval: 100,
 interval: 'minute',
});

async function callApi() {
 await limiter.removeTokens(1);
 // Make API call
}

Caching

const cache = new Map<string, { data: any; expiry: number }>();

async function getCached(key: string, fetcher: () => Promise<any>) {
 const cached = cache.get(key);
 if (cached && cached.expiry > Date.now()) {
 return cached.data;
 }
 const data = await fetcher();
 cache.set(key, { data, expiry: Date.now() + 60000 });
 return data;
}

---

Resources

• MCP Specification: https://modelcontextprotocol.io
• TypeScript SDK: https://github.com/modelcontextprotocol/typescript-sdk
• Python SDK: https://github.com/modelcontextprotocol/python-sdk