MCP Server Development

Build Model Context Protocol servers that expose tools, resources, and prompts to AI coding agents.

When to Use

• Building a tool server for Copilot, Claude, or other MCP-compatible agents
• Exposing an API, database, or service as agent-callable tools
• Creating reusable prompt templates for agent workflows
• Providing file/resource access to agents through a standard protocol

Decision Tree

Need to expose capabilities to AI agents?
+- Read-only data access?
| - Use MCP Resources (URI-based, typed)
+- Execute actions / side effects?
| - Use MCP Tools (JSON Schema input, structured output)
+- Reusable prompt templates?
| - Use MCP Prompts (parameterized, multi-turn)
- Combine multiple?
 - Single MCP server with mixed capabilities

Architecture Overview

-------------- stdio/SSE --------------
| AI Agent | ------------- | MCP Server |
| (Copilot) | JSON-RPC 2.0 | (your code) |
-------------- ------+-------
 |
 -------------+-------------
 | | |
 Tools Resources Prompts
 (actions) (read data) (templates)

Quick Start: TypeScript

npm init -y
npm install @modelcontextprotocol/sdk zod

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-server",
 version: "1.0.0",
});

// Tool: execute actions
server.tool("greet", { name: z.string() }, async ({ name }) => ({
 content: [{ type: "text", text: `Hello, ${name}!` }],
}));

// Resource: read-only data
server.resource("config", "config://app", async () => ({
 contents: [{ uri: "config://app", text: JSON.stringify({ env: "prod" }) }],
}));

// Start server
const transport = new StdioServerTransport();
await server.connect(transport);

Quick Start: Python

pip install mcp

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("my-server")

@mcp.tool()
def greet(name: str) -> str:
 """Greet a user by name."""
 return f"Hello, {name}!"

@mcp.resource("config://app")
def get_config() -> str:
 """Read application configuration."""
 return '{"env": "prod"}'

# Run: python server.py

Core Rules

1. Transport Selection

Transport	Use When	Pros
stdio	Local tools, VS Code extensions	Simple, secure, no network
SSE	Remote servers, shared services	Network accessible, multi-client
Streamable HTTP	Production APIs	Scalable, stateless-friendly

2. Tool Design

• One tool, one action: Don't create God-tools that do everything
• Descriptive names: search-issues not doThing
• Typed inputs: Use JSON Schema / Zod / Pydantic for all parameters
• Structured output: Return { content: [{ type: "text", text: "..." }] }
• Error handling: Return isError: true with descriptive messages, don't throw

3. Resource Design

• URI scheme: Use descriptive schemes (db://, file://, config://)
• Typed content: Set mimeType on all resource contents
• Templates: Use URI templates for parameterized resources: db://users/{id}
• Pagination: For large collections, support cursor-based pagination

4. Security

• Validate all inputs: Never trust agent-provided data
• Least privilege: Only expose necessary capabilities
• No secrets in responses: Filter sensitive data before returning
• Rate limiting: Protect against excessive tool calls
• Audit logging: Log all tool invocations with parameters

5. Configuration for VS Code

Add to .vscode/mcp.json (or user settings):

{
 "servers": {
 "my-server": {
 "command": "node",
 "args": ["./dist/server.js"],
 "env": { "API_KEY": "${input:apiKey}" }
 }
 }
}

Anti-Patterns

• Mega-tools: One tool that accepts a "command" string and switches behavior
• Untyped inputs: Using any or object for tool parameters
• Swallowed errors: Catching exceptions without returning isError: true
• Stateful servers: Storing session state in memory (use external stores)
• Missing descriptions: Tools without clear descriptions -> agents can't use them effectively
• Hardcoded secrets: API keys in server code -> use environment variables

Testing

// Use MCP Inspector for interactive testing
npx @modelcontextprotocol/inspector node dist/server.js

// Programmatic testing
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
const client = new Client({ name: "test", version: "1.0.0" });
// ... connect and call tools

Project Structure

my-mcp-server/
+-- src/
| +-- server.ts # Server setup + transport
| +-- tools/ # Tool implementations
| | +-- search.ts
| | -- create.ts
| +-- resources/ # Resource handlers
| | -- config.ts
| -- prompts/ # Prompt templates
| -- review.ts
+-- package.json
+-- tsconfig.json
-- .vscode/mcp.json # Local server config

Further Reading

• MCP Specification
• MCP TypeScript SDK
• MCP Python SDK
• VS Code MCP Integration