mcp-server-patterns

MCP Server Patterns

The Model Context Protocol (MCP) lets AI assistants call tools, read resources, and use prompts from your server. Use this skill when building or maintaining MCP servers, or integrating with the official Salesforce MCP server. The SDK API evolves; check Context7 (query-docs for "MCP") or the official MCP documentation for current method names and signatures.

When to Use

Use when: implementing a new MCP server, adding tools or resources, choosing stdio vs HTTP, integrating with @salesforce/mcp, upgrading the SDK, or debugging MCP registration and transport issues.

How It Works

Core Concepts

• Tools: Actions the model can invoke (e.g. search, run a command). Register with registerTool() or tool() depending on SDK version.
• Resources: Read-only data the model can fetch (e.g. file contents, API responses). Register with registerResource() or resource(). Handlers typically receive a uri argument.
• Prompts: Reusable, parameterised prompt templates the client can surface (e.g. in Claude Desktop). Register with registerPrompt() or equivalent.
• Transport: stdio for local clients (e.g. Claude Desktop); Streamable HTTP is preferred for remote (Cursor, cloud). Legacy HTTP/SSE is for backward compatibility.

The Node/TypeScript SDK may expose tool() / resource() or registerTool() / registerResource(); the official SDK has changed over time. Always verify against the current MCP docs or Context7.

Transport Decision Guide

Transport	Use When	Examples
stdio	Local client, same machine, Claude Desktop/Code	Development, local testing
Streamable HTTP	Remote clients, cloud deployment, multi-user	Cursor, production APIs
Legacy HTTP/SSE	Backward compatibility only	Older clients

Keep server logic (tools + resources) independent of transport so you can plug in stdio or HTTP in the entrypoint.

Examples

Install and Server Setup

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" });

// Register a tool
server.tool(
  "search-records",
  "Search Salesforce records by keyword",
  { query: z.string(), objectType: z.string().default("Account") },
  async ({ query, objectType }) => {
    // Your implementation here
    return { content: [{ type: "text", text: JSON.stringify(results) }] };
  }
);

// Connect via stdio
const transport = new StdioServerTransport();
await server.connect(transport);

Note: Registration API varies by SDK version — some versions use positional args server.tool(name, description, schema, handler), others use object syntax. Check the official MCP docs or Context7 for current @modelcontextprotocol/sdk signatures.

Use Zod (or the SDK's preferred schema format) for input validation.

Salesforce MCP Integration

Official @salesforce/mcp Server

MCP config is auto-installed by npx scc-universal install (.mcp.json for Claude Code, .cursor/mcp.json for Cursor). The official @salesforce/mcp server provides these toolsets:

Toolset	What It Does
orgs	Org management, auth, user info
metadata	Deploy, retrieve, list metadata types
data	SOQL queries, record CRUD, bulk operations
users	User management, permission sets
testing	Run Apex tests, get coverage results
code-analysis	PMD/scanner, code quality checks
lwc-experts	LWC development guidance
devops	Source tracking, scratch org operations

Using @salesforce/mcp in Claude Code

{
  "mcpServers": {
    "salesforce": {
      "command": "npx",
      "args": ["-y", "@salesforce/mcp@latest"],
      "env": {
        "SF_ORG_ALIAS": "my-org"
      }
    }
  }
}

Building Custom Salesforce MCP Tools

When @salesforce/mcp doesn't cover your use case (org-specific business logic, custom validation rules, internal APIs), build a custom MCP server:

import { execFileSync } from "child_process";

server.tool(
  "validate-account-hierarchy",
  "Check account hierarchy depth and circular references",
  { accountId: z.string().regex(/^[a-zA-Z0-9]{15,18}$/, "Must be a valid 15- or 18-char Salesforce ID") },
  async ({ accountId }) => {
    const result = execFileSync("sf", [
      "data", "query",
      "--sobject", "Account",
      "--where", `Id='${accountId}'`,
      "--fields", "Id,ParentId",
      "--json"
    ], { timeout: 30000, encoding: "utf-8" });
    return { content: [{ type: "text", text: result }] };
  }
);

Best Practices

• Schema first: Define input schemas with Zod for every tool; document parameters and return shape.
• Input validation: Validate and sanitize all inputs before passing to SF CLI or SOQL. Never interpolate raw user input into shell commands or queries.
• Errors: Return structured errors or messages the model can interpret; avoid raw stack traces.
• Idempotency: Prefer idempotent tools where possible so retries are safe.
• Timeouts: Set explicit timeouts on execSync/exec calls (e.g., { timeout: 30000 }) and on HTTP requests.
• Security: Never pass raw user input to SOQL queries — use bind variables or parameterized queries. Use Named Credentials for external callouts. Validate Salesforce IDs with Zod regex (/^[a-zA-Z0-9]{15,18}$/) before passing to SF CLI.

Official SDKs and Docs

• JavaScript/TypeScript: @modelcontextprotocol/sdk (npm). Use Context7 with library name "MCP" for current registration and transport patterns.
• Go: Official Go SDK on GitHub (modelcontextprotocol/go-sdk).
• C#: Official C# SDK for .NET.
• Salesforce MCP: @salesforce/mcp (npm) — official Salesforce MCP server.