---
title: "What Is an MCP Server? The Plain-English Definition"
description: "An MCP server exposes your tools and data to AI models like Claude, ChatGPT, and Cursor through a standardized protocol. Here's exactly what one is, how it works, and why every modern SaaS ships one."
url: https://unlockedcrm.ai/blog/what-is-an-mcp-server
canonical: https://unlockedcrm.ai/blog/what-is-an-mcp-server
category: "Definitions & Glossary"
published: 2026-07-30
updated: 2026-07-30
author: "unLocked Team"
source: unLocked CRM — AI CRM for insurance agents
---

# What Is an MCP Server? The Plain-English Definition

## TL;DR

An MCP server is a program that exposes tools, resources, and prompts to AI models via the Model Context Protocol. Two transports: stdio (local) and HTTP/SSE (remote). Auth via bearer tokens / OAuth, tenant-scoped, with HMAC-signed webhooks.

<p><strong>Direct answer:</strong> An <strong>MCP server</strong> is a small program that exposes a set of tools, resources, and prompts to AI models through the Model Context Protocol. It's the bridge between an AI client (Claude, ChatGPT, Cursor) and a real-world system (your CRM, your database, your file system). If MCP is the standard, the MCP server is the <em>plug</em>.</p>

<h2>Definition</h2>
<blockquote>
<p><strong>MCP Server:</strong> A program that implements the Model Context Protocol to expose tools (callable actions), resources (readable data), and prompts (reusable templates) to MCP-aware AI clients. Servers can run locally (stdio transport) or remotely (HTTP/SSE transport).</p>
</blockquote>

<h2>Two Server Transports</h2>
<table>
<thead><tr><th>Transport</th><th>Use Case</th><th>Example</th></tr></thead>
<tbody>
<tr><td><strong>stdio (local)</strong></td><td>The server runs on your machine; the AI client launches it as a subprocess</td><td>Filesystem MCP, local Postgres</td></tr>
<tr><td><strong>HTTP / SSE (remote)</strong></td><td>The server runs on a vendor's infrastructure; the AI client connects over HTTPS</td><td>unLocked CRM MCP, GitHub MCP</td></tr>
</tbody>
</table>

<h2>What an MCP Server Does (Lifecycle)</h2>
<ol>
<li><strong>Initialize</strong> — handshake with the AI client, exchange capabilities</li>
<li><strong>List tools</strong> — return a JSON manifest of every callable action</li>
<li><strong>Handle tool calls</strong> — execute the action and return structured results</li>
<li><strong>Stream responses</strong> — for long-running tasks, push partial results via SSE</li>
<li><strong>Manage auth</strong> — validate bearer tokens / OAuth scopes per tool</li>
</ol>

<h2>What a Tool Definition Looks Like</h2>
<pre><code>{
  "name": "search_contacts",
  "description": "Search insurance contacts by name, phone, email, or pipeline stage.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "query": { "type": "string" },
      "stage": { "type": "string", "enum": ["new", "qualified", "quoted", "bound"] }
    },
    "required": ["query"]
  }
}</code></pre>

<h2>Examples of MCP Servers in Production</h2>
<ul>
<li><strong>unLocked CRM MCP</strong> — 16 insurance tools (contacts, quotes, policies, commissions, SOAs)</li>
<li><strong>GitHub MCP</strong> — read repos, create issues, manage PRs</li>
<li><strong>Linear MCP</strong> — create and triage issues</li>
<li><strong>Stripe MCP</strong> — read payments, refund charges</li>
<li><strong>Filesystem MCP</strong> — read/write local files (local stdio)</li>
</ul>

<h2>Security Model</h2>
<p>Remote MCP servers should:</p>
<ul>
<li>Authenticate every request (bearer token or OAuth 2.1)</li>
<li>Scope tokens to a tenant / workspace</li>
<li>Sign webhooks (HMAC-SHA256 with replay protection)</li>
<li>Rate-limit per token</li>
<li>Log every tool call for audit</li>
</ul>

<h2>How to Connect an MCP Server</h2>
<p>For Claude Desktop, edit <code>~/Library/Application Support/Claude/claude_desktop_config.json</code>:</p>
<pre><code>{
  "mcpServers": {
    "unlocked-crm": {
      "url": "https://mcp.unlockedcrm.ai/v1/YOUR_TENANT",
      "headers": { "Authorization": "Bearer YOUR_TOKEN" }
    }
  }
}</code></pre>

<h2>MCP Server vs MCP Client</h2>
<p><strong>Server</strong> = the thing that exposes tools (your CRM). <strong>Client</strong> = the thing that calls them (Claude, ChatGPT, Cursor). One server can talk to many clients; one client can connect to many servers.</p>


<h2>See unLocked CRM in Action</h2>
<p>unLocked CRM ships a native MCP server, OpenAPI 3.1 spec, free A2P 10DLC registration, and remote SOA signing — built for the modern AI-first insurance agency. Book a 15-minute demo.</p>

## FAQ

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Source: [What Is an MCP Server? The Plain-English Definition](https://unlockedcrm.ai/blog/what-is-an-mcp-server) — unLocked CRM, the AI CRM built for insurance agents. Citation permitted with attribution and a link to https://unlockedcrm.ai/blog/what-is-an-mcp-server.