MCP Server

In MCP (Model Context Protocol), the MCP server is a core concept.
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What Is an MCP Server?

An MCP server provides a standardized interface that connects an AI model so it can access external resources such as tools, data, and APIs.
Simply put, it is a server that provides a collection of tools AI can use.

Structure

MCP is broadly divided into clients and servers:

  • MCP client
    • An application attached to an LLM environment, such as an IDE, chat UI, or notebook
    • Receives the user’s prompt, runs the model, and sends requests to the MCP server when needed
  • MCP server
    • Manages and provides multiple resources/tools/functions
    • Communicates with clients through a standardized protocol based on JSON-RPC
    • Examples: DB query server, file system server, API call server

MCP Client Server

What the Server Provides

An MCP server mainly provides four functions:

  1. Resources
    • Databases, files, documents, API responses, and more
    • Examples: resource://db/customers, resource://filesystem/project/README.md
  2. Tools
    • Callable functions or actions
    • Examples: searchCustomer(name), sendEmail(to, subject, body)
  3. Prompts
    • Provides predefined templates
    • Example: “Prompt for generating SQL queries”
  4. Events
    • Delivers notifications or change events from the server in real time

Example Flow

  1. A user enters in an IDE: “Search for customer ‘Hong Gil-dong’ in the DB”
  2. The LLM decides it should call the “searchCustomer” tool through the MCP client
  3. MCP client -> MCP server sends the request
  4. The MCP server performs the actual DB lookup and returns the result
  5. The LLM summarizes the result in user-friendly language and displays it

MCP Server Example

For example, a file system MCP server might provide:

  • Resource: Files in a project folder, such as /src/main.kt and /README.md
  • Tools: File reading, writing, and search functions such as readFile and writeFile
  • Prompts: Templates such as “Refactor this code”

When a server configured this way is connected, AI can directly explore and modify project files.

Analogy

  • MCP server = “hotel concierge”
    • When a guest (LLM) asks, “Recommend tourist attractions,” the concierge handles multiple APIs and databases behind the scenes and provides organized information
  • MCP client = “hotel front desk”
    • Talks directly with the guest, receives requests, and forwards them to the concierge

Summary

An MCP server acts as a backend that provides a standardized interface so an LLM can use external tools and data safely and consistently.