MCP Kotlin Minimal Client Server Sample

🚀 MCP (Model Context Protocol) Minimal Kotlin Client-Server Example

A simple weather tool demonstrating the interaction between a client and a server using the Model Context Protocol (MCP). For demonstration purposes only.

User: "What's the weather like in Tokyo?"
Response: "The weather in Tokyo is sunny."

This is a Kotlin version of mcp-minimal-client-weather-server-sample.

Client: src/main/kotlin/Client.kt
Server: server.main.kts

🚀 Quick Start

This project is a simple weather tool that showcases the interaction between a client and a server using the Model Context Protocol (MCP). It's designed for demonstration purposes.

✨ Features

• Demonstrates client-server interaction using MCP.
• Provides a simple weather query and response mechanism.

📚 Documentation

Initialization and Tool Discovery

Figure 1: Initialization and Tool Discovery

sequenceDiagram
    autonumber

    participant User
    participant ClientApp as ClientApp (Host)<br>on local PC
    participant LLM as LLM (e.g., Claude)<br>remote service
    participant MCPClient as MCPClient (internal component)<br>on local PC of client app
    participant MCPServer as MCPServer (e.g., tool server)<br>on local PC

    Note over User, MCPServer: User starts the client application and initiates a connection to MCPServer

    ClientApp->>+MCPClient: Instruction to connect to the server
    MCPClient->>-MCPServer: Connection established (WebSocket or HTTP long polling)

    Note over MCPClient, MCPServer: Communication channel between client and server is established

    ClientApp->>+MCPClient: Instruction to get the list of available tools (session.list_tools())
    MCPClient->>+MCPServer: Tool list request (tools/list)
    MCPServer-->-MCPClient: Return the list of available tools
    MCPClient-->>-ClientApp: Notify that the tool list has been obtained

    Note over ClientApp: Display the tool list or output tool information in the console

Tool Execution Flow

Figure 2: Tool Execution Flow

sequenceDiagram
    autonumber

    participant User
    participant ClientApp as ClientApp (Host)<br>on local PC
    participant LLM as LLM (e.g., Claude)<br>remote service
    participant MCPClient as MCPClient (internal component)<br>on local PC of client app
    participant MCPServer as MCPServer (e.g., tool server)<br>on local PC

    Note over User: User inputs the query "What's the weather like in Tokyo?"

    ClientApp->>LLM: Send the user query to get a preliminary response
    LLM-->>ClientApp: Return an instruction to call a tool

    ClientApp->>+MCPClient: Instruction to execute the tool call (session.call_tool())
    MCPClient->>+MCPServer: Tool call request (tools/call)

    Note over MCPServer: Execute the get_weather function and return the result
    MCPServer-->>-MCPClient: Return the weather information

    MCPClient-->>-ClientApp: Notify the result of the tool execution

    ClientApp->>LLM: Send the tool execution result to get the final response
    LLM-->>ClientApp: Return the final answer

    ClientApp->>User: Display the final response