MCP Kotlin Minimal Client Server Sample

A simple Kotlin weather query client-server example based on the MCP protocol, demonstrating the tool invocation process.

Developer tools Artificial intelligence chatbots #Tool Invocation #Protocol Interaction #Weather Query .kotlin

rating : 2.5 points

downloads : 18

update time : 2025-04-28

What is an MCP server?

An MCP server is an intermediate layer protocol used to connect large language models (LLMs) with specific tools. It allows LLMs to call external tools through a standardized interface, enabling broader functional expansion.

How to use an MCP server?

Users can communicate with the MCP server through a client application, request the functions of specific tools, and receive the returned results.

Applicable scenarios

Suitable for scenarios that require calling external tools to complete complex tasks, such as weather queries and database operations.

Main Features

Tool Registration and DiscoverySupports dynamic registration and listing of available tools on the server.

Standard JSON-RPC InterfaceProvides a standard communication protocol based on JSON-RPC to ensure efficient and stable data exchange.

Permission ControlSupports permission verification for tool invocation to ensure data security.

Advantages and Limitations

Advantages

Unifies the tool access method, reducing development costs.

Supports concurrent invocation of multiple tools, improving work efficiency.

Easy to integrate into existing systems.

Limitations

Requires a stable network connection.

Some advanced features may require additional configuration.

How to Use

Install the MCP Client

Download and install the MCP client software, ensuring its version is compatible with the target server.

Start the MCP Server

Run the MCP server to listen for client requests.

Configure Tools

Usage Examples

Query the Weather in TokyoA user asks about the weather in Tokyo, and the MCP server calls the corresponding tool and returns the result.

Perform a Mathematical OperationA user requests to calculate the sum of two numbers, and the MCP server calls the mathematical tool and returns the result.

Frequently Asked Questions

Does the MCP server support custom tools?

How to ensure the security of data transmission?

Related Resources

Official Documentation

Detailed API documentation and usage guides.

GitHub Repository

An open-source code repository. Contributions and improvements are welcome.

Demo Video

Quickly understand the working principle of the MCP server.

🚀 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