mcp4k

Overview

mcp4k is a comprehensive Kotlin framework that implements the vast majority of the MCP specification. It provides a compiler-driven approach that enforces correct parameter typing at compile time rather than runtime. The framework supports both client and server implementations with features for tools, resources, prompts, and sampling. It uses a clean API with annotations like @McpTool and @McpPrompt to define server capabilities. The framework currently supports stdio transport with other transports planned for future releases.

Try asking AI

After installing, here are 5 things you can ask your AI assistant:

• reverseStringinput: String

  Reverses an input string

  Try:Reverse the string 'hello'Try:Reverse 'mcp4k is great'
• sendEmailrecipients: List<String>, email: Email

  Sends an email with specified recipients and email content

  Try:Send email to 'test@example.com' with title 'Hello' and body 'World'Try:Send high priority email to team
• setUserNamename: String

  Sets the username in the server context

  Try:Set username to 'Alice'Try:Change username to 'Bob'
• greetUser

  Greets the user whose name is stored in the server context

  Try:Greet meTry:Say hello to the user
• toolThatAddsSecondTool

  A tool that adds another tool to the server at runtime

  Try:Add the second toolTry:Execute tool that adds another tool
• codeReviewPromptcode: String

  Generates a code review prompt based on the provided code

  Try:Review this code: 'fun hello() = println("hi")'Try:Help me review my Kotlin function
• slowToolOperationiterations: Int = 10

  Performs a slow operation with specified iterations

  Try:Run slow operation with 5 iterationsTry:Do a slow task with 20 iterations

Comparable tools

Installation

plugins {
  kotlin("multiplatform") version "2.3.21" // or kotlin("jvm")
  kotlin("plugin.serialization") version "2.3.21"

  id("sh.ondr.mcp4k") version "0.4.10" // <-- Add this
}

{
  "mcpServers": {
    "mcp4k-example": {
      "command": "java",
      "args": ["-jar", "path/to/your/mcp4k-server.jar"]
    }
  }
}

FAQ

What Kotlin versions are compatible with mcp4k?

Each mcp4k version is hard-linked to a specific Kotlin version. For example, version 0.4.10 requires Kotlin 2.3.21. Check the README for the full compatibility table.

Does mcp4k support transports other than stdio?

Currently, mcp4k only supports stdio transport, but HTTP-Streaming and other transports are planned for future releases.

Compare mcp4k with