MCPServerKit

A reusable Swift package for embedding MCP (Model Context Protocol) servers in macOS/iOS apps.

Features

• JSON-RPC 2.0 HTTP server with connection management
• Tool registry for registering and dispatching tool definitions
• Configuration abstraction for flexible settings storage
• Tool handler protocol with convenience helpers
• LAN mode support for network access control

Installation

Add MCPServerKit as a Swift Package dependency:

dependencies: [
  .package(url: "https://github.com/crunchybananas/MCPServerKit.git", from: "1.0.0")
]

Then add MCPServerKit to your target's dependencies:

.target(name: "YourApp", dependencies: ["MCPServerKit"])

MCPServerKit automatically brings in MCPCore as a transitive dependency.

Quick Start

import MCPServerKit

// Create server with registry
let registry = MCPToolRegistry()
let server = MCPServer(port: 8765, registry: registry)

// Register tool definitions
registry.register(MCPToolDefinition(
  name: "my.tool",
  description: "Does something useful",
  inputSchema: ["type": "object", "properties": [:]],
  category: .state,
  isMutating: false
))

// Register tool handler
registry.register(handler: MyToolHandler())

// Start server
server.start()

Architecture

MCPServer

The main server class handles:

• TCP listener on configurable port
• HTTP request parsing
• JSON-RPC 2.0 protocol
• Connection lifecycle
• LAN mode enforcement

MCPToolRegistry

Manages tool definitions and handlers:

• Register/lookup tool definitions
• Register tool handlers
• Permission checking
• tools/list response building

MCPToolHandling

Protocol for implementing tool handlers:

@MainActor
public protocol MCPToolHandling: AnyObject {
  var supportedTools: Set<String> { get }
  func handle(name: String, id: Any?, arguments: [String: Any]) async -> (Int, Data)
}

MCPServerConfigProviding

Protocol for configuration storage:

@MainActor
public protocol MCPServerConfigProviding {
  func bool(forKey: String, default: Bool) -> Bool
  func integer(forKey: String, default: Int) -> Int
  func string(forKey: String, default: String) -> String
  // ... setters
}

Default implementation MCPUserDefaultsConfig uses UserDefaults.

Custom Request Handling

For app-specific methods, use the onRequest callback:

server.onRequest = { method, id, params in
  switch method {
  case "myapp.customMethod":
    return (200, JSONRPCResponseBuilder.makeResult(id: id, result: ["ok": true]))
  default:
    return nil // Fall through to built-in handling
  }
}

Platform Requirements

• macOS 15.0+
• iOS 18.0+
• Swift 6.0+

Dependencies

• MCPCore (types and JSON-RPC utilities)