FastMCP

The fastest way to build MCP servers in Swift.

try await FastMCP.builder()
    .name("My Server")
    .addTools([WeatherTool()])
    .run()

Three lines to a working MCP server over stdio. Or serve over HTTP:

try await FastMCP.builder()
    .name("My Server")
    .addTools([WeatherTool()])
    .transport(.http(port: 8080))
    .run()

Installation

Add to your Package.swift:

dependencies: [
    .package(url: "https://github.com/mehmetbaykar/swift-fast-mcp", from: "2.1.0")
]

Then add "FastMCP" as a dependency of your target:

.target(
    name: "MyServer",
    dependencies: [
        .product(name: "FastMCP", package: "swift-fast-mcp")
    ]
)

FastMCP pulls in these dependencies automatically:

• swift-sdk -- Official MCP Swift SDK
• swift-mcp-toolkit -- Tool/Resource/Prompt protocol abstractions
• swift-service-lifecycle -- Graceful shutdown
• swift-log -- Logging
• swift-nio -- HTTP transport (NIO is an internal dependency; not re-exported)

Quick Start

Stdio transport (default)

import FastMCP

struct WeatherTool: MCPTool {
    let name = "get_weather"
    let description: String? = "Get weather for a location"

    @Schemable
    struct Parameters: Sendable {
        let location: String
    }

    func call(with args: Parameters) async throws(ToolError) -> Content {
        [ToolContentItem(text: "Weather in \(args.location): 22C, Sunny")]
    }
}

@main
struct MyServer {
    static func main() async throws {
        try await FastMCP.builder()
            .name("Weather Server")
            .addTools([WeatherTool()])
            .run()
    }
}

Connect it to Claude Desktop by adding to claude_desktop_config.json:

{
    "mcpServers": {
        "weather": {
            "command": "/path/to/my-server"
        }
    }
}

HTTP transport

@main
struct MyServer {
    static func main() async throws {
        try await FastMCP.builder()
            .name("Weather Server")
            .addTools([WeatherTool()])
            .transport(.http(port: 8080))
            .run()
        // Listening on http://127.0.0.1:8080/mcp
    }
}

Transport Options

public enum Transport: Sendable {
    case stdio
    case inMemory
    case http(
        mode: HTTPMode = .stateful,
        host: String = "127.0.0.1",
        port: Int = 3000,
        endpoint: String = "/mcp"
    )
    case custom(MCP.Transport)
}

| Transport | Use Case | |-----------|----------| | .stdio | Claude Desktop, CLI tools. Default. | | .inMemory | Unit testing. | | .http(...) | Remote servers, multi-client access, web deployments. | | .custom(transport) | Provide your own MCP.Transport implementation. |

HTTPMode

public enum HTTPMode: Sendable {
    case stateful
    case stateless
}

Stateful (default) -- Full MCP Streamable HTTP. Each client gets a session with SSE streaming, resumability via Last-Event-ID, GET for server-initiated messages, and DELETE for session teardown.

Stateless -- Minimal HTTP. No sessions, direct JSON responses, POST only. Use when session management is handled externally or not needed.

// Stateful (default)
.transport(.http(port: 8080))
.transport(.http(mode: .stateful, host: "0.0.0.0", port: 3000, endpoint: "/mcp"))

// Stateless
.transport(.http(mode: .stateless, port: 8080))

Builder API

All builder methods return a new Builder (value semantics) and can be chained.

Server metadata

.name("My Server")               // Server name (default: process name)
.version("2.1.0")                // Server version (default: "1.0.0")
.title("My Display Name")        // Human-readable display name for UIs


... [View full README on GitHub](https://github.com/mehmetbaykar/swift-fast-mcp#readme)