Swift MCP Server

Project Goal

Reimplement the 3 core MCP servers (filesystem, git, fetch) as a single Swift binary called mcpx.

Why Swift?

• Single binary deployment (no Node.js dependency)
• Native macOS performance
• Clean, modern syntax
• Excellent Foundation library for filesystem/networking
• First-class MCP Swift SDK available

Architecture Overview

Single Binary, Multiple Tools

mcpx
├── fs    (filesystem operations)
├── git   (git operations) 
└── fetch (HTTP requests)

Command Structure

mcpx --allow-dir /path/to/project
# Exposes all three tool sets via MCP protocol

Core Requirements

1. Filesystem Server (fs)

Tools to implement:

• read_file - Read file contents with UTF-8 encoding
• write_file - Create/overwrite files
• list_directory - List directory contents with [FILE]/[DIR] prefixes
• create_directory - Create directories recursively
• move_file - Move/rename files and directories
• search_files - Recursive file search with pattern matching
• get_file_info - File metadata (size, dates, permissions)

Key APIs:

• FileManager.default for directory operations
• String(contentsOf:) and Data.write(to:) for file I/O
• FileManager.contentsOfDirectory(atPath:) for listings

2. Git Server (git)

Tools to implement:

• git_status - Show working directory status
• git_add - Stage files
• git_commit - Create commits
• git_push - Push to remote
• git_pull - Pull from remote
• git_log - Show commit history
• git_diff - Show file differences
• git_branch - Branch operations

Implementation approach:

• Use Process to execute git commands
• Parse stdout/stderr for structured responses
• Handle git credential management

3. Fetch Server (fetch)

Tools to implement:

• http_get - GET requests with headers
• http_post - POST requests with body/headers
• http_put - PUT requests
• http_delete - DELETE requests

Key APIs:

• URLSession for HTTP requests
• JSONSerialization for JSON handling
• Proper error handling for network failures

Project Structure

Sources/
├── SwiftMCP/
│   ├── main.swift           # Entry point
│   ├── MCPServer.swift      # MCP protocol handling
│   ├── FilesystemTools.swift
│   ├── GitTools.swift
│   └── FetchTools.swift
└── Package.swift

Dependencies

// Package.swift
dependencies: [
    .package(url: "https://github.com/modelcontextprotocol/swift-sdk", from: "1.0.0")
]

Security Requirements

• Path validation - Only allow operations within specified directories
• Git safety - Validate git commands to prevent injection
• HTTP limits - Reasonable timeouts and request size limits
• Error handling - Never expose internal system paths in errors

MCP Protocol Integration

• Use the official Swift MCP SDK
• Implement ListToolsRequestSchema handler
• Implement CallToolRequestSchema handler
• Follow MCP tool schema patterns from Node.js versions

Success Criteria

1. Drop-in replacement - Same MCP tool interface as Node.js versions
2. Single binary - No runtime dependencies
3. Better performance - Faster than Node.js equivalents
4. Clean error messages - User-friendly error handling
5. Cross-platform - Works on macOS and Linux

Implementation Order

1. Start with filesystem - Core functionality, easiest to test
2. Add fetch - HTTP operations, good for testing network handling
3. Finish with git - Most complex due to subprocess management

Testing Strategy

• Test against existing MCP clients (Claude Desktop)
• Compare output format with Node.js versions
• Test edge cases: large files, network failures, git errors
• Verify security boundaries work correctly

Key Differences from Node.js Version

• No async/await ceremony - Use Swift's structured concurrency
• Native error types - Proper Swift error handling vs JavaScript exceptions
• Type safety - Compile-time guarantees vs runtime schema validation
• Resource management - Automatic memory management vs manual cleanup