YamlToJSON.swift

import SwiftUI
import Yams

extension String {
    var yamlToJSON: String {
        do {
            guard let parsed = try Yams.load(yaml: self) else { return "" }
            let data = try JSONSerialization.data(withJSONObject: parsed, options: [.sortedKeys, .prettyPrinted])
            return String(decoding: data, as: UTF8.self)
        } catch {
            return "\(error)"
        }
    }
}

@main
struct YamlToJSONApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

struct ContentView: View {
    @State var input = ""
    var body: some View {
        HSplitView {
            TextEditor(text: $input)
            TextEditor(text: .constant(input.yamlToJSON))
        }
    }
}

https://gist.github.com/helje5 commented:

As a swift-sh script:

#!/usr/bin/swift sh

import Foundation
import Yams // @jpsim

guard CommandLine.arguments.count > 1 else {
  print("usage: tool file.yaml [file.json]")
  exit(42)
}

do {
  let input  = try String(contentsOfFile: CommandLine.arguments[1])
  let parsed = try Yams.load(yaml: input) ?? [:]
  let data   = try JSONSerialization
	   .data(withJSONObject: parsed, options: [.sortedKeys, .prettyPrinted])

  if CommandLine.arguments.count > 2 {
	  try data.write(to: URL(fileURLWithPath: CommandLine.arguments[2]))
  }
  else if let output = String(data: data, encoding: .utf8) {
	  print(output)
  }
  else if !data.isEmpty {
	  print("Could not convert data?!")
	  exit(44)
  }
}
catch {
  print("Errors happen:", error)
  exit(43)
}