Working with YAML in Swift: Yams Library for iOS/macOS

Working with YAML in Swift (iOS/macOS): Yams Library

YAML (YAML Ain't Markup Language) is a convenient data serialization format often used for configuration files, dependency descriptions (e.g., docker-compose.yml), and projects requiring a readable and concise data structure. In the Apple ecosystem, several libraries exist for working with YAML in Swift, but the most popular and stable is Yams — a fast and easy-to-use library written in pure Swift.

What is Yams?

Yams is an open-source library that provides full support for parsing and serializing YAML in Swift. It is compatible with iOS, macOS, tvOS, and watchOS. Yams supports the YAML 1.2 specification and allows converting YAML strings into Swift structures (dictionaries, arrays, strings, numbers, booleans) and back.

Key features of Yams:

• Parsing a YAML string into Any (typically [String: Any] or [Any]).
• Serializing Swift objects back to YAML.
• Support for nested structures, arrays, and multiple documents.
• Error handling with detailed messages.
• Fully compatible with Swift Package Manager (SPM) and CocoaPods.

Installing Yams in Your Project

You can install Yams via Swift Package Manager (recommended) or CocoaPods.

Via Swift Package Manager

1. In Xcode, select File → Add Packages.
2. Paste the repository URL: https://github.com/jpsim/Yams.git
3. Choose a version (latest stable is recommended) and click Add Package.

Or add the dependency in Package.swift:

// swift-tools-version:5.7import PackageDescription

let package = Package(    name: "MyProject",    dependencies: [        .package(url: "https://github.com/jpsim/Yams.git", from: "5.0.0")    ],    targets: [        .target(            name: "MyProject",            dependencies: ["Yams"])    ])

Via CocoaPods

Add the line to your Podfile:

pod 'Yams', '~> 5.0'

Then run pod install.

Basic Usage: Parsing YAML

After installation, import the library and use Yams.load(yaml:) to parse a string.

import Yams

let yamlString = """name: Swifttype: languageversions:  - 5.5  - 5.6  - 5.7features:  protocol_oriented: true  value_semantics: true"""

do {    if let data = try Yams.load(yaml: yamlString) as? [String: Any] {        print("Name: \\(data["name"] ?? "")")        print("Versions: \\(data["versions"] ?? [])")        if let features = data["features"] as? [String: Bool] {            print("Protocol oriented: \\(features["protocol_oriented"] ?? false)")        }    }} catch {    print("YAML parsing error: \\(error.localizedDescription)")}

Output:

Name: SwiftVersions: [5.5, 5.6, 5.7]Protocol oriented: true

Serializing Swift Objects to YAML

For reverse conversion, use Yams.dump(object:):

import Yams

let dictionary: [String: Any] = [    "app": "MyApp",    "version": 2.0,    "features": ["dark_mode", "notifications"],    "settings": [        "autosave": true,        "timeout": 30    ]]

do {    let yamlString = try Yams.dump(object: dictionary)    print(yamlString)} catch {    print("Serialization error: \\(error.localizedDescription)")}

Output:

app: MyAppfeatures:  - dark_mode  - notificationssettings:  autosave: true  timeout: 30