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A Sweet and Swifty YAML parser.
.package(url: "https://github.com/jpsim/Yams.git", from: "4.0.6")



A sweet and swifty YAML parser built on LibYAML.

SwiftPM xcodebuild pod lib lint Nightly codecov


Building Yams requires Xcode 11.x or a Swift 5.1+ toolchain with the Swift Package Manager or CMake and Ninja.


CMake 3.17.2 or newer is required, along with Ninja 1.9.0 or newer.

When building for non-Apple platforms:

cmake -B /path/to/build -G Ninja -S /path/to/yams -DCMAKE_BUILD_TYPE=Release -DFoundation_DIR=/path/to/foundation/build/cmake/modules
cmake --build /path/to/build

To build for Apple platforms (macOS, iOS, tvOS, watchOS), there is no need to spearately build Foundation because it is included as part of the SDK:

cmake -B /path/to/build -G Ninja -S /path/to/yams -DCMAKE_BUILD_TYPE=Release
cmake --build /path/to/build

Swift Package Manager

Add .package(url: "https://github.com/jpsim/Yams.git", from: "4.0.6") to your Package.swift file's dependencies.


Add pod 'Yams' to your Podfile.


Add github "jpsim/Yams" to your Cartfile.


In your WORKSPACE file

    name = "com_github_jpsim_yams",
    urls = [
        "https://github.com/jpsim/Yams/archive/%s.zip" % YAMS_GIT_SHA,
    strip_prefix = "yams-%s" % YAMS_GIT_SHA,


Yams has three groups of conversion APIs: one for use with Codable types, another for Swift Standard Library types, and a third one for a Yams-native representation.

Codable types

  • Codable is an encoding & decoding strategy introduced in Swift 4 enabling easy conversion between YAML and other Encoders like JSONEncoder and PropertyListEncoder.
  • Lowest computational overhead, equivalent to Yams.Node.
  • Encoding: YAMLEncoder.encode(_:) Produces a YAML String from an instance of type conforming to Encodable.
  • Decoding: YAMLDecoder.decode(_:from:) Decodes an instance of type conforming to Decodable from YAML String or Data.
import Foundation
import Yams

struct S: Codable {
    var p: String

let s = S(p: "test")
let encoder = YAMLEncoder()
let encodedYAML = try encoder.encode(s)
encodedYAML == """
p: test

let decoder = YAMLDecoder()
let decoded = try decoder.decode(S.self, from: encodedYAML)
s.p == decoded.p

Swift Standard Library types

  • The type of Swift Standard Library is inferred from the contents of the internal Yams.Node representation by matching regular expressions.
  • This method has the largest computational overhead When decoding YAML, because the type inference of all objects is done up-front.
  • It may be easier to use in such a way as to handle objects created from JSONSerialization or if the input is already standard library types (Any, Dictionary, Array, etc.).
  • Encoding: Yams.dump(object:) Produces a YAML String from an instance of Swift Standard Library types.
  • Decoding: Yams.load(yaml:) Produces an instance of Swift Standard Library types as Any from YAML String.
// [String: Any]
let dictionary: [String: Any] = ["key": "value"]
let mapYAML: String = try Yams.dump(object: dictionary)
mapYAML == """
key: value

let loadedDictionary = try Yams.load(yaml: mapYAML) as? [String: Any]

// [Any]
let array: [Int] = [1, 2, 3]
let sequenceYAML: String = try Yams.dump(object: array)
sequenceYAML == """
- 1
- 2
- 3

let loadedArray: [Int]? = try Yams.load(yaml: sequenceYAML) as? [Int]

// Any
let string = "string"
let scalarYAML: String = try Yams.dump(object: string)
scalarYAML == """

let loadedString: String? = try Yams.load(yaml: scalarYAML) as? String


  • Yams' native model representing Nodes of YAML which provides all functions such as detection and customization of the YAML format.
  • Depending on how it is used, computational overhead can be minimized.
  • Encoding: Yams.serialize(node:) Produces a YAML String from an instance of Node.
  • Decoding Yams.compose(yaml:) Produces an instance of Node from YAML String.
var map: Yams.Node = [
    "array": [
        1, 2, 3
map.mapping?.style = .flow
map["array"]?.sequence?.style = .flow
let yaml = try Yams.serialize(node: map)
yaml == """
{array: [1, 2, 3]}

let node = try Yams.compose(yaml: yaml)
map == node

Integrating with Combine

When Apple's Combine framework is available, YAMLDecoder conforms to the TopLevelDecoder protocol, which allows it to be used with the decode(type:decoder:) operator:

import Combine
import Foundation
import Yams

func fetchBook(from url: URL) -> AnyPublisher<Book, Error> {
    URLSession.shared.dataTaskPublisher(for: url)
        .decode(type: Book.self, decoder: YAMLDecoder())


Both Yams and libYAML are MIT licensed.


Stars: 741
Last commit: 5 weeks ago

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iOS Software Engineer @ Perry Street Software
Perry Street Software is Jack’d and SCRUFF. We are two of the world’s largest gay, bi, trans and queer social dating apps on iOS and Android. Our brands reach more than 20 million members worldwide so members can connect, meet and express themselves on a platform that prioritizes privacy and security. We invest heavily into SwiftUI and using Swift Packages to modularize the codebase.

Release Notes

15 weeks ago
  • None.
Bug Fixes
  • Fix build error when integrating Yams using CocoaPods.
    JP Simard

Swiftpack is being maintained by Petr Pavlik | @ptrpavlik | @swiftpackco | API