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🧱 A JSON decoding/encoding library that handles optimistically or strictly.
.package(url: "https://github.com/muukii/JAYSON.git", from: "2.4.0")

Do you need to handle the root cause of failure in decoding JSON?

We often process the value as a default value if it could not be decoded from JSON. (Recovering with a default value)
However, doing that might cause a serious problem and hide the actual root cause in the app.
Recovering with a default value is not a bad choice, it's important to know the JSON represents unexpected shape or value before recovering.

let json: JSON

do {
  self.id = try json.next("id").getString()
} catch {
  // We can know why decoding failed from error.
  // Not found "id" or "id" found but it was not `string` or something else.
  // that's why here recover the value to fill `self.id`
  self.id = "unknown"

JAYSON provides 2 ways of accessing to JSON object.

  1. Easy access (with dynamic-member-lookup)
let urlString: String? = json[3]?.shot?.images?.hidpi_image?.string
  1. Strict access (with dynamic-member-lookup)

We can know where error was caused. (with JSONError)

let id: String = try json


Build Status FOSSA Status Version License Platform Carthage compatible

Strict and Scalable JSON library. And also supports dynamicMemberLookup


Swift 5+ iOS📱, watchOS⌚️, tvOS📺, macOS🖥, Linux



Easy Access

let urlString: String? = json[3]?["shot"]?["images"]?["hidpi_image"]?.string

Using dynamicMemberLookup

let urlString: String? = json[3]?.shot?.images?.hidpi_image?.string

Strict Access (try-catch)

if the value does not exist, throw JSONError
Failed location can be known from JSONError

Get Value (String, Bool, Number)

let id: String = try json

Using dynamicMemberLookup

let id: String = try json

Get Value with Decoder (Custom Object)

Using the Decoder can be transformed in a custom object. And, throwable

let imageURL: URL = try json
    .get {
        URL.init(string: try $0.getString())!

General Getter

Strict getters

extension JSON {
    public func getDictionary() throws -> [String : JSON]
    public func getArray() throws -> [JSON]
    public func getNumber() throws -> NSNumber
    public func getInt() throws -> Int
    public func getInt8() throws -> Int8
    public func getInt16() throws -> Int16
    public func getInt32() throws -> Int32
    public func getInt64() throws -> Int64
    public func getUInt() throws -> UInt
    public func getUInt8() throws -> UInt8
    public func getUInt16() throws -> UInt16
    public func getUInt32() throws -> UInt32
    public func getUInt64() throws -> UInt64
    public func getString() throws -> String
    public func getBool() throws -> Bool
    public func getFloat() throws -> Float
    public func getDouble() throws -> Double

extension JSON {
    public func get<T>(_ s: (JSON) throws -> T) rethrows -> T

Optional Read-only properties😁

extension JSON {
    public var dictionary: [String : Any]? { get }
    public var array: [Any]? { get }
    public var string: String? { get }
    public var number: NSNumber? { get }
    public var double: Double? { get }
    public var float: Float? { get }
    public var int: Int? { get }
    public var uInt: UInt? { get }
    public var int8: Int8? { get }
    public var uInt8: UInt8? { get }
    public var int16: Int16? { get }
    public var uInt16: UInt16? { get }
    public var int32: Int32? { get }
    public var uInt32: UInt32? { get }
    public var int64: Int64? { get }
    public var uInt64: UInt64? { get }
    public var bool: Bool? { get }

Initialize JSON

let jsonData: Data = ...
let json = try JSON(data: jsonData)
let jsonData: Data
let json: Any = try JSONSerialization.jsonObject(with: data, options: [])
let json = try JSON(any: json)
let userInfo: [AnyHashable: Any]
let json = try JSON(any: json)
let objects: [Any]
let json = try JSON(any: json)

In the case of the following try it is not required.

let object: [String : JSON]
let json = JSON(object)
let object: [JSON]
let json = JSON(object)
let object: [JSONWritableType]
let json = JSON(object)
let object: [String : JSONWritableType]
let json = JSON(object)

Get current path (Debugging information.)

let path = try json

// path => "[0]["image"]["hidpi_image"]"


If you have access that does not exist key, throw JSONError.

public enum JSONError: Error {
  case notFoundKey(key: String, json: JSON)
  case notFoundIndex(index: Int, json: JSON)
  case failedToGetString(source: Any, json: JSON)
  case failedToGetBool(source: Any, json: JSON)
  case failedToGetNumber(source: Any, json: JSON)
  case failedToGetArray(source: Any, json: JSON)
  case failedToGetDictionary(source: Any, json: JSON)
  case decodeError(source: Any, json: JSON, decodeError: Error)
  case invalidJSONObject


do {
  let urlString: String = try json
    .next("foo") // ‼️ throw
} catch {

Output jsonError

Path: Root->["shots"][0]["user"]["profile_image"]
SourceType: dictionary

    large = "https://...";
    medium = "https://...";
    small = "https://...";

Go Back JSON hierarchy

try json
    .back() // <---

Import Example (dribbble API)

let json = try! JSON(data)

struct Shot {
    let id: Int
    let title: String
    let width: Int
    let height: Int
    let hidpiImageURLString: String?
    let normalImageURLString: String
    let teaserImageURLString: String

do {
    let shots: [Shot] = try json.getArray().map { json -> Shot in

        let imagesjson = try json.next("images")

        return Shot(
            id: try json.next("id").getInt(),
            title: try json.next("title").getString(),
            width: try json.next("width").getInt(),
            height: try json.next("height").getInt(),
            hidpiImageURLString: try? imagesjson.next("hidpi").getString(),
            normalImageURLString: try imagesjson.next("normal").getString(),
            teaserImageURLString: try imagesjson.next("teaser").getString()
} catch {

Write JSON

var json = JSON()
json["id"] = 18737649
json["active"] = true
json["name"] = "muukii"

var images = [String:JSON](https://raw.github.com/muukii/JAYSON/main/)
images["large"] = "http://...foo"
images["medium"] = "http://...bar"
images["small"] = "http://...fuzz"

json["images"] = JSON(images)

let data = try json.data(options: .prettyPrinted)

-> data

  "name" : "muukii",
  "active" : true,
  "id" : 18737649,
  "images" : {
    "large" : "http:\/\/...foo",
    "small" : "http:\/\/...fuzz",
    "medium" : "http:\/\/...bar"

json Convertible Examples

var json = JSON()

json["String"] = "String"
json["NSString"] = JSON("NSString" as NSString)
json["NSNumber"] = NSNumber(value: 0)
json["Int"] = 64
json["Int8"] = JSON(8 as Int8)
json["Int16"] = JSON(16 as Int16)
json["Int32"] = JSON(32 as Int32)
json["Int64"] = JSON(64 as Int64)

json["UInt"] = JSON(64 as UInt)
json["UInt8"] = JSON(8 as UInt8)
json["UInt16"] = JSON(16 as UInt16)
json["UInt32"] = JSON(32 as UInt32)
json["UInt64"] = JSON(64 as UInt64)

json["Bool_true"] = true
json["Bool_false"] = false

json["Float"] = JSON(1.0 / 3.0 as Float)
json["Double"] = JSON(1.0 / 3.0 as Double)
json["CGFloat"] = JSON(1.0 / 3.0 as CGFloat)


json is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "JAYSON"


muukii, muukii.app@gmail.com


json is available under the MIT license. See the LICENSE file for more info.

FOSSA Status


Stars: 246
Last commit: 2 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

2 weeks ago

Number of PRs : 2

tag number of PRs
Breaking change 2

Group: Enhancement (2)

  • Introduce JSON.contains #22 by @muukii
    • Breaking change
  • Delete dynamic member lookup #21 by @muukii
    • Breaking change

Other (0)

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