🧱 A JSON decoding/encoding library that handles optimistically or strictly.





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Last Commit

3mos ago










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]()
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.

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