JSON to Swift (Codable)

About this tool

Paste JSON from your API and get Swift types that conform to Codable, ready for JSONDecoder. Nested objects become their own type, arrays become [Type], and when a JSON key is not a good Swift name (snake_case or dashes) the converter writes CodingKeys so the original key is kept. Choose struct or final class, make every property optional, and use var instead of let if you need to change values.

How to use JSON in Swift

Swift reads JSON with Codable: decode Data into your type with JSONDecoder, and encode it back with JSONEncoder. With URLSession and async/await it takes a few lines.

struct User: Codable {
    let id: Int
    let name: String
    let email: String?
}

let url = URL(string: "https://api.example.com/users/1")!
let (data, _) = try await URLSession.shared.data(from: url)
let user = try JSONDecoder().decode(User.self, from: data)

Sending JSON to an API

To pass JSON data in a POST request, encode your value, put it in httpBody and set the Content-Type header to application/json.

var request = URLRequest(url: URL(string: "https://api.example.com/users")!)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = try JSONEncoder().encode(user)
let (data, response) = try await URLSession.shared.data(for: request)

Converting JSON to a string

JSONEncoder gives you Data. Turn it into a String with String(decoding: data, as: UTF8.self), and set encoder.outputFormatting = [.prettyPrinted, .sortedKeys] for readable output. In JavaScript the same job is JSON.stringify(value), and in Python json.dumps(value).

Swift, Kotlin, TypeScript and more

Building the same app for Android or the web? The JSON tools below make the matching Kotlin data class, TypeScript interface, C# class, Python dataclass and others from the same sample, so every client uses the same field names.