json to swift codable struct converter
typetools
instant, client-side type converter • 0ms network latency
import Foundation
struct Metadata: Codable, Equatable {
let lastLogin: String
let ipAddress: String
let failedAttempts: String?
}
struct RootPayload: Codable, Equatable {
let userId: String
let username: String
let email: String
let isActive: Bool
let score: Double
let roles: [String]
let metadata: Metadata
let tags: [AnyCodable]
}step-by-step integration guide
technical specification differences & end-to-end conversion workflow
Value-Type Semantics and Swift Codable Synthesis vs. Dynamic JSON
In modern iOS and macOS engineering, Swift relies on stack-allocated value types (struct) conforming to the Codable (Decodable & Encodable) and Sendable protocols rather than legacy Objective-C NSDictionary dynamic casting. Swift's compiler automatically synthesizes the init(from decoder: Decoder) implementation at compile time, provided every stored property in the struct also conforms to Codable. However, if a single non-optional property in a Swift struct is missing or null in the incoming JSON payload, JSONDecoder immediately throws a DecodingError.keyNotFound or DecodingError.valueNotFound, aborting the entire response parse.
Generating CodingKeys Enums, Sendable Value Types, and Optional Properties
Our client-side JSON-to-Swift converter analyzes your JSON syntax tree and emits clean Swift structs using immutable let bindings. Whenever JSON keys use snake_case, kebab-case, or reserved Swift keywords (such as protocol, extension, class, or default), the generator normalizes the Swift property name to idiomatic camelCase and synthesizes a nested enum CodingKeys: String, CodingKey mapping each Swift identifier to its exact JSON wire key. Furthermore, the AST analyzer inspects array elements for sparse or nullable keys and marks them as Swift Optionals (String?, Int?, Double?) so JSONDecoder gracefully decodes null and omitted keys as nil.
frequently asked questions
common developer questions answered
q:When do I need a CodingKeys enum vs. using keyDecodingStrategy = .convertFromSnakeCase?
Explicit CodingKeys enums are safer and faster because they work regardless of how a caller configures JSONDecoder, and they also handle irregular keys, acronyms (like userURL or htmlBody), and reserved Swift keywords.
q:Why are the generated models Swift structs instead of classes?
Swift structs are value types allocated on the stack (without ARC reference-counting overhead) and automatically satisfy Swift 6 strict concurrency Sendable requirements when all stored properties are Sendable.
q:How does the converter handle empty JSON arrays [] in Swift?
Because Swift requires an explicit generic element type for every Array, empty JSON arrays are typed safely as [AnyCodable] or [String] placeholder slices so the struct compiles cleanly.