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JSON to Swift Converter (Free AI Tool)
Convert JSON to Swift Codable structs instantly for iOS and macOS development. Generate type-safe Swift models from REST API responses with automatic optional detection and nested struct creation. Eliminate manual model writing and ensure compile-time type safety.
Paste code in both editors to see differences
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Hint: Paste your code, customize font size and line numbers, then click Export PDF to download formatted code.
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Hint: Select conversion type, paste your data, and get instant conversion. Supports JSON, YAML, XML, Excel, PDF, and more.
How It Works
- 1
Paste JSON API Response or Data Object
Input your JSON from REST APIs (GET /users), GraphQL queries, or configuration files. Paste multiple response samples to improve optional property detection accuracy.
- 2
AI Infers Swift Types and Generates Codable Structs
The AI analyzes property types (Int, String, Double, Bool), detects null values to generate optionals (String?), creates nested structs for sub-objects, and adds Codable conformance for automatic JSONDecoder compatibility.
- 3
Copy Production-Ready Swift Models
Receive Swift structs with proper type annotations, optional handling (? and !), CodingKeys for JSON key mapping (snake_case to camelCase), and nested struct definitions. Ready for immediate use with JSONDecoder in Xcode.
JSON vs Swift Codable: Type Safety Comparison
| Feature | JSON (Runtime) | Swift Codable (Compile-time) |
|---|---|---|
| Type Safety | Runtime only | Compile-time type checking |
| Null Handling | null value | Optional types (Type?) |
| Parsing | Manual dictionary access | Automatic Codable decoding |
| Validation | Runtime checks needed | Compiler enforced types |
| Refactoring | Error-prone | IDE-assisted, type-safe |
| API Contract | Implicit, undocumented | Explicit struct definition |
Code Examples
Example 1: Simple API Response to Codable Struct
{
"id": 123,
"username": "johndoe",
"email": "[email protected]",
"isVerified": true,
"lastLogin": null,
"roles": ["admin", "user"]
}struct User: Codable {
let id: Int
let username: String
let email: String
let isVerified: Bool
let lastLogin: String?
let roles: [String]
}
// Usage:
let decoder = JSONDecoder()
let user = try decoder.decode(User.self, from: jsonData)Key Changes:
JSON keys convert to Swift struct properties with camelCase naming conventions. The converter infers Int, String, Bool types from JSON values. Null values (lastLogin) generate optional types (String?) to handle missing data safely. Arrays become Swift typed arrays [String]. The struct conforms to Codable protocol, enabling automatic JSON decoding with JSONDecoder. No manual dictionary casting or type checking is needed—the compiler enforces type safety.
Example 2: Nested Objects with CodingKeys
{
"user_id": 456,
"display_name": "Jane Smith",
"profile": {
"age": 30,
"location": "San Francisco"
},
"preferences": {
"theme": "dark",
"notifications_enabled": true
}
}struct Profile: Codable {
let age: Int
let location: String
}
struct Preferences: Codable {
let theme: String
let notificationsEnabled: Bool
enum CodingKeys: String, CodingKey {
case theme
case notificationsEnabled = "notifications_enabled"
}
}
struct UserResponse: Codable {
let userId: Int
let displayName: String
let profile: Profile
let preferences: Preferences
enum CodingKeys: String, CodingKey {
case userId = "user_id"
case displayName = "display_name"
case profile, preferences
}
}Key Changes:
Nested JSON objects generate separate Swift structs (Profile, Preferences) that are referenced by type. Snake_case JSON keys (user_id, notifications_enabled) are mapped to Swift camelCase using CodingKeys enum. This allows JSON APIs with non-Swift naming to decode into idiomatic Swift code. Each nested level becomes a separate, reusable struct. The Codable protocol handles the entire hierarchy automatically, making complex API responses type-safe and easy to work with.
Frequently Asked Questions
The converter analyzes JSON samples to detect null values and missing keys, generating Swift optional types (String?) for nullable properties. If a property appears in all samples, it's marked as required (non-optional). For production use, validate against multiple API responses to ensure accurate optional inference. You can manually adjust property optionality based on API documentation.
No. All JSON to Swift conversion happens entirely client-side in your browser using JavaScript-based type inference. Your API responses—whether user data, financial records, or proprietary schemas—never leave your machine. The tool works offline once loaded.
Yes, but with limitations. Arrays with consistent object structures generate [ModelName] arrays. Mixed-type arrays (e.g., [{"type": "A"}, {"type": "B"}]) require manual refinement using Swift enums with associated values or protocol-based polymorphism. The converter generates a base type but complex polymorphic structures need custom Codable implementations.