JSON to Swift Converter

Why Generate Swift Structs from JSON?

Every iOS and macOS app that talks to an API eventually needs models that match the JSON it receives. Writing those structs by hand is slow and error prone: key names rarely follow Swift conventions, nested objects explode into multiple types, and a single wrong type breaks decoding at runtime with a cryptic error.

This converter reads a JSON sample and produces Swift Codable struct definitions that match its shape. Paste a response from your API, name the root type, and copy the generated code straight into Xcode.

How Types Are Mapped

Each JSON value is translated into the Swift type that decodes it correctly:

• Strings become String, whole numbers become Int, and decimal numbers become Double.
• Booleans become Bool.
• Arrays become Swift arrays typed to their element, such as [String] or [Product].
• Nested objects become separate named structs, so a nested address object turns into its own Address type referenced by the parent.
• Keys that are sometimes missing or null become optionals, so String? is used where data may be absent.

CodingKeys and Snake Case APIs

Swift style favors camelCase properties, but most APIs return snake_case keys like created_at or user_id. The generator follows that convention: user_id becomes a property named userId, and an explicit CodingKeys enum maps it back to the original JSON key. That means JSONDecoder works without any keyDecodingStrategy configuration, and the generated code is readable at the call site.

When every key is already a valid Swift identifier, no CodingKeys enum is emitted, keeping simple models compact.

Using the Generated Code

1. Paste a representative JSON sample. One object with realistic values is enough, and including optional fields helps the generator mark them optional.
2. Set the root struct name, for example WeatherResponse or UserProfile.
3. Copy the output into a Swift file in your project alongside your networking code.
4. Decode with try JSONDecoder().decode(WeatherResponse.self, from: data).

Structs are generated with let properties and value semantics, which matches Swift's recommendation for data models. If you need mutable models, change let to var after pasting.

Sample Data Tips

• Include one entry for every field, even if you have to add it by hand, so no column is missing from the output.
• Use the real value types from your API. A numeric ID that arrives as a string should stay a string in the sample.
• For arrays, one representative element is enough. The generator infers the element type from it.
• If a field is nullable in production, include a null value somewhere so it becomes optional.

Privacy

All parsing and code generation happens in your browser. API responses often contain tokens, user data, or internal identifiers, and none of it is uploaded, stored, or logged. The tool also works offline once the page has loaded.

Related Tools

Working with other languages or formats? These tools pair well with this converter:

• JSON to Kotlin
• JSON to TypeScript POJO Generator
• JSON to Java Converter
• JSON Formatter
• JSON Validator