Does it generate classes or structs?

Structs conforming to Codable, with let properties and nested model types. It imports Foundation.

When does it add CodingKeys?

When a property name changes, it emits a CodingKeys enum that maps Swift identifiers back to the original JSON keys.

How does it handle null?

Observed nulls and missing fields produce optional properties. Unknown or mixed values use a Codable JSONValue enum, added only when referenced.

Can I use JSONDecoder directly?

Yes. Copy the generated structs into your project and decode Root.self from Data. Review optional fields and date types first.

JSON to Swift Codable model generator

How to use this tool

Paste a representative response, including records whose fields differ.
Review the generated output and change the root name if needed.
Copy or download the code, then check the types against your API contract.

Worked example

This output comes from the built-in converter. The two item prices infer a floating-point field; the null and string notes infer a nullable field.

Input

{
  "user-id": 42,
  "profile": {
    "city": "London",
    "created_at": "2026-10-14T09:00:00Z"
  },
  "items": [
    {
      "price": 12,
      "note": null
    },
    {
      "price": 12.5,
      "note": "gift"
    }
  ]
}

Output

import Foundation

struct Root: Codable {
    let userId: Int
    let profile: Profile
    let items: [Item]

    enum CodingKeys: String, CodingKey {
        case userId = "user-id"
        case profile, items
    }
}

struct Profile: Codable {
    let city: String
    let createdAt: String

    enum CodingKeys: String, CodingKey {
        case city
        case createdAt = "created_at"
    }
}

struct Item: Codable {
    let price: Double
    let note: String?
}

Decode with JSONDecoder

Use JSONDecoder with the generated Root struct. Codable also supports encoding the same model with JSONEncoder.

Keep the default key strategy for this output. Its CodingKeys already contain wire names, including created_at.

let model = try JSONDecoder().decode(Root.self, from: responseData)
let encoded = try JSONEncoder().encode(model)

Options and edge cases

Integers infer Int, fractional values infer Double and integers beyond signed 64-bit range infer Decimal. Check target-platform limits and decimal precision.
Nulls or missing fields become optional properties. A null-only or mixed shape uses the generated JSONValue helper when needed.
JSONValue stores numbers as Double, so use explicit types for exact monetary values or very large IDs.
Date strings remain String. If you change a field to Date, configure JSONDecoder.dateDecodingStrategy for the API format.

Private by default

Your document stays in this browser. Tool Kumar parses, converts and creates downloads on your device, with no account or upload step.

JSON to Swift models questions

Does it generate classes or structs?: Structs conforming to Codable, with let properties and nested model types. It imports Foundation.
When does it add CodingKeys?: When a property name changes, it emits a CodingKeys enum that maps Swift identifiers back to the original JSON keys.
How does it handle null?: Observed nulls and missing fields produce optional properties. Unknown or mixed values use a Codable JSONValue enum, added only when referenced.
Can I use JSONDecoder directly?: Yes. Copy the generated structs into your project and decode Root.self from Data. Review optional fields and date types first.