JSON to Swift Codable

How to use it

1. Paste one response, or drop a .json file — the Swift pane refreshes as you type.
2. Open a tab per response variant: anything one variant omits comes back optional.
3. Choose the Swift side: type name, struct or class, access level, CodingKeys policy, protocols, Sendable, let or var, Int or Double.
4. Copy the source, save it as Models.swift, or share a permalink carrying every tab and setting.

Paste one response or several and read Swift back: a Codable struct per object shape, a CodingKeys enum holding the wire spelling of every key, and a question mark on anything a sample left out. Keys arrive as Swift names — user_id becomes userID — while the JSON side of the mapping stays byte-exact. Nothing is uploaded; the samples stay in this tab.

Examples

{"user_id":42,"avatar-url":"https://cdn.example/a.png","display_name":"Ada"}

import Foundation

// MARK: - Root
struct Root: Codable {
    let userID: Int
    let avatarURL: String
    let displayName: String

    enum CodingKeys: String, CodingKey {
        case userID = "user_id"
        case avatarURL = "avatar-url"
        case displayName = "display_name"
    }
}

{"id":1,"email":"ada@example.com","nickname":"ada"}

{"id":2,"email":"cy@example.com"}

import Foundation

// MARK: - Root
struct Root: Codable {
    let id: Int
    let email: String
    let nickname: String?

    enum CodingKeys: String, CodingKey {
        case id = "id"
        case email = "email"
        case nickname = "nickname"
    }
}

{"archived_at":null,"tags":[]}

import Foundation

// MARK: - Root
struct Root: Codable {
    let archivedAt: JSONNull?
    let tags: [JSONAny]

    enum CodingKeys: String, CodingKey {
        case archivedAt = "archived_at"
        case tags = "tags"
    }
}

Every example on this page is executed against the same engine that powers the tool, on every build.

Common errors

Sample 2: Unexpected "'" at line 1, column 2 — probable cause: single-quoted strings are JSON5, not JSON; use double quotes.

Every open tab must parse first. The tab number appears only while more than one is open, and the caret frame points at the byte that stopped the parser.

no Swift type could be generated — this JSON holds no object anywhere, so there are no properties to model; paste an object like {"id":1} or an array of objects

Codable models properties, and a bare list of numbers or a lone quoted string has none. Wrap the value in an object, or paste an array of objects — that shape generates, from the element up.

Input is larger than the 10 MB limit for this tool.

The tabs are weighed together before anything runs, and past the ceiling the run is refused rather than quietly truncated. Aim the command below at an export that large.

`snowflake` (/snowflake): 9223372036854775807 is beyond ±2^53 — the property is typed Double, which cannot hold every digit; decode it as String or Int64 by hand if the exact value matters

An advisory, not a failure: the model is generated. The digits were lost before any Swift type was chosen, because the sample crossed a JavaScript number on the way to the renderer.

`ratio` (/ratio): 1.0 is written as a float but its value is whole — the property is typed Int; add a sample with a fractional value to get Double

The mirror image of the previous line. A rate reading 1.0 in the tab you pasted looks integral, so add a fractional reading — or widen every integer — before a 0.5 arrives and the decode throws.

Keyboard shortcuts

⌘/Ctrl + Enter

Run the generator — required once the tabs pass 2 MB.

⌘/Ctrl + S

Write the Swift unit to a .swift file, not the page.

⌘/Ctrl + C

Copies the output pane when nothing is selected.

⌘/Ctrl + Shift + C

Copy the output despite an active selection.

t

Switch theme, unless a text field has focus.

? or ⌘/Ctrl + /

Show the shortcut overlay.

Esc

Close the topmost dialog.