JSON to PHP Class Generator

What is JSON to PHP Class Generator?

PHP's built-in json_decode returns one of two very different things depending on its second argument: call json_decode($s) and you get a stdClass object with -> property access; call json_decode($s, true) and you get an associative array with [] access. Neither gives you type safety, IDE autocompletion, or a place to attach behavior. Converting JSON into a proper PHP class with typed properties solves all three, and that is what this generator does — it infers a PHP type for each field, builds a class with constructor and fromJson/toJson methods, and orders nested classes children-first so they are defined before use. The big shift in modern PHP is typed properties, added in PHP 7.4 and made far more ergonomic by constructor property promotion in PHP 8.0. Promotion lets you declare and assign a property in a single constructor parameter: public function __construct(public int $id, public ?string $name). The type declarations are enforced at runtime — assigning a string to an int property throws a TypeError — which turns a loosely typed array into a self-validating value object. The generator also offers a Laravel Eloquent mode. Eloquent models are not plain value objects; they extend the framework base class and lean on $fillable for mass-assignment protection and $casts to coerce database columns into the right PHP types. That is a different shape from a DTO, so the tool emits it separately.

How to Use

1. Set the class name and a namespace matching your PSR-4 autoload root (e.g. App\\DTO) so the file is discoverable by Composer
2. Choose PHP 8 constructor promotion for compact typed DTOs, or Laravel Eloquent mode if the data maps to a database model
3. Paste your JSON and click Generate — nullable JSON fields become ?type and arrays become typed array properties
4. Copy the output into a file named after the class (PSR-4 requires one class per file, filename matching class name)
5. For Eloquent mode, move the generated class into app/Models and confirm $casts matches your migration column types

Tips & Best Practices

• json_decode($s) returns stdClass (-> access) while json_decode($s, true) returns an associative array ([] access). Pick one convention project-wide; the generated fromJson assumes the associative-array form because it is easier to iterate and validate.
• Constructor promotion needs PHP 8.0+. On 7.4 you still get typed properties but must write the assignments by hand — the generator falls back automatically when you do not select promotion.
• A typed property with no default and no nullable marker is in an uninitialized state until assigned; reading it throws an Error, not null. Make optional fields ?type so a missing JSON key yields null instead of a fatal error.
• In Laravel, $casts controls how Eloquent converts a database column to a PHP type when you read $model->field. JSON booleans stored as tinyint columns need "field" => "boolean" in $casts or you will get 1/0 instead of true/false.
• Eloquent\u2019s $fillable is a security control, not a serialization hint: any column not listed there is silently ignored by Model::create() and ::fill(). If a field is not saving, check $fillable before anything else.

Frequently Asked Questions

Real-world Examples

{
  "id": 1024,
  "username": "marie",
  "verified": true,
  "avatarUrl": null,
  "score": 87.5
}

<?php

namespace App\DTO;

final class User
{
    public function __construct(
        public int $id,
        public string $username,
        public bool $verified,
        public ?string $avatarUrl,
        public float $score,
    ) {}

    public static function fromJson(array $data): self
    {
        return new self(
            id: $data['id'],
            username: $data['username'],
            verified: $data['verified'],
            avatarUrl: $data['avatarUrl'] ?? null,
            score: $data['score'],
        );
    }

    public function toJson(): array
    {
        return [
            'id' => $this->id,
            'username' => $this->username,
            'verified' => $this->verified,
            'avatarUrl' => $this->avatarUrl,
            'score' => $this->score,
        ];
    }
}

{
  "title": "Hello World",
  "published": true,
  "viewCount": 0,
  "rating": 4.2
}

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    protected $fillable = [
        'title',
        'published',
        'view_count',
        'rating',
    ];

    protected $casts = [
        'published' => 'boolean',
        'view_count' => 'integer',
        'rating' => 'float',
    ];
}

// $post = Post::create($request->validated());

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