The Problem

When your application communicates with external systems - APIs, message queues, event streams - you typically define data contracts using JSON Schema. On the PHP side, you represent those contracts as DTO classes with typed properties.

The problem is keeping both in sync. Every time the schema changes, you have to manually update the corresponding PHP class: rename properties, adjust types, add or remove fields. This is repetitive, error-prone, and easy to forget. The schema and the code silently drift apart, and type mismatches only surface at runtime.

The Solution

JSON Schema Codegen generates PHP DTO classes directly from your JSON Schema files. Run the generator after any schema change and your PHP classes are always up to date - no manual editing required.

The generator maps JSON Schema types to precise PHPDoc annotations that static analysis tools like PHPStan understand:

• "type": "string" → @var string
• "type": "string", "minLength": 1 → @var non-empty-string
• "type": "integer", "minimum": 0, "maximum": 100" → @var int<0, 100>
• "type": ["string", "null"] → @var string|null
• "type": "array", "items": {"type": "string"} → @var list<string>
• "oneOf": [{"$ref": "A.json"}, {"$ref": "B.json"}] → @var A|B
• "$ref": "Other.json" → @var Other

Requirements

• PHP 8.4+
• nette/php-generator: ^4.2 - used by the built-in generator implementation
• symfony/yaml: ^8.0 - optional, required only for YAML schema support

Installation

composer require guuzen/json-schema-codegen
composer require nette/php-generator

Quick Start

Create a PHP script that configures and runs the generator:

<?php

require 'vendor/autoload.php';

use Guuzen\JsonSchemaCodegen\Nette\NetteFilesGeneratorFactory;

NetteFilesGeneratorFactory::create(
    baseNamespace: 'App\Dto',
    schemaPath: '/path/to/schemas',
    outputPath: '/path/to/output',
    schemaSuffix: '.json',
    undefinedPath: 'Undefined.json',
)->run();

Run it with php generate.php whenever your schemas change.

Configuration

Option	Type	Description
baseNamespace	string	Root namespace for all generated classes
schemaPath	string	Absolute path to the directory containing your schema files
outputPath	string	Absolute path to the directory where generated PHP files are written
schemaSuffix	string	File extension used to identify schema files; also selects the decoder (.json or .yaml)
undefinedPath	string	Schema path (relative to schemaPath) representing an absent value, referenced by non-required properties so absence is distinguishable from null
typeMappings	array<string, class-string>	Optional. Maps a schema path (relative to schemaPath) to an existing class to reference instead of generating, e.g. ['DateTimeImmutable.json' => DateTimeImmutable::class]

Schema files in subdirectories of schemaPath produce classes in sub-namespaces. For example, schemas/billing/Address.json generates App\Dto\billing\Address.

Example

Given this schema at schemas/Product.json:

{
    "description": "A sellable product",
    "type": "object",
    "properties": {
        "name":      {"type": "string", "minLength": 1, "description": "The product name"},
        "stock":     {"type": "integer"},
        "quantity":  {"type": "integer", "minimum": 0, "maximum": 1000},
        "rating":    {"type": ["integer", "null"]},
        "price":     {"type": "number"},
        "tags":      {"type": "array", "items": {"type": "string"}},
        "externalId":{"type": ["integer", "string"]}
    }
}

The generator produces output/Product.php:

<?php

declare(strict_types=1);

namespace App\Dto;

/**
 * A sellable product
 */
final class Product
{
    public function __construct(
        /**
         * The product name
         *
         * @var non-empty-string
         */
        public $name,
        /**
         * @var int
         */
        public $stock,
        /**
         * @var int<0, 1000>
         */
        public $quantity,
        /**
         * @var int|null
         */
        public $rating,
        /**
         * @var float
         */
        public $price,
        /**
         * @var list<string>
         */
        public $tags,
        /**
         * @var int|string
         */
        public $externalId,
    ) {
    }
}

Cross-file references via $ref are also resolved. Given schemas/Order.json:

{
    "type": "object",
    "properties": {
        "customer": {"$ref": "Customer.json"},
        "note":     {"oneOf": [{"$ref": "Note.json"}, {"type": "null"}]},
        "items":    {"type": "array", "items": {"$ref": "OrderItem.json"}},
        "payment":  {"oneOf": [{"$ref": "CreditCardPayment.json"}, {"$ref": "BankTransferPayment.json"}]}
    }
}

The generator produces:

final class Order
{
    public function __construct(
        /** @var Customer */
        public $customer,
        /** @var Note|null */
        public $note,
        /** @var list<OrderItem> */
        public $items,
        /** @var CreditCardPayment|BankTransferPayment */
        public $payment,
    ) {
    }
}

YAML Support

YAML schema files are supported out of the box. Install symfony/yaml and set schemaSuffix to .yaml - create() selects the matching decoder from the suffix automatically:

composer require symfony/yaml

use Guuzen\JsonSchemaCodegen\Nette\NetteFilesGeneratorFactory;

NetteFilesGeneratorFactory::create(
    baseNamespace: 'App\Dto',
    schemaPath: '/path/to/schemas',
    outputPath: '/path/to/output',
    schemaSuffix: '.yaml',
    undefinedPath: 'Undefined.yaml',
)->run();

For full control, use NetteFilesGeneratorFactory::assemble(...) directly.

Running Tests

composer install
./vendor/bin/phpunit