Magento 2 Developer Core

This skill provides the foundational patterns all Magento 2 developers must follow. It covers architectural decisions, security, and best practices that apply to every part of a Magento project.

Related Skills

This is the foundation the other Magento 2 skills build on: magento2-frontend-dev and magento2-hyva-dev cover the two mutually exclusive theme stacks (check the theme's theme.xml parent to see which one the project actually uses, Luma vs Hyvä), magento2-backend-dev covers APIs/CLI/cron, and magento2-linter, magento2-security-scan, magento2-performance-audit verify the patterns below, magento2-code-review orchestrates all three (plus this skill's own anti-pattern checks) into one report scoped to a PR/module/theme/project. In a Govard environment, pair this with govard-magento for the container/CLI side.

Core Architectural Standards

Note: For framework-agnostic PHP (PSR-12/Composer/PDO) see php-dev-core. This skill covers Magento-specific DI/Repository/Plugin.

Dependency Injection (DI)

DO: Use Constructor Injection for all dependencies.

class MyService
{
    public function __construct(
        private readonly ProductRepositoryInterface $productRepository,
        private readonly LoggerInterface $logger
    ) {}

    public function getProduct(int $id): ?ProductInterface
    {
        return $this->productRepository->get($id);
    }
}

NEVER: Use ObjectManager::getInstance() (Service Locator anti-pattern).

// WRONG - Never do this
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$product = $objectManager->create(Product::class);

// CORRECT
public function __construct(ProductFactory $productFactory) {
    $this->productFactory = $productFactory;
}

Service Contracts

Always prefer interfaces in Api/ folders over concrete classes:

// WRONG
public function __construct(Product $product) { }

// CORRECT
public function __construct(ProductInterface $product) { }

Repositories

Always use repositories for data operations. Never call load(), save(), or delete() directly on models.

// WRONG
$product = $this->productFactory->create();
$product->load($id);

// CORRECT
$product = $this->productRepository->getById($id);

// WRONG
$this->productFactory->create()->save($product);

// CORRECT
$this->productRepository->save($product);

Plugins (Interceptors)

Prefer before and after plugins over around plugins:

// Prefer this pattern
public function beforeExecute(
    SaveProduct $subject,
    ProductInterface $product
): array {
    // Validate or modify $product before save
    return [$product];
}

// Instead of around plugins that wrap the entire method

Plugins only intercept public methods, must be stateless, and should not target a module's own classes or data objects. Register them in di.xml with an explicit sortOrder when order matters. Observer order is not guaranteed by contrast, if the sequence matters, use a plugin instead of an observer. Before adding a new plugin or observer, check for existing ones on the same target class/event, magento2-code-review's plugin/observer conflict check (references/plugin-observer-conflict-check.md in that skill) covers the grep procedure.

Declarative Schema

Use db_schema.xml for all database changes. Never modify database directly:

<!-- app/code/Vendor/Module/etc/db_schema.xml -->
<?xml version="1.0"?>
<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="vendor_module_custom_table" resource="default">
        <column xsi:type="int" name="id" padding="10" unsigned="true" nullable="false" identity="true"/>
        <column xsi:type="varchar" name="name" nullable="false" length="255"/>
        <column xsi:type="timestamp" name="created_at" nullable="false" init="current"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id"/>
        </constraint>
    </table>
</schema>

Coding Standards

PHPCS (Magento2 Ruleset)

PHPStan Requirements

Always run PHPStan at level 6+ using bitexpert/phpstan-magento for Magento's magic classes.

# In a Govard environment
govard sh -c "vendor/bin/phpstan analyse app/code -c phpstan.neon"

Strict Typing

Always include at the top of new PHP files:

<?php
declare(strict_types=1);

Security Standards

No Superglobals

NEVER use $_GET, $_POST, $_REQUEST, $_SESSION, $_COOKIE directly.

// WRONG
$id = $_GET['id'];

// CORRECT - Use RequestInterface
public function __construct(
    private readonly \Magento\Framework\App\RequestInterface $request
) {}

$id = (int) $this->request->getParam('id');

XSS Prevention

Always escape output in templates:

// HTML content
<?= $escaper->escapeHtml($userInput) ?>

// HTML attributes
<div data-id="<?= $escaper->escapeHtmlAttr($id) ?>">

// JavaScript strings
<script>var name = '<?= $escaper->escapeJs($productName) ?>';</script>

// URLs
<a href="<?= $escaper->escapeUrl($url) ?>">

// CSS values
<div style="color: <?= $escaper->escapeCss($color) ?>">

The Magento2.Security.XssTemplate PHPCS sniff treats any method whose name contains html (e.g. getLabelHtml()) as already safe, do not wrap it in escapeHtml() again, that double-escapes the output.

CSRF Protection

Include form key in all forms:

<form action="<?= $escaper->escapeUrl($block->getSubmitUrl()) ?>" method="post">
    <?= $block->getBlockHtml('formkey') ?>
</form>

Discouraged Functions

Use Magento wrappers instead of native PHP:

Verification Workflow

Run these checks before completing any backend task:

# 1. PHPCS Linting
vendor/bin/phpcs --standard=Magento2 app/code/Vendor/Module

# 2. PHPStan Analysis
vendor/bin/phpstan analyse app/code/Vendor/Module -c phpstan.neon

# 3. DI Compilation
bin/magento setup:di:compile

# 4. Flush cache
bin/magento cache:flush

Usage Patterns

Creating a Module

Otherwise: manually verify registration.php, etc/module.xml sequence, and each etc/*.xml parses.

1. Create registration file: app/code/Vendor/Module/registration.php
2. Create etc/module.xml with correct sequence
3. Define etc/di.xml for preferences and plugins
4. Use db_schema.xml for database schema
5. Run bin/magento module:enable Vendor_Module

CLI Commands

// etc/di.xml
<type name="Magento\Framework\Console\CommandList">
    <arguments>
        <argument name="commands" xsi:type="array">
            <item name="vendor_module_sync" xsi:type="object">Vendor\Module\Console\Command\SyncCommand</item>
        </argument>
    </arguments>
</type>

Cron Jobs

<!-- etc/crontab.xml -->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Cron:etc/crontab.xsd">
    <group id="default">
        <job name="vendor_module_cleanup" instance="Vendor\Module\Cron\Cleanup" method="execute">
            <schedule>0 2 * * *</schedule>
        </job>
    </group>
</config>

Configuration File Reference

Quick lookup for what each etc/ XML file controls:

Rule of thumb: stale data is an indexer problem (check indexer:status); stale output is a cache problem (cache:clean/cache:flush). Diagnose in that order rather than assuming a cache bug.

Anti-Pattern Severity (for code review)

Full severity scale and stable finding codes (shared with magento2-linter, magento2-security-scan, magento2-performance-audit, and magento2-code-review): references/severity-and-codes.md. The architecture anti-patterns this skill defines are catalogued there under the M2-ARCH-xxx namespace, map a new finding to an existing code before minting a new one.

Testing Conventions

• Unit tests (Test/Unit/): typed mocks only, never ObjectManager::getInstance(), never test private methods via reflection, if a private method needs its own test, it belongs in its own class.
• Integration tests (Test/Integration/): use Bootstrap::getObjectManager(), load data with @magentoDataFixture fixture files rather than creating entities inline, and annotate with @magentoDbIsolation so tests don't leak state between each other.
• Functional tests: MFTF (Magento Functional Testing Framework) for full user-journey coverage.

References

For detailed patterns, see:

• references/coding-standards.md - Extended PHPCS/PHPStan guide
• references/architecture-patterns.md - Service contracts, repositories, plugins
• references/security-best-practices.md - Security checklist and patterns
• references/severity-and-codes.md - Shared severity scale and finding codes (used by the whole QA quartet)