PHP Development

PHP Development

Optimized for current PHP 8.x releases, PHPUnit 11+, Composer 2.x, and PDO-backed MySQL or MariaDB apps.

Expert guidance for building high-quality PHP applications with PHP 8.0+, PDO for secure database access, RESTful API design, and XAMPP environment configuration following official PHP documentation at https://php.net.

• Leverage native parallel subagent dispatch and 200k+ context windows where available.

Anti-Patterns

• Interpolating SQL directly: Prepared statements are the baseline for correctness and security in PHP data access.
• Mixing request parsing, business rules, and rendering: Tightly coupled scripts are harder to test and evolve into APIs.
• Assuming validation alone prevents XSS: Output encoding still matters when user-controlled content is rendered back to HTML.

Verification Protocol

Before claiming "skill applied successfully":

1. Pass/fail: The PHP Development implementation names the target runtime, framework version, and affected files.
2. Pass/fail: Build, lint, test, or equivalent local validation is run for the changed surface.
3. Pass/fail: Edge cases for errors, dependency drift, and environment differences are addressed or explicitly out of scope.
4. Pressure-test scenario: Apply the workflow to a change that passes happy-path tests but fails one boundary condition.
5. Success metric: Zero untested success claims; every implementation claim maps to a command or artifact.

Before and After Example

<?php
// Before
$stmt = $pdo->query("SELECT * FROM users WHERE email = '$email'");
$user = $stmt->fetch();

// After
$stmt = $pdo->prepare('SELECT id, email, password_hash FROM users WHERE email = :email LIMIT 1');
$stmt->execute(['email' => $email]);
$user = $stmt->fetch(PDO::FETCH_ASSOC);

Replaces string interpolation with a prepared statement and a narrower result shape.

Activation Conditions

Use symptom -> action triggers: when one matches, apply this skill and verify with the protocol below.

Core PHP Development:

• Building PHP RESTful APIs with proper HTTP methods
• Working with XAMPP (Apache + MySQL + PHP) environment
• Implementing secure database operations with PDO
• Creating authentication and session management systems
• Handling file uploads and form submissions

Database & Data Layer:

• Connecting PHP to MySQL/MariaDB with PDO
• Writing prepared statements to prevent SQL injection
• Implementing transaction handling for data integrity
• Creating repository patterns for data access
• Working with MySQLi vs PDO comparisons

Security & Best Practices:

• Implementing password hashing (password_hash, password_verify)
• Securing against XSS, CSRF, and SQL injection
• Validating and sanitizing user input
• Managing sessions and authentication tokens
• Configuring CORS headers for API access

API Development:

• Designing RESTful endpoints with proper HTTP status codes
• Handling JSON requests and responses
• Implementing middleware for authentication and authorization
• Error handling and logging
• Rate limiting and API versioning

Part 1: PHP 8.0+ Fundamentals

Modern PHP Features

<?php
// Named arguments (PHP 8.0+)
function createUser(string $name, string $email, bool $isAdmin = false): User {
    return new User($name, $email, $isAdmin);
}

// Call with named arguments
$user = createUser(email: 'user@example.com', name: 'John Doe');

// Union types (PHP 8.0+)
function processValue(string|int|float $value): string {
    return (string)$value;
}

// Nullsafe operator (PHP 8.0+)
$country = $session?->user?->address?->country ?? 'Unknown';

// Constructor property promotion (PHP 8.0+)
class User {
    public function __construct(
        public string $name,
        public string $email,
        private string $passwordHash
    ) {}
}

Type Declarations & Strict Types

<?php
declare(strict_types=1); // Enforce type safety

// Typed properties and return types
class Recipe {
    private int $id;
    private string $title;
    private ?DateTime $createdAt;

    public function __construct(int $id, string $title) {
        $this->id = $id;
        $this->title = $title;
    }

    public function getTitle(): string {
        return $this->title;
    }

    public function setCreatedAt(?DateTime $date): void {
        $this->createdAt = $date;
    }
}

// Union and intersection types
function processData(string|array $data): string|int {
    return is_array($data) ? count($data) : strlen($data);
}

Part 2: PDO Database Integration

Database Connection Class

<?php
class Database {
    private static ?PDO $instance = null;

    public static function getInstance(): PDO {
        if (self::$instance === null) {
            $host = $_ENV['DB_HOST'] ?? 'localhost';
            $dbname = $_ENV['DB_NAME'] ?? 'recipe_sharing_system';
            $username = $_ENV['DB_USER'] ?? 'root';
            $password = $_ENV['DB_PASSWORD'] ?? '';
            $charset = 'utf8mb4';

            $dsn = "mysql:host=$host;dbname=$dbname;charset=$charset";

            try {
                self::$instance = new PDO($dsn, $username, $password, [
                    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
                    PDO::ATTR_EMULATE_PREPARES => false,
                ]);
            } catch (PDOException $e) {
                error_log("Database connection failed: " . $e->getMessage());
                throw new RuntimeException("Database connection error");
            }
        }

        return self::$instance;
    }
}

Prepared Statements for Security

<?php
class UserRepository {
    private PDO $db;

    public function __construct(PDO $db) {
        $this->db = $db;
    }

    // Find user by email with prepared statement
    public function findByEmail(string $email): ?array {
        $stmt = $this->db->prepare(
            "SELECT id, email, password_hash, role, status
             FROM user
             WHERE email = :email LIMIT 1"
        );

        $stmt->bindParam(':email', $email, PDO::PARAM_STR);
        $stmt->execute();

        $user = $stmt->fetch();
        return $user ?: null;
    }

    // Create new user with password hashing
    public function create(string $name, string $email, string $password): int {
        $passwordHash = password_hash($password, PASSWORD_DEFAULT);

        $stmt = $this->db->prepare(
            "INSERT INTO user (name, email, password_hash, role, status, created_at, updated_at)
             VALUES (:name, :email, :password_hash, 'user', 'active', NOW(), NOW())"
        );

        $stmt->bindParam(':name', $name, PDO::PARAM_STR);
        $stmt->bindParam(':email', $email, PDO::PARAM_STR);
        $stmt->bindParam(':password_hash', $passwordHash, PDO::PARAM_STR);

        $stmt->execute();

        return (int) $this->db->lastInsertId();
    }

    // Authentication with password verification
    public function authenticate(string $email, string $password): ?array {
        $user = $this->findByEmail($email);

        if ($user === null) {
            return null;
        }

        if (!password_verify($password, $user['password_hash'])) {
            return null;
        }

        // Check if password needs rehash
        if (password_needs_rehash($user['password_hash'], PASSWORD_DEFAULT)) {
            $newHash = password_hash($password, PASSWORD_DEFAULT);
            $this->updatePasswordHash($user['id'], $newHash);
        }

        unset($user['password_hash']); // Remove sensitive data
        return $user;
    }

    private function updatePasswordHash(int $userId, string $hash): void {
        $stmt = $this->db->prepare(
            "UPDATE user SET password_hash = :hash WHERE id = :id"
        );
        $stmt->execute([':hash' => $hash, ':id' => $userId]);
    }
}

Transaction Management

<?php
class RecipeService {
    private PDO $db;

    public function __construct(PDO $db) {
        $this->db = $db;
    }

    // Create recipe with ingredients, instructions, and images in a transaction
    public function createRecipeWithDetails(array $recipeData, array $ingredients, array $instructions): int {
        try {
            $this->db->beginTransaction();

            // Insert recipe
            $stmt = $this->db->prepare(
                "INSERT INTO recipe (title, description, category, difficulty, prep_time, cook_time, servings, author_id, status, created_at, updated_at)
                 VALUES (:title, :description, :category, :difficulty, :prep_time, :cook_time, :servings, :author_id, 'pending', NOW(), NOW())"
            );

            $stmt->execute([
                ':title' => $recipeData['title'],
                ':description' => $recipeData['description'],
                ':category' => $recipeData['category'],
                ':difficulty' => $recipeData['difficulty'],
                ':prep_time' => $recipeData['prepTime'],
                ':cook_time' => $recipeData['cookTime'],
                ':servings' => $recipeData['servings'],
                ':author_id' => $recipeData['authorId'],
            ]);

            $recipeId = (int) $this->db->lastInsertId();

            // Insert ingredients
            $ingredientStmt = $this->db->prepare(
                "INSERT INTO ingredient (recipe_id, name, quantity, unit, sort_order, created_at, updated_at)
                 VALUES (:recipe_id, :name, :quantity, :unit, :sort_order, NOW(), NOW())"
            );

            foreach ($ingredients as $index => $ingredient) {
                $ingredientStmt->execute([
                    ':recipe_id' => $recipeId,
                    ':name' => $ingredient['name'],
                    ':quantity' => $ingredient['quantity'],
                    ':unit' => $ingredient['unit'],
                    ':sort_order' => $index,
                ]);
            }

            // Insert instructions
            $instructionStmt = $this->db->prepare(
                "INSERT INTO instruction (recipe_id, step_number, instruction_text, created_at, updated_at)
                 VALUES (:recipe_id, :step_number, :instruction_text, NOW(), NOW())"
            );

            foreach ($instructions as $index => $instruction) {
                $instructionStmt->execute([
                    ':recipe_id' => $recipeId,
                    ':step_number' => $index + 1,
                    ':instruction_text' => $instruction['text'],
                ]);
            }

            $this->db->commit();

            return $recipeId;

        } catch (Exception $e) {
            $this->db->rollBack();
            error_log("Failed to create recipe: " . $e->getMessage());
            throw $e;
        }
    }
}

Part 3: RESTful API Development

JSON Response Helpers

<?php
class Response {
    public static function json(mixed $data, int $statusCode = 200): never {
        http_response_code($statusCode);
        header('Content-Type: application/json; charset=utf-8');
        echo json_encode($data, JSON_THROW_ON_ERROR | JSON_UNESCAPED_SLASHES);
        exit;
    }

    public static function error(string $message, int $statusCode = 400): never {
        self::json([
            'success' => false,
            'error' => $message,
        ], $statusCode);
    }

    public static function success(mixed $data = null, string $message = 'Success'): never {
        self::json([
            'success' => true,
            'message' => $message,
            'data' => $data,
        ]);
    }
}

CORS Middleware

<?php
// Handle CORS headers
$allowedOrigins = [
    'http://localhost:5173', // Vite dev server
    'http://localhost:3000',  // Alternative dev server
];

$origin = $_SERVER['HTTP_ORIGIN'] ?? '';

if (in_array($origin, $allowedOrigins, true)) {
    header("Access-Control-Allow-Origin: $origin");
}

header('Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS');
header('Access-Control-Allow-Headers: Content-Type, Authorization');
header('Access-Control-Allow-Credentials: true');

// Handle preflight requests
if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    http_response_code(200);
    exit;
}

Authentication Middleware

<?php
function requireAuth(): array {
    $authHeader = $_SERVER['HTTP_AUTHORIZATION'] ?? '';

    if (!preg_match('/Bearer\s+(.*)$/i', $authHeader, $matches)) {
        Response::error('Unauthorized: Missing or invalid token', 401);
    }

    $token = $matches[1];

    // Validate token (example withJWT)
    try {
        $payload = JWT::decode($token, $_ENV['JWT_SECRET'], ['HS256']);
        return (array) $payload;
    } catch (Exception $e) {
        Response::error('Unauthorized: Invalid token', 401);
    }
}

function requireAdmin(): array {
    $user = requireAuth();

    if ($user['role'] !== 'admin') {
        Response::error('Forbidden: Admin access required', 403);
    }

    return $user;
}

API Controller Example

<?php
require_once '../../config/database.php';
require_once '../../middleware/cors.php';
require_once '../../utils/response.php';

class RecipeController {
    private PDO $db;

    public function __construct() {
        $this->db = Database::getInstance();
    }

    // GET /api/recipes - Get all published recipes
    public function index(): void {
        $category = $_GET['category'] ?? null;
        $difficulty = $_GET['difficulty'] ?? null;
        $search = $_GET['search'] ?? null;
        $limit = (int)($_GET['limit'] ?? 20);
        $offset = (int)($_GET['offset'] ?? 0);

        $query = "SELECT r.*, u.name as author_name,
                         COUNT(DISTINCT rv.id) as view_count,
                         COUNT(DISTINCT lr.id) as like_count,
                         AVG(rev.rating) as average_rating
                  FROM recipe r
                  JOIN user u ON r.author_id = u.id
                  LEFT JOIN recipe_view rv ON r.id = rv.recipe_id
                  LEFT JOIN like_record lr ON r.id = lr.recipe_id
                  LEFT JOIN review rev ON r.id = rev.recipe_id
                  WHERE r.status = 'published'";

        $params = [];

        if ($category !== null) {
            $query .= " AND r.category = :category";
            $params[':category'] = $category;
        }

        if ($difficulty !== null) {
            $query .= " AND r.difficulty = :difficulty";
            $params[':difficulty'] = $difficulty;
        }

        if ($search !== null) {
            $query .= " AND (r.title LIKE :search OR r.description LIKE :search)";
            $searchTerm = "%$search%";
            $params[':search'] = $searchTerm;
            $params[':search2'] = $searchTerm;
        }

        $query .= " GROUP BY r.id ORDER BY r.created_at DESC LIMIT :limit OFFSET :offset";

        $stmt = $this->db->prepare($query);
        $stmt->execute($params);

        $recipes = $stmt->fetchAll();

        Response::success($recipes);
    }

    // GET /api/recipes/:id - Get recipe by ID
    public function show(int $id): void {
        $stmt = $this->db->prepare(
            "SELECT r.*, u.name as author_name, u.email as author_email,
                    GROUP_CONCAT(CONCAT(i.name, ' (', i.quantity, ' ', i.unit, ')') SEPARATOR ', ') as ingredients
             FROM recipe r
             JOIN user u ON r.author_id = u.id
             LEFT JOIN ingredient i ON r.id = i.recipe_id
             WHERE r.id = :id
             GROUP BY r.id"
        );

        $stmt->execute([':id' => $id]);
        $recipe = $stmt->fetch();

        if ($recipe === false) {
            Response::error('Recipe not found', 404);
        }

        // Fetch instructions
        $instStmt = $this->db->prepare(
            "SELECT step_number, instruction_text
             FROM instruction
             WHERE recipe_id = :recipe_id
             ORDER BY step_number"
        );

        $instStmt->execute([':recipe_id' => $id]);
        $recipe['instructions'] = $instStmt->fetchAll();

        Response::success($recipe);
    }

    // POST /api/recipes - Create new recipe
    public function store(): void {
        $user = requireAuth();
        $data = json_decode(file_get_contents('php://input'), true);

        // Validate required fields
        if (empty($data['title']) || empty($data['description'])) {
            Response::error('Title and description are required');
        }

        $recipeData = [
            'title' => $data['title'],
            'description' => $data['description'],
            'category' => $data['category'] ?? 'Uncategorized',
            'difficulty' => $data['difficulty'] ?? 'Medium',
            'prepTime' => (int)($data['prepTime'] ?? 0),
            'cookTime' => (int)($data['cookTime'] ?? 0),
            'servings' => (int)($data['servings'] ?? 1),
            'authorId' => $user['id'],
        ];

        $recipeService = new RecipeService($this->db);

        try {
            $recipeId = $recipeService->createRecipeWithDetails(
                $recipeData,
                $data['ingredients'] ?? [],
                $data['instructions'] ?? []
            );

            Response::success(['id' => $recipeId], 'Recipe created successfully', 201);
        } catch (Exception $e) {
            Response::error('Failed to create recipe: ' . $e->getMessage(), 500);
        }
    }
}

Part 4: Input Validation & Sanitization

Validation Functions

<?php
class Validator {
    public static function email(string $email): bool {
        return filter_var($email, FILTER_VALIDATE_EMAIL) !== false;
    }

    public static function string(string $value, int $min = 1, int $max = 255): bool {
        $length = strlen($value);
        return $length >= $min && $length <= $max;
    }

    public static function integer(int $value, int $min = PHP_INT_MIN, int $max = PHP_INT_MAX): bool {
        return $value >= $min && $value <= $max;
    }

    public static function enum(string $value, array $allowed): bool {
        return in_array($value, $allowed, true);
    }

    public static function required(array $data, array $fields): array {
        $errors = [];
        foreach ($fields as $field) {
            if (empty($data[$field])) {
                $errors[] = "$field is required";
            }
        }
        return $errors;
    }

    public static function sanitize(string $input): string {
        return htmlspecialchars(trim($input), ENT_QUOTES, 'UTF-8');
    }
}

Validation Example

<?php
function validateRecipeData(array $data): array {
    $errors = [];

    // Validate title
    if (empty($data['title'])) {
        $errors[] = 'Title is required';
    } elseif (!Validator::string($data['title'], 3, 200)) {
        $errors[] = 'Title must be between 3 and 200 characters';
    }

    // Validate email
    if (!empty($data['email']) && !Validator::email($data['email'])) {
        $errors[] = 'Invalid email address';
    }

    // Validate rating
    if (isset($data['rating']) && !Validator::integer((int)$data['rating'], 1, 5)) {
        $errors[] = 'Rating must be between 1 and 5';
    }

    // Validate difficulty
    if (!empty($data['difficulty']) &&
        !Validator::enum($data['difficulty'], ['Easy', 'Medium', 'Hard'])) {
        $errors[] = 'Difficulty must be Easy, Medium, or Hard';
    }

    // Sanitize all string inputs
    foreach ($data as $key => $value) {
        if (is_string($value)) {
            $data[$key] = Validator::sanitize($value);
        }
    }

    return ['errors' => $errors, 'data' => $data];
}

Part 5: Security Best Practices

Password Management

<?php
class PasswordManager {
    public static function hash(string $password): string {
        // Use algorithm recommended by PHP
        return password_hash($password, PASSWORD_DEFAULT);
    }

    public static function verify(string $password, string $hash): bool {
        return password_verify($password, $hash);
    }

    public static function needsRehash(string $hash): bool {
        return password_needs_rehash($hash, PASSWORD_DEFAULT);
    }

    public static function validateStrength(string $password): array {
        $errors = [];

        if (strlen($password) < 8) {
            $errors[] = 'Password must be at least 8 characters';
        }

        if (!preg_match('/[A-Z]/', $password)) {
            $errors[] = 'Password must contain at least one uppercase letter';
        }

        if (!preg_match('/[a-z]/', $password)) {
            $errors[] = 'Password must contain at least one lowercase letter';
        }

        if (!preg_match('/[0-9]/', $password)) {
            $errors[] = 'Password must contain at least one number';
        }

        if (!preg_match('/[!@#$%^&*(),.?":{}|<>]/', $password)) {
            $errors[] = 'Password must contain at least one special character';
        }

        return $errors;
    }
}

Session Management

<?php
class Session {
    public static function start(): void {
        if (session_status() === PHP_SESSION_NONE) {
            session_start();
        }
    }

    public static function set(string $key, mixed $value): void {
        $_SESSION[$key] = $value;
    }

    public static function get(string $key, mixed $default = null): mixed {
        return $_SESSION[$key] ?? $default;
    }

    public static function remove(string $key): void {
        unset($_SESSION[$key]);
    }

    public static function destroy(): void {
        $_SESSION = [];
        session_destroy();
        if (ini_get("session.use_cookies")) {
            $params = session_get_cookie_params();
            setcookie(session_name(), '', time() - 42000,
                $params["path"], $params["domain"],
                $params["secure"], $params["httponly"]
            );
        }
    }

    public static function regenerateId(): void {
        session_regenerate_id(true);
    }
}

CSRF Protection

<?php
class CsrfProtection {
    public static function generateToken(): string {
        if (!isset($_SESSION['csrf_token'])) {
            $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
        }
        return $_SESSION['csrf_token'];
    }

    public static function validateToken(string $token): bool {
        return isset($_SESSION['csrf_token']) &&
               hash_equals($_SESSION['csrf_token'], $token);
    }

    public static function invalidateToken(): void {
        unset($_SESSION['csrf_token']);
    }

    public static function getInputField(): string {
        $token = self::generateToken();
        return "<input type='hidden' name='csrf_token' value='$token'>";
    }
}

Part 6: XAMPP Configuration

.htaccess for URL Rewriting

RewriteEngine On

# Redirect trailing slashes
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} (.+)/$
RewriteRule ^ %1 [L,R=301]

# Handle API routes
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^api/(.*)$ api/index.php [QSA,L]

# Handle frontend routes (SPA)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.html [QSA,L]

PHP Configuration (php.ini)

; Enable error reporting for development
error_reporting = E_ALL
display_errors = On
display_startup_errors = On

; Log errors in production
log_errors = On
error_log = "C:/xampp/php/logs/php_error.log"

; Increase upload limits
upload_max_filesize = 10M
post_max_size = 10M

; Enable PDO extensions
extension=pdo_mysql
extension=mysqli

; Enable session handling
session.save_handler = files
session.save_path = "C:/xampp/tmp"
session.use_strict_mode = 1
session.cookie_httponly = 1
session.cookie_secure = 0  ; Set to 1 if HTTPS
session.use_only_cookies = 1

; Set timezone
date.timezone = "Asia/Bangkok"

PHP Development Best Practices

Code Style (PSR-12)

• Use strict types (declare(strict_types=1))
• Follow PSR-12 coding standards
• Use type hints for all functions and methods
• Use namespaces for autoloading classes
• Exception handling with try-catch blocks

Security

• Always use prepared statements with PDO
• Hash passwords with password_hash()
• Validate all user input
• Sanitize output for XSS prevention
• Use HTTPS in production
• Implement CSRF protection

API Design

• Use proper HTTP status codes (200, 201, 400, 401, 403, 404, 500)
• Return JSON responses
• Handle CORS headers
• Implement authentication middleware
• Rate limit endpoints

Database

• Use PDO for database connections
• Implement transactions for multi-step operations
• Use named parameters in prepared statements
• Handle connection errors gracefully
• Close connections properly

Common Pitfalls

• Interpolating SQL directly: Prepared statements are the baseline for correctness and security in PHP data access.
• Mixing request parsing, business rules, and rendering: Tightly coupled scripts become difficult to test or migrate into APIs.
• Ignoring output encoding: Input validation alone does not protect against XSS when data is rendered back to users.

References & Resources

Documentation

• PHP 8.4+ API Patterns — Modern PHP API development patterns

Examples

• PDO Database Patterns — PHP PDO database integration examples

Scripts

• XAMPP Setup Script — PowerShell script to configure XAMPP for PHP development

Official Documentation

• PHP Manual — Complete PHP reference
• PDO for MySQL — PDO MySQL driver documentation
• Password Hashing — Secure password functions
• REST API Best Practices — API design principles

PHP Standards

• PSR-12: Extended Coding Style — Modern PHP coding style
• XAMPP Documentation — XAMPP setup and configuration

Security Resources

• OWASP PHP Security — XSS prevention
• SQL Injection Prevention — SQL injection prevention
• PHP Security Guide — Official PHP security considerations

Cross-Client Portability

This skill is written to stay usable across GitHub Copilot, Claude Code, and Codex.

• GitHub Copilot: keep the folder in a Copilot-visible skill path or wrap the workflow in project instructions when folder discovery is unavailable.
• Claude Code: keep the folder in a local skills directory or a compatible plugin source.
• Codex: install or sync the folder into $CODEX_HOME/skills/php-development and restart Codex after major changes.

MCP Availability And Fallback

Preferred MCP Server: None required

• Fallback prompt: "Use the PHP Development skill without MCP. Rely on the local SKILL.md, bundled references or scripts, and manual verification. Show the exact commands, evidence, and final checks you used before concluding."
• If the current host does not expose a matching server, use the bundled references, scripts, native toolchain, and manual workflow already described in this skill.
• Treat direct local verification, rendered output, logs, tests, or screenshots as the fallback evidence path before completion.

Related Skills

• sql-development: Use it when the workflow also needs SQL query, schema, and performance tuning work.
• code-quality: Use it when the workflow also needs two-stage review (spec compliance first, then code quality), maintainability, and refactoring guidance.
• systematic-debugging: Use it when the workflow also needs root-cause debugging before proposing fixes.
• development-workflow: Use it when the workflow also needs planning, quality gates, and delivery tracking.