PHP Best Practices

Introduction

Over the last 69 lessons, you have gone from your very first "Hello, World" to writing object-oriented PHP, talking to databases, handling authentication, and thinking about security and performance. This final lesson does not introduce a new PHP feature — instead, it ties everything together into the habits that separate working code from professional code.

None of these practices are complicated on their own. What makes them valuable is applying them consistently, on every project, until they become automatic.

Follow the PSR Standards

PSR (PHP Standards Recommendation) documents, published by the PHP-FIG group, define shared conventions that the wider PHP community has agreed on. Following them means your code looks familiar to any other PHP developer, and tools can rely on consistent structure.

<?php

namespace App\Services;

class InvoiceCalculator
{
    public function calculateTotal(array $items): float
    {
        $total = 0.0;

        foreach ($items as $item) {
            $total += $item['price'] * $item['quantity'];
        }

        return $total;
    }
}

Keep Functions and Classes Small

A function or class that tries to do too many things becomes hard to name, hard to test, and hard to change safely. The single responsibility principle says each piece of code should have one clear job.

function handleOrder(array $order): void
{
    // validates, calculates total, saves to database, and sends an email
    // all in one function — hard to test or reuse any single part
}

function validateOrder(array $order): bool { /* ... */ return true; }
function calculateOrderTotal(array $order): float { /* ... */ return 0.0; }
function saveOrder(array $order): int { /* ... */ return 1; }
function sendOrderConfirmation(int $orderId): void { /* ... */ }

function handleOrder(array $order): void
{
    if (!validateOrder($order)) {
        throw new InvalidArgumentException('Invalid order.');
    }

    $total = calculateOrderTotal($order);
    $orderId = saveOrder($order);
    sendOrderConfirmation($orderId);
}

Each smaller function can now be tested, reused, and understood on its own, while handleOrder() simply coordinates them — the same idea behind the Controller you saw in the MVC lesson.

Use Version Control for Every Project

Git should be part of every PHP project from the very first line of code, not added later once the project "matters." Version control gives you a complete history of changes, the ability to safely experiment on branches, and a way to collaborate with others without overwriting each other's work.

git init
git add .
git commit -m "Initial commit"

Write Readable Code, Not Clever Code

Code is read far more often than it is written. A short, clever one-liner might feel impressive, but if the next developer (often you, months later) has to puzzle over what it does, it has cost more time than it saved.

function sumEvenNumbers(array $numbers): int
{
    $sum = 0;

    foreach ($numbers as $number) {
        if ($number % 2 === 0) {
            $sum += $number;
        }
    }

    return $sum;
}

echo sumEvenNumbers([1, 2, 3, 4, 5, 6]);

12

Automated Testing with PHPUnit

This course has not covered automated testing in depth, but it is the natural next skill to develop after finishing it. PHPUnit is the standard testing framework for PHP, letting you write tests that call your functions with known inputs and automatically verify the output.

<?php

use PHPUnit\Framework\TestCase;

class InvoiceCalculatorTest extends TestCase
{
    public function testCalculatesTotalCorrectly(): void
    {
        $calculator = new \App\Services\InvoiceCalculator();

        $items = [
            ['price' => 10.00, 'quantity' => 2],
            ['price' => 5.00, 'quantity' => 1],
        ];

        $this->assertEquals(25.00, $calculator->calculateTotal($items));
    }
}

./vendor/bin/phpunit tests/InvoiceCalculatorTest.php

PHPUnit 10.5

.                                                                   1 / 1 (100%)

OK (1 test, 1 assertion)

Just like the automated tests you may have seen in other languages, PHPUnit tests give you confidence to change code later without fear of silently breaking something that used to work.

Validate Input at Every Boundary

A "boundary" is any point where data enters your application from outside: form submissions, query strings, API request bodies, file uploads, even data read from a database that another system wrote. Validating at every boundary — not just "somewhere" — closes the same gap that caused the security issues covered in the previous lessons.

function createUser(array $input): array
{
    $email = trim($input['email'] ?? '');
    $age = $input['age'] ?? null;

    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        throw new InvalidArgumentException('A valid email is required.');
    }

    if (!is_numeric($age) || $age < 0 || $age > 120) {
        throw new InvalidArgumentException('A valid age is required.');
    }

    return ['email' => $email, 'age' => (int) $age];
}

print_r(createUser(['email' => 'dev@example.com', 'age' => '29']));

Array
(
    [email] => dev@example.com
    [age] => 29
)

Common Mistakes

Best Practices Checklist

Frequently Asked Questions

Key Takeaways

Summary

Writing correct PHP is only part of becoming a capable PHP developer. Following shared standards, keeping code small and focused, using version control, naming things clearly, testing automatically, and validating input consistently are the habits that separate a working script from software other people can rely on and maintain.

What to Learn Next

Congratulations — you have reached the end of this 70-lesson PHP course! You have gone from your first script to variables, control flow, functions, object-oriented programming, error handling, working with databases, authentication, security, performance, and now professional best practices. That is a genuinely complete foundation in PHP.

Whichever direction you choose next, keep writing real code, keep applying what you have learned here, and keep building. That is how every PHP developer, no matter how experienced, continues to grow.