35 Interview questions to ask while hiring a PHP developer 

The demand for PHP developers remains robust, reflecting the language’s enduring popularity and essential role in web development. As of 2024, PHP powers approximately 79.2% of all websites, a testament to its widespread adoption and relevance. A significant contributor to this dominance is WordPress, which itself supports 40% of the web, underscoring PHP’s integral position in content management systems (CMS) like WordPress, Joomla, and Drupal​​.

The job market for PHP developers is also promising, with competitive salaries and numerous opportunities. The average annual salary for a PHP developer is around $91,010, with top earners making up to $122,000. This compensation reflects the high demand for skilled professionals capable of leveraging PHP’s capabilities in building dynamic and scalable web applications​​. Furthermore, the Bureau of Labor Statistics projects a 16% growth in web developer employment from 2022 to 2032, significantly faster than the average for all occupations, adding approximately 34,700 new jobs each year​.

For HR professionals and CXOs, these statistics highlight the critical need for thorough and strategic hiring processes when recruiting PHP developers. Ensuring candidates possess the right blend of technical expertise, problem-solving abilities, and adaptability to emerging technologies is vital for maintaining a competitive edge in the digital landscape.

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Why use skills assessments for assessing php developer candidates?

Using skills assessments is a strategic approach to ensure you hire the most qualified PHP developers. These assessments objectively measure a candidate’s coding abilities and knowledge of various essential skills, helping you make data-driven hiring decisions. They offer a clear picture of a candidate’s proficiency, reducing the reliance on self-reported skills and subjective evaluations during PHP Developer interview questions.

Platforms like Testlify offer comprehensive assessments tailored to evaluate PHP developers. These assessments cover various topics, from fundamental coding skills to advanced PHP frameworks and tools. By incorporating skills assessments into your hiring process, you can identify candidates with theoretical knowledge and practical expertise in solving real-world problems.

Implementing these assessments helps streamline the recruitment process, saving time and resources by quickly filtering out unsuitable candidates. This ensures that only the most capable and skilled developers move forward in the hiring pipeline, ultimately contributing to building a stronger, more competent development team. Using skills assessments alongside PHP Developer interview questions enhances the overall evaluation process, ensuring you hire the best talent available.

Recruit Smarter: Looking to discover talent like a pro? Check out testlify’s PHP Developer test.

When should you ask these questions in the hiring process?

Incorporating PHP Developer interview questions at different stages of the hiring process ensures a comprehensive evaluation of a candidate’s skills. During the initial screening phase, basic PHP-related questions can help assess a candidate’s fundamental understanding of the language. This helps to quickly identify whether they possess the necessary baseline knowledge to move forward in the hiring process.

As candidates progress to the technical interview stage, more detailed and challenging PHP Developer interview questions should be used. This is the ideal time to evaluate their problem-solving abilities, coding proficiency, and familiarity with advanced PHP frameworks and tools. Asking them to solve real-world problems or to complete coding tasks can provide valuable insights into their practical skills and approach to coding challenges.

In the final interview rounds, focus on more complex scenarios and integrate questions that assess soft skills, such as teamwork, communication, and adaptability. This comprehensive approach, using PHP Developer interview questions throughout the hiring process, ensures that you select a candidate who not only meets the technical requirements but also fits well within your team and organizational culture.

General PHP developer interview questions to ask applicants

Interviewing PHP developers involves assessing their understanding of PHP 7 features, error handling, session management, database connectivity, and security practices. Questions cover key topics like == vs ===, traits, Composer, and RESTful services. Evaluating their knowledge of arrays, OOP principles, and form handling ensures they possess essential skills to contribute effectively to your projects.

1. Explain the differences between ‘include’ and ‘require’ in PHP.

Look for: Knowledge of PHP functions and error handling.

What to Expect: Candidates should understand that both functions include and evaluate specified files. The key difference is that ‘require’ will produce a fatal error (E_COMPILE_ERROR) and stop the script if the file cannot be included, whereas ‘include’ will only produce a warning (E_WARNING) and the script will continue.

2. How do you connect to a MySQL database in PHP?

Look for: Database connection skills and error handling.

What to Expect: Look for knowledge of using ‘mysqli_connect()’ or PDO ($pdo = new PDO(…)). Candidates should mention handling errors and securing database credentials.

3. Describe how to implement prepared statements in PHP.

Look for: Understanding of security practices and SQL injection prevention.

What to Expect: Candidates should demonstrate understanding of using ‘mysqli_prepare()’ or PDO prepared statements to prevent SQL injection attacks, emphasizing binding parameters and executing the statement.

4. What are the main differences between PHP 7 and PHP 8?

Look for: Awareness of language updates and new features.

What to Expect: Expect mention of performance improvements, new features like JIT compilation, and new syntax such as the nullsafe operator and named arguments.

5. How do you handle sessions in PHP?

Look for: Session management and security practices.

What to Expect: Candidates should describe starting a session with ‘session_start()’, setting session variables, and properly ending sessions with ‘session_destroy()’.

6. Explain the MVC pattern and how it applies to PHP frameworks.

Look for: Understanding of architectural patterns and framework usage.

What to Expect: Look for a clear explanation of Model-View-Controller architecture and how it separates concerns. Candidates should mention frameworks like Laravel or Symfony that implement MVC.

7. What are traits in PHP and how do they work?

Look for: Knowledge of OOP principles and code reuse techniques.

What to Expect: Traits are used to include methods in multiple classes. Candidates should explain how traits help in avoiding limitations of single inheritance.

8. How do you implement error handling in PHP?

Look for: Proficiency in managing errors and exceptions.

What to Expect: Expect knowledge of using ‘try-catch’ blocks, custom error handlers with ‘set_error_handler()’, and logging errors using tools like Monolog.

9. What is Composer and how do you use it in PHP development?

Look for: Experience with dependency management tools.

What to Expect: Composer is a dependency manager. Candidates should explain creating a ‘composer.json’ file and using ‘composer install’ and ‘composer update’.

10. Describe the differences between GET and POST methods in PHP.

Look for: Understanding of HTTP methods and data handling.

What to Expect: Candidates should explain that GET appends data to the URL, suitable for non-sensitive data, while POST sends data in the request body, suitable for sensitive data and large data transfers.

11. How do you handle file uploads in PHP?

Look for: Skills in managing file uploads securely.

What to Expect: Candidates should describe using the ‘$_FILES’ superglobal, checking file types and sizes, moving files with ‘move_uploaded_file()’, and handling errors.

12. Explain the concept of namespaces in PHP.

Look for: Understanding of code organization and avoiding name collisions.

What to Expect: Namespaces help in organizing code and avoiding name collisions. Candidates should mention the ‘namespace’ keyword and how to use ‘use’ to import them.

13. How do you implement pagination in a PHP application?

Look for: Skills in managing large datasets and user interfaces.

What to Expect: Look for knowledge of SQL ‘LIMIT’ and ‘OFFSET’ clauses, and creating links to navigate between pages.

14. What are PSR standards in PHP?

Look for: Knowledge of coding standards and best practices.

What to Expect: PSR (PHP Standard Recommendations) are coding standards set by the PHP-FIG. Expect mentions of PSR-1 (Basic Coding Standard), PSR-2 (Coding Style Guide), and PSR-4 (Autoloading Standard).

15. How do you optimize a PHP application for performance?

Look for: Techniques for improving application efficiency.

What to Expect: Candidates should mention caching (using tools like Redis or Memcached), minimizing database queries, using PHP’s built-in opcode cache, and optimizing code.

16. What are closures in PHP?

Look for: Understanding of advanced PHP features and anonymous functions.

What to Expect: Closures are anonymous functions. Candidates should demonstrate understanding by explaining the use of keyword to inherit variables from the parent scope.

17. How do you use arrays in PHP? Provide an example of array functions.

Look for: Proficiency with array operations and functions.

What to Expect: Look for examples like ‘array_map()’, ‘array_filter()’, and ‘array_reduce()’. Candidates should also mention basic operations like adding, removing, and iterating over array elements.

18. Describe how object-oriented programming (OOP) is implemented in PHP.

Look for: Solid understanding of OOP principles and PHP implementation.

What to Expect: Candidates should discuss classes, objects, inheritance, polymorphism, encapsulation, and interfaces. Examples should include defining classes and creating instances.

19. What are PHP magic methods? Give some examples.

Look for: Knowledge of special methods and their uses.

What to Expect: Magic methods start with __, like __construct(), __destruct(), __get(), __set(), and __call(). Candidates should explain their uses and examples.

20. How do you secure a PHP application?

Look for: Security best practices and techniques.

What to Expect: Look for measures like input validation, using prepared statements, sanitizing user input, secure session handling, and proper error reporting.

21. Explain the Singleton design pattern and its use in PHP.

Look for: Understanding of design patterns and their implementation.

What to Expect: The Singleton pattern ensures a class has only one instance and provides a global point of access to it. Candidates should demonstrate how to implement this in PHP.

22. How do you create and handle RESTful APIs in PHP?

Look for: Skills in API development and handling HTTP requests.

WhaLook for: t to Expect: Candidates should describe setting up routes, handling HTTP methods (GET, POST, PUT, DELETE), and using frameworks like Lumen or Slim for building APIs.

23. What are the benefits of using Laravel for PHP development?

Familiarity with PHP frameworks and their advantages.

What to Expect: Expect mentions of Eloquent ORM, Blade templating, middleware, Artisan command-line tool, and Laravel’s modular packaging system.

24. How do you manage database migrations in PHP?

Look for: Experience with schema management and version control.

What to Expect: Candidates should discuss using tools like Laravel’s migration system or Doctrine Migrations for creating, modifying, and managing database schemas.

25. Explain how you would implement authentication in a PHP application.

Look for: Knowledge of authentication mechanisms and security.

What to Expect: Look for knowledge of sessions, cookies, JWT (JSON Web Tokens), and using libraries or frameworks like Laravel Passport for secure authentication.

Stay Informed: Want precision hiring? Check outour tob blog on How to hire a PHP developer?

Code-based PHP developer interview questions to ask applicants

Evaluating a PHP developer’s coding skills can be effectively done through concise code-based interview questions. These questions include tasks such as writing a function to reverse a string, creating a SQL query to fetch the top users by score, and checking if a string is a palindrome. They also involve writing a sorting algorithm like bubble sort and counting vowels in a string. These tasks are designed to be completed in 5-7 minutes each, testing the candidate’s problem-solving abilities, familiarity with basic algorithms, and understanding of PHP syntax and functions. This approach ensures a practical assessment of their coding capabilities.

26. Write a function in PHP to check if a given string is a palindrome.

Look for: Understanding of string manipulation, use of regular expressions, and PHP built-in functions like strtolower() and strrev(). The code should handle edge cases, such as ignoring spaces and punctuation.

function isPalindrome($string) {

    $cleanedString = preg_replace('/[^A-Za-z0-9]/', '', strtolower($string));

    return $cleanedString == strrev($cleanedString);

}

27. Create a PHP function to connect to a MySQL database using PDO.

Look for: Familiarity with PDO for database connections and error handling.

function connectToDatabase($dsn, $username, $password) {
    try {
        $pdo = new PDO($dsn, $username, $password);
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        return $pdo;
    } catch (PDOException $e) {
        echo 'Connection failed: ' . $e->getMessage();
    }
}

28. Write a function in PHP to sort an array of integers in ascending order without using built-in functions.

Look for: Basic understanding of sorting algorithms (bubble sort in this case), ability to implement logic without relying on built-in functions, and proper handling of array indices.

function bubbleSort($arr) {

    $n = count($arr);

    for ($i = 0; $i < $n-1; $i++) {

        for ($j = 0; $j < $n-$i-1; $j++) {

            if ($arr[$j] > $arr[$j+1]) {

                $temp = $arr[$j];

                $arr[$j] = $arr[$j+1];

                $arr[$j+1] = $temp;

            }

        }

    }

    return $arr;

}

29. Write a PHP script to connect to a MySQL database and fetch all records from a table named products.

Look for: Knowledge of database connection in PHP using MySQLi, error handling, and proper usage of SQL queries to fetch data. The code should handle the connection, query execution, and result processing efficiently.

$servername = "localhost";

$username = "username";

$password = "password";

$dbname = "database";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {

    die("Connection failed: " . $conn->connect_error);

}

$sql = "SELECT * FROM products";

$result = $conn->query($sql);

if ($result->num_rows > 0) {

    while($row = $result->fetch_assoc()) {

        echo "id: " . $row["id"]. " - Name: " . $row["name"]. "<br>";

    }

} else {

    echo "0 results";

}

$conn->close();

30. Create a simple PHP class that represents a Book with properties for title, author, and price, and a method to display the book details.

Look for: Understanding of object-oriented programming concepts, including class creation, properties, methods, and constructors. The code should properly instantiate the class and display the book details.

class Book {

    public $title;

    public $author;

    public $price;

    public function __construct($title, $author, $price) {

        $this->title = $title;

        $this->author = $author;

        $this->price = $price;

    }

    public function displayDetails() {

        echo "Title: " . $this->title . "<br>";

        echo "Author: " . $this->author . "<br>";

        echo "Price: $" . $this->price . "<br>";

    }

}

$book = new Book("The Great Gatsby", "F. Scott Fitzgerald", 10.99);

$book->displayDetails();

Interview questions to gauge a candidate’s experience level

31. Can you describe a challenging project you worked on and how you overcame the obstacles you faced?

32. How do you prioritize tasks and manage your time when working on multiple projects?

33. Can you give an example of how you effectively communicated with a non-technical stakeholder about a technical issue?

34. How do you handle tight deadlines and pressure in your work?

35. Describe a time when you had to work as part of a team to complete a project. What role did you play, and how did you ensure the project’s success?

Key takeaways 

Hiring a skilled PHP Developer is crucial due to the high demand and extensive use of PHP in web development, powering approximately 79.2% of websites globally. The importance of PHP in CMS platforms like WordPress, which alone supports 40% of the web, underscores the need for proficient PHP developers​​​ (StackOverflow)​.

Integrating PHP Developer interview questions and code-based assessments throughout the hiring process ensures a thorough evaluation of a candidate’s technical skills, coding proficiency, and problem-solving abilities. Using platforms like Testlify for skills assessments provides objective measures of a candidate’s capabilities, streamlining the hiring process and enhancing the quality of hires.

For a successful hire, look for candidates who demonstrate strong PHP coding skills, experience with database management, and familiarity with web development tools. They should also possess problem-solving skills, a solid understanding of object-oriented programming, and server-side development expertise.

By integrating a mix of technical questions and practical coding tasks, you can effectively gauge a candidate’s readiness to handle real-world development challenges, ensuring they are a good fit for your development team.

Recruit Smarter: Looking to discover talent like a pro? Check out testlify’s PHP Web Developer Test.