How to Debug PHP Code: Step-by-Step Guide for Beginners

Debugging is an essential skill every PHP developer must master. Whether you’re fixing a white screen of death, resolving a syntax error, or tracing incorrect output, learning how to debug PHP code effectively can save time, reduce frustration, and improve code quality.

In this guide, we’ll show you through multiple debugging techniques — from basic error reporting to advanced tools like Xdebug and PHP IDE integrations.

What Is Debugging in PHP?

Debugging in PHP refers to the process of identifying, analyzing, and resolving bugs, errors, or unexpected behaviors in your code. These errors could be:

Syntax errors (e.g., missing semicolons)
Runtime errors (e.g., calling an undefined function)
Logical errors (e.g., incorrect output due to wrong conditions)

Step-by-Step: How to Debug PHP Code

Here’s a list of proven debugging techniques, starting from the most basic and moving to more advanced methods:

Step 1: Enable PHP Error Reporting

By default, many servers hide errors. To view them:

ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

This tells PHP to show all warnings, notices, and fatal errors in the browser — critical during development.

💡 Pro Tip: Never enable display_errors in production. Instead, log them to a file.

Step 2: Check PHP Error Logs

When errors aren’t visible, especially in production, logs are your best friend.

Common log file paths:

Linux (Apache): /var/log/apache2/error.log
Linux (Nginx + PHP-FPM): /var/log/php7.x-fpm.log
Windows (XAMPP/WAMP): xampp/php/logs/php_error_log

You can also log custom messages:

error_log("Debug: Variable = " . print_r($variable, true));

Step 3: Use `var_dump()`, `print_r()`, and `echo()`

Use these to inspect data inside your variables:

var_dump($user);
print_r($userArray);
echo $userName;

These are the quickest ways to check what values your code is working with.

Step 4: Use `die()` or `exit()` for Quick Checks

You can halt script execution mid-way to pinpoint the bug:

echo "Before the error";
var_dump($data);
die("Stopping here");

This is helpful to isolate the part of code causing the issue.

Step 5: Install and Configure Xdebug (Advanced)

Xdebug is a powerful PHP extension that gives you in-depth debugging features.

Xdebug Features:

Line-by-line code execution
Breakpoints
Stack traces
Variable watches
Performance profiling

Basic setup:

Check your PHP version: nginxCopyEditphp -v
Visit https://xdebug.org to generate install instructions.
Add this to your php.ini: iniCopyEditzend_extension="xdebug.so" ; or xdebug.dll on Windows xdebug.mode=debug xdebug.start_with_request=yes

Then restart your web server.

Step 6: Use PHP Debugging in IDEs (VS Code, PhpStorm, etc.)

Using an IDE with Xdebug enables professional-grade debugging.

Example: Debugging in Visual Studio Code

Install PHP Debug extension by Felix Becker
Add a launch.json config file
Start a debugging session
Set breakpoints, step over code, and watch variables

Popular IDEs for PHP debugging:

VS Code (Free)
PhpStorm (Paid but powerful)
NetBeans

Step 7: Handle Exceptions with `try-catch`

Use try-catch to gracefully handle exceptions:

try {
    riskyFunction();
} catch (Exception $e) {
    error_log($e->getMessage());
    echo "Something went wrong!";
}

This is especially useful for database errors, file handling, or API requests.

Step 8: Use PHPUnit for Automated Debugging

PHPUnit is a testing framework that allows you to write test cases to verify your code behaves as expected.

Example:

class MathTest extends PHPUnit\Framework\TestCase {
    public function testAddition() {
        $this->assertEquals(4, 2 + 2);
    }
}

This helps catch bugs early during development.

Best Practices for PHP Debugging

Always debug in a local or staging environment
Never display detailed errors in production
Use logging to collect error info silently
Write tests using PHPUnit or PestPHP
Use version control to track bug history

Common PHP Debugging Questions (FAQs)

Q1. How do I turn on PHP error reporting?
A: Add error_reporting(E_ALL); ini_set('display_errors', 1); at the top of your script.

Q2. What is the best PHP debugger?
A: Xdebug combined with an IDE like PhpStorm or VS Code is the best choice.

Q3. Can I debug PHP using Chrome or a browser?
A: You can’t directly debug PHP in a browser DevTools like JavaScript, but browser tools can help you inspect AJAX requests and responses.

Q4. Is var_dump() good enough?
A: For small projects or quick checks, yes. For large apps, use Xdebug and proper logging.

Final Thoughts

Debugging is a critical skill for every PHP developer. Whether you’re using simple echo statements or advanced tools like Xdebug, the key is to trace the issue logically, isolate the bug, and fix it methodically.

By following the steps above, you’ll become faster and more confident at finding and fixing errors in your PHP code.