Why Debugging with WP_DEBUG in Wordpress? - Purpose & Use Cases

The Big Idea

Discover how a simple switch can save you hours of frustrating guesswork in WordPress!

The Scenario

Imagine trying to find a tiny mistake in your WordPress site's code without any clues. You refresh the page, but nothing tells you what went wrong or where.

The Problem

Without debugging tools, errors stay hidden. You waste time guessing, checking files one by one, and hoping you spot the problem. This is slow, frustrating, and can break your site without warning.

The Solution

WP_DEBUG turns on helpful error messages and warnings right on your site. It shows exactly what and where the problem is, so you can fix issues quickly and confidently.

Before vs After

✗ Before

<?php
// No error messages shown
// You just see a blank page or broken layout
?>

✓ After

<?php
define('WP_DEBUG', true);
// Now errors and warnings appear on the page
?>

What It Enables

WP_DEBUG makes finding and fixing WordPress code problems fast and clear, saving you hours of guesswork.

Real Life Example

When a plugin causes your site to crash, WP_DEBUG shows the exact file and line causing the error, so you can fix or disable it immediately.

Key Takeaways

Manually finding WordPress errors is slow and frustrating.

WP_DEBUG reveals errors and warnings clearly on your site.

This helps you fix problems faster and keep your site running smoothly.

Practice

1. What is the main purpose of enabling WP_DEBUG in WordPress?

easy

A. To speed up the website loading time

B. To display and log PHP errors and warnings for debugging

C. To disable all plugins temporarily

D. To change the website theme automatically

Solution

1. Step 1: Understand WP_DEBUG role

   WP_DEBUG is a constant in WordPress that helps developers see PHP errors and warnings.

2. Step 2: Identify its main use

   It is used to display and log errors to help fix issues during development.

3. Final Answer:

   To display and log PHP errors and warnings for debugging -> Option B

4. Quick Check:

   WP_DEBUG shows errors = B [OK]

Hint: WP_DEBUG shows errors to help fix bugs [OK]

Common Mistakes:

• Thinking WP_DEBUG speeds up the site
• Confusing WP_DEBUG with plugin management
• Assuming WP_DEBUG changes themes

2. Which line correctly enables debugging in the wp-config.php file?

easy

A. define('WP_DEBUG', false);

B. define(WP_DEBUG, true);

C. WP_DEBUG = true;

D. define('WP_DEBUG', true);

Solution

1. Step 1: Check correct syntax for defining constants in PHP

   Constants are defined using define('NAME', value); with quotes around the name.

2. Step 2: Identify correct value to enable debugging

   Setting WP_DEBUG to true enables debugging.

3. Final Answer:

   define('WP_DEBUG', true); -> Option D

4. Quick Check:

   Correct PHP constant syntax with true = C [OK]

Hint: Use define('WP_DEBUG', true); with quotes and semicolon [OK]

Common Mistakes:

• Missing quotes around WP_DEBUG
• Using assignment (=) instead of define()
• Setting WP_DEBUG to false to enable debugging

3. Given this code in wp-config.php:

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

What happens when a PHP error occurs?

medium

A. Error is logged to debug.log but not shown on the website

B. Error is neither shown nor logged

C. Error is shown on the website and logged to debug.log

D. Error is shown on the website but not logged

Solution

1. Step 1: Analyze WP_DEBUG_DISPLAY setting

   WP_DEBUG_DISPLAY is set to false, so errors are not shown on the website.

2. Step 2: Analyze WP_DEBUG_LOG setting

   WP_DEBUG_LOG is true, so errors are logged to the debug.log file.

3. Final Answer:

   Error is logged to debug.log but not shown on the website -> Option A

4. Quick Check:

   Display false + Log true = A [OK]

Hint: Display false hides errors; log true saves them [OK]

Common Mistakes:

• Assuming errors show on site when WP_DEBUG_DISPLAY is false
• Thinking errors are not logged if not displayed
• Confusing WP_DEBUG_LOG with WP_DEBUG_DISPLAY

4. You enabled WP_DEBUG but no errors appear on your site or in the log file. What is the most likely cause?

medium

A. You forgot to set WP_DEBUG_LOG to true

B. You set WP_DEBUG_DISPLAY to true

C. You set WP_DEBUG to false

D. You did not save the wp-config.php file

Solution

1. Step 1: Check WP_DEBUG status

   WP_DEBUG is enabled, so errors should appear or be logged.

2. Step 2: Check if errors are logged

   If WP_DEBUG_LOG is not true, errors won't be saved to the log file.

3. Final Answer:

   You forgot to set WP_DEBUG_LOG to true -> Option A

4. Quick Check:

   Logging off means no error logs = A [OK]

Hint: Enable WP_DEBUG_LOG to save errors to file [OK]

Common Mistakes:

• Thinking WP_DEBUG_DISPLAY controls logging
• Assuming WP_DEBUG false but errors show
• Not saving wp-config.php after changes

5. You want to debug a plugin error but avoid showing errors to visitors. Which settings in wp-config.php should you use?

hard

A. define('WP_DEBUG', false);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

B. define('WP_DEBUG', false);
define('WP_DEBUG_LOG', false);
define('WP_DEBUG_DISPLAY', true);

C. define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

D. define('WP_DEBUG', true);
define('WP_DEBUG_LOG', false);
define('WP_DEBUG_DISPLAY', true);

Solution

1. Step 1: Enable debugging without showing errors

   Set WP_DEBUG to true to enable debugging and WP_DEBUG_DISPLAY to false to hide errors from visitors.

2. Step 2: Enable logging to capture errors

   Set WP_DEBUG_LOG to true to save errors to the debug.log file for review.

3. Final Answer:

   define('WP_DEBUG', true); define('WP_DEBUG_LOG', true); define('WP_DEBUG_DISPLAY', false); -> Option C

4. Quick Check:

   Debug on + Log on + Display off = D [OK]

Hint: Show no errors but log them with WP_DEBUG_DISPLAY false [OK]

Common Mistakes:

• Turning off WP_DEBUG disables all error reporting
• Showing errors to visitors by setting WP_DEBUG_DISPLAY true
• Not enabling WP_DEBUG_LOG so errors are lost