Debugging with WP_DEBUG in Wordpress - Mini Project: Build & Apply

Debugging with WP_DEBUG in WordPress

📖 Scenario: You are building a WordPress site and want to find and fix errors easily. WordPress has a special tool called WP_DEBUG that helps show problems in your code.This project will guide you step-by-step to enable and use WP_DEBUG to see error messages and warnings on your site.

🎯 Goal: Enable WordPress debugging by setting WP_DEBUG to true in the wp-config.php file, configure error logging, and display errors on the site for easier troubleshooting.

📋 What You'll Learn

Edit the wp-config.php file

Create a variable to enable debugging

Configure error logging to a file

Enable error display on the site

💡 Why This Matters

🌍 Real World

Developers use WP_DEBUG to find mistakes in their WordPress themes and plugins quickly by seeing error messages.

💼 Career

Knowing how to enable and use WP_DEBUG is essential for WordPress developers and site maintainers to troubleshoot and fix issues efficiently.

1

Enable WP_DEBUG in wp-config.php

Open the wp-config.php file and add the line define('WP_DEBUG', true); before the line that says /* That's all, stop editing! Happy blogging. */ to turn on debugging.

Wordpress

<?php
// Some initial WordPress config code

define('WP_DEBUG', true);
/* That's all, stop editing! Happy blogging. */
# Your code here

Hint

Use define('WP_DEBUG', true); exactly to enable debugging.

2

Enable error logging to a file

Add the line define('WP_DEBUG_LOG', true); below define('WP_DEBUG', true); in wp-config.php to save errors to a debug log file.

Wordpress

<?php
// Some initial WordPress config code

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
/* That's all, stop editing! Happy blogging. */
# Your code here

Hint

Use define('WP_DEBUG_LOG', true); to log errors to wp-content/debug.log.

3

Enable error display on the site

Add the line define('WP_DEBUG_DISPLAY', true); below define('WP_DEBUG_LOG', true); in wp-config.php to show errors directly on your website pages.

Wordpress

<?php
// Some initial WordPress config code

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', true);
/* That's all, stop editing! Happy blogging. */
# Your code here

Hint

Use define('WP_DEBUG_DISPLAY', true); to see errors on the site pages.

4

Complete wp-config.php with debugging setup

Ensure the wp-config.php file contains these three lines exactly before the stop editing comment:
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', true);

Wordpress

<?php
// Some initial WordPress config code

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', true);
/* That's all, stop editing! Happy blogging. */
# Your code here

Hint

Check all three define lines are present exactly before the stop editing comment.

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