Debugging with WP_DEBUG in Wordpress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is WP_DEBUG in WordPress?

WP_DEBUG is a PHP constant in WordPress that enables the display of errors and warnings to help developers find and fix issues in their code.

beginner

How do you enable WP_DEBUG in WordPress?

You enable WP_DEBUG by adding or setting define('WP_DEBUG', true); in the wp-config.php file.

beginner

What happens when WP_DEBUG is set to true?

When WP_DEBUG is true, WordPress shows PHP errors, warnings, and notices on the site, helping developers spot problems early.

intermediate

What is the purpose of WP_DEBUG_LOG?

WP_DEBUG_LOG saves all errors and warnings to a file named debug.log inside the wp-content folder, so you can review them later.

beginner

Why should WP_DEBUG be turned off on live websites?

Because showing errors publicly can reveal sensitive information and confuse visitors, WP_DEBUG should be off on live sites to keep them secure and user-friendly.

Where do you add the line to enable WP_DEBUG?

A In the theme's style.css file

B In the .htaccess file

C In the functions.php file

D In the wp-config.php file

WP_DEBUG is enabled by adding define('WP_DEBUG', true); in the wp-config.php file.

What does setting WP_DEBUG to true do?

A Changes the site theme

B Shows PHP errors and warnings on the site

C Disables all plugins

D Deletes the database

Setting WP_DEBUG to true makes WordPress display PHP errors and warnings to help with debugging.

What file stores error logs when WP_DEBUG_LOG is enabled?

A wp-content/debug.log

B wp-content/error.txt

C wp-config.php

D index.php

When WP_DEBUG_LOG is true, errors are saved in the debug.log file inside the wp-content folder.

Why should WP_DEBUG be off on live sites?

A To enable caching

B To speed up the site theme loading

C To avoid showing sensitive error details to visitors

D To allow plugin updates

Showing errors on live sites can expose sensitive info and confuse users, so WP_DEBUG should be off.

Which of these is NOT a WP_DEBUG related constant?

A WP_DEBUG_THEME

B WP_DEBUG_LOG

C WP_DEBUG

D WP_DEBUG_DISPLAY

WP_DEBUG_THEME is not a valid WordPress debugging constant.

Explain how to enable debugging in WordPress using WP_DEBUG and what you should be careful about.

Think about the file to edit and why showing errors publicly can be risky.

Describe the role of WP_DEBUG_LOG and how it helps developers.

Consider how logging errors to a file is useful compared to showing them on screen.

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