Debug mode shows PHP errors, which helps track down problems.
Edit wp-config.php and find define( 'WP_DEBUG', false );. Replace it with:
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );
This records errors in wp-content/debug.log without showing them to visitors. To see errors on screen instead, set WP_DEBUG_DISPLAY to true, but only briefly on a live site.
When finished
Set WP_DEBUG back to false and delete debug.log, which can reveal information about your site and grow very large.
