WordPress wp-config.php Constants: What WP_DEBUG and Memory Limits Actually Control

WordPress uses a PHP file called wp-config.php to store configuration constants that must be loaded before the application boots, making them separate from dashboard settings stored in the database. Three debug-related constants — WP_DEBUG, WP_DEBUG_DISPLAY, and WP_DEBUG_LOG — control whether PHP errors are detected, shown to visitors, or written silently to a log file. A common production setup enables WP_DEBUG and WP_DEBUG_LOG while disabling WP_DEBUG_DISPLAY, so errors are recorded without being exposed to site visitors. WordPress also defines two memory constants, WP_MEMORY_LIMIT for front-end requests and WP_MAX_MEMORY_LIMIT for heavier admin tasks, layered on top of PHP's own server-wide memory ceiling. Exceeding either memory limit causes PHP to terminate the request immediately, making correct configuration of these constants critical for site stability and error diagnosis.