How to enable debug mode in PrestaShop?

How to enable displaying error messages or debugging in Prestashop?

PrestaShop's default settings prevent the customer to see any server error message or any debugging code. You, on the other hand, need this information in order to correct any potential mistake in your code.

For PS1.5-1.6: Open the «/config/defines.inc.php» file, and edit it to set «_PS_MODE_DEV_» to «true»:

define('_PS_MODE_DEV_', true);

For PS1.2-1.4: Open the «/config/config.inc.php» file, and edit it to set «display_errors» to «on»:

@ini_set('display_errors', 'on');

For PS1.4 (additional): you may to enable debug functions: p() and d() by setting «_PS_MODE_DEV_» to «true» in the «/config/defines.inc.php» file.

See also «How to enable a debug mode for a programmer when a shop on the production??».