Here’s how easy it use to use any of WordPress default functionality from any PHP file outside of the WordPress installation directory.
One step
Add this to the beginning of your external (non-WP) PHP file(s):
<?php require(‘../wp-install-directory/wp-load.php’); ?>
Once the wp-load.php file is included properly, all native WordPress functions are yours for the using. Enjoy!
Content retrieved from: https://wp-mix.com/wp-functions-outside-wordpress/.