Site constants

WP Cloud defines PHP constants that identify the platform, site, and host client. Plugins and themes can use them when behavior should apply only to WP Cloud or to sites belonging to a particular host client.

Constant	Value
IS_ATOMIC	Defined as true on WP Cloud infrastructure.
ATOMIC_SITE_ID	The site’s persistent Atomic Site ID.
ATOMIC_CLIENT_ID	The ID of the WP Cloud host client that owns the site.

Check that a constant exists before using it. For example, the following code runs only on WP Cloud sites owned by client ID 2:

if (
    defined( 'IS_ATOMIC' )
    && IS_ATOMIC
    && defined( 'ATOMIC_CLIENT_ID' )
    && '2' === ATOMIC_CLIENT_ID
) {
    // Run WP Cloud client-specific code.
}Code language: JavaScript (javascript)Copy

Use Persistent Data for values that vary by site and must be supplied by the host client. Do not treat Persistent Data as the primary source of truth.