Using WordPress ‘domain_exists’ PHP filter

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The domain_exists WordPress PHP filter checks if a site name is already taken. The name can be a site’s subdomain or subdirectory path, depending on the network settings.

Usage

add_filter('domain_exists', 'your_custom_function', 10, 4);
function your_custom_function($result, $domain, $path, $network_id) {
    // your custom code here

    return $result;
}

Parameters

  • $result: (int|null) The site ID if the site name exists, null otherwise.
  • $domain: (string) Domain to be checked.
  • $path: (string) Path to be checked.
  • $network_id: (int) Network ID. Only relevant on multi-network installations.

More information

See WordPress Developer Resources: domain_exists

Examples

Check for Custom Domain Conflicts

Prevent site creation if the domain contains “example.com”

add_filter('domain_exists', 'prevent_example_domain', 10, 4);
function prevent_example_domain($result, $domain, $path, $network_id) {
    if (strpos($domain, 'example.com') !== false) {
        return true;
    }
    return $result;
}

Limit Subdirectory Depth

Disallow site creation if the subdirectory depth is more than 2 levels

add_filter('domain_exists', 'limit_subdirectory_depth', 10, 4);
function limit_subdirectory_depth($result, $domain, $path, $network_id) {
    if (substr_count($path, '/') > 2) {
        return true;
    }
    return $result;
}

Block Certain Domain Names

Disallow site creation if the domain name matches a list of blocked domains

add_filter('domain_exists', 'block_domains', 10, 4);
function block_domains($result, $domain, $path, $network_id) {
    $blocked_domains = array('blocked.com', 'forbidden.net');
    if (in_array($domain, $blocked_domains)) {
        return true;
    }
    return $result;
}

Allow Specific Domain Only

Allow site creation only if the domain name contains a specific keyword

add_filter('domain_exists', 'allow_specific_domain', 10, 4);
function allow_specific_domain($result, $domain, $path, $network_id) {
    if (strpos($domain, 'allowed') === false) {
        return true;
    }
    return $result;
}

Custom Validation Based on Network ID

Validate the domain and path based on the network ID

add_filter('domain_exists', 'custom_validation_based_on_network', 10, 4);
function custom_validation_based_on_network($result, $domain, $path, $network_id) {
    if ($network_id == 1 && strpos($domain, 'network1') === false) {
        return true;
    }
    if ($network_id == 2 && strpos($path, 'network2') === false) {
        return true;
    }
    return $result;
}