Drupal 8 is admin path
To check the path of the current page:
<?php
$is_admin = \Drupal::service('router.admin_context')->isAdminRoute();to check an arbitrary path, you need to create a Request object and obtain its matching Route:
<?php
use Symfony\Component\HttpFoundation\Request;use Symfony\Cmf\Component\Routing\RouteObjectInterface;
$path ='/node/1'; $request =Request::create($path);
$route_match = \Drupal::service('router.no_access_checks')->matchRequest($request);
$route = $route_match[RouteObjectInterface::ROUTE_OBJECT];
$is_admin = \Drupal::service('router.admin_context')->isAdminRoute($route);