metatag-8.x-1.x-dev/metatag_routes/metatag_routes.routing.yml

metatag_routes.create:
  path: '/admin/config/search/metatag/custom/create'
  defaults:
    _form: '\Drupal\metatag_routes\Form\MetatagCustomCreateForm'
    _title: 'Add custom metatag'
  requirements:
    _permission: 'administer meta tags'
  options:
    _admin_route: TRUE