Drupal 8 Routing YAML example

gistfile1.yml

custom.event.view:
  path: '/admin/structure/custom/{custom}/manage/{custom_event}'
  defaults:
    _content: '\Drupal\custom\Controller\CustomEventController::page'
    _title_callback: '\Drupal\custom\Controller\CustomEventController::pageTitle'
  requirements:
    _permission: 'administer custom'
custom.event.edit:
  path: '/admin/structure/custom/{custom}/manage/{custom_event}/edit'
  defaults:
    _entity_form: 'custom_event.edit'
  requirements:
    _permission: 'administer custom'
custom.event.configure:
  path: '/admin/structure/custom/{custom}/manage/{custom_event}/configure'
  defaults:
    _entity_form: 'custom_event.config'
  requirements:
    _permission: 'administer custom'