Add tab for custom entity type on content page

Question

I made a custom entity type and I'd like it added to the tabs on the content page seen below.

My custom_entity.links.menu.yml Looks like this

entity.custom_entity.collection:
  title: 'Custom Entities'
  route_name: 'entity.custom_entity.collection'
  description: 'List Custom Entities'
  parent: system.admin_content
entity.custom_entity.add_form:
  title: 'Add Custom Entity'
  route_name: 'entity.custom_entity.collection'
  description: 'Add custom entity'
  parent: entity.custom_entity.collection
custom_entity.admin.structure.settings:
  title: 'Custom Entity Settings'
  description: 'Configure Custom Entity'
  route_name: 'custom_entity.settings'
  parent: system.admin_structure

And it does display the custom entity pages in the admin menu but it does not appear amongst the tabs on the content page. Is there a separate yml file that governs that?

Answer 1

Those tabs called "local tasks." See Providing module-defined local tasks on d.o.

In the simplest case you can define your local tasks in a yaml file:

# example.links.task.yml

example.admin: # The first plugin ID
  route_name: example.admin  
  title: 'Settings'
  base_route: example.admin

example.admin_3rd_party: # The second plugin ID
  route_name: example.admin_3rd_party
  title: 'Third party services'
  base_route: example.admin
  weight: 100

But, it's also possible to define dynamic local tasks.

Per @Matt in the comments, if you want to place this as a tab on the /admin/content page, use base_route: system.admin_content.