Does WordPress work without a theme?

Does WordPress work without a theme? If so, then how does it work? Please explain in brief.

If WordPress is displaying content without a theme, what controls the output?

I think there’s a song for that:

“Imagine there’s no theme. It’s easy if you try. No hell below us.
Above us only sky …” 😉

So in that imaginary dream:

• you can still fetch the RSS feeds from your site:

  example.com/feed/
  

• you can still login to your backend:

  example.com/wp-login.php
  

• you can still access the backend and work there (almost) as usual:

  example.com/wp-admin/
  

• scheduling posts will not work so you will get the Missed schedule message.

• wp-cron will not be reliable.

• you can still access /wp-admin/admin-ajax.php

• you can use the template_redirect and tempate_include hooks to control the output. Try for example this tiny plugin:

  <?php
  /** Plugin Name: No-Theme-Day **/
  add_action( 'template_redirect', 
      function()
      { 
          wp_die( __( "Jibby! It's the No-Theme-Day today!" ) ); 
      } 
  );
  

• …

ps: Forgive my Friday answer – “But I’m not the only one” 😉