What event I can tap into that fires before loading wp-admin page?

The earliest admin related hook I can see is admin_menu, so before that comes (listing only useful core hooks, from later to earlier)

  • auth_redirect
  • update_option
  • wp_loaded
  • init
  • pre_get_posts
  • after_setup_theme
  • get_template_part
  • setup_theme
  • plugins_loaded
  • muplugins_loaded

What are you trying to do, exactly? the complete answer depends on your use case.

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