admin.php

• URL: /wp-admin/admin.php
• Capability required: No single capability; uses auth_redirect() to require logged-in users, then defers to the current screen’s own capability checks. Raises memory limit if manage_options.
• What it does: Boots the admin, loads menus, sets the current screen, dispatches plugin pages, importers, or core screens, and handles admin_action_* requests.
• Key hooks: admin_init, load-{$page_hook}, load-{$plugin_page}, load-{$pagenow}, admin_action_{$action}, after_db_upgrade, after_mu_upgrade, do_mu_upgrade, force_filtered_html_on_import.

admin-ajax.php

• URL: /wp-admin/admin-ajax.php
• Capability required: Depends on the AJAX action; authenticated actions use wp_ajax_{$action} with handler capability checks. Public actions use wp_ajax_nopriv_{$action}.
• What it does: Ajax dispatcher for admin and front-end requests. Loads admin bootstrap and runs the registered AJAX action callback.
• Key hooks: admin_init, wp_ajax_{$action}, wp_ajax_nopriv_{$action}.

admin-post.php

• URL: /wp-admin/admin-post.php
• Capability required: Depends on handler; authenticated posts use admin_post_{$action} (user must be logged in). Public posts use admin_post_nopriv_{$action}.
• What it does: Handles generic form posts into the admin without page rendering. Dispatches by the action request parameter.
• Key hooks: admin_init, admin_post, admin_post_{$action}, admin_post_nopriv, admin_post_nopriv_{$action}.

admin-header.php

• URL: Included by admin screens (not typically requested directly).
• Capability required: No direct checks; depends on the calling screen.
• What it does: Renders the admin header (title, menus, notices), enqueues scripts/styles, and outputs the opening admin markup.
• Key hooks: admin_enqueue_scripts, admin_head, admin_head-{$hook_suffix}, admin_print_scripts, admin_print_scripts-{$hook_suffix}, admin_print_styles, admin_print_styles-{$hook_suffix}, admin_notices, all_admin_notices, network_admin_notices, user_admin_notices, in_admin_header, admin_body_class, admin_title.

admin-footer.php

• URL: Included by admin screens (not typically requested directly).
• Capability required: No direct checks; depends on the calling screen.
• What it does: Renders admin footer markup and prints footer scripts.
• Key hooks: admin_footer, admin_footer-{$hook_suffix}, admin_print_footer_scripts, admin_print_footer_scripts-{$hook_suffix}, admin_footer_text, update_footer, in_admin_footer.