Purpose

Core bootstrap that initializes WordPress: loads core libraries, sets constants, configures DB/cache, loads plugins and themes, and fires the key lifecycle hooks (init, wp_loaded).

Flow

• Defines WPINC and loads core version/compat/load files.
• Checks server requirements and registers fatal error handler.
• Initializes constants, time zone, server vars, maintenance mode, timers, and debug mode.
• Loads early core libraries and sets up database access (require_wp_db, wp_set_wpdb_vars).
• Starts object cache and default filters.
• Loads multisite stack when enabled.
• Loads MU plugins, network plugins, then active plugins.
• Loads pluggable functions and sets encoding/magic quotes.
• Instantiates globals (WP_Query, WP_Rewrite, WP, WP_Roles, etc.).
• Loads themes’ functions.php, then fires theme hooks.
• Initializes current user, runs init, checks multisite site status, and fires wp_loaded.

Key functions called

• wp_initial_constants()
• wp_register_fatal_error_handler()
• wp_fix_server_vars()
• wp_maintenance()
• timer_start()
• wp_debug_mode()
• require_wp_db()
• wp_set_wpdb_vars()
• wp_start_object_cache()
• wp_plugin_directory_constants()
• create_initial_taxonomies() / create_initial_post_types()
• wp_not_installed()
• wp_templating_constants() / wp_set_template_globals()
• load_default_textdomain()
• $GLOBALS['wp']->init()

Hooks fired

• Filters:
  • enable_loading_advanced_cache_dropin
• Actions:
  • mu_plugin_loaded
  • network_plugin_loaded
  • muplugins_loaded
  • plugin_loaded
  • plugins_loaded
  • sanitize_comment_cookies
  • setup_theme
  • after_setup_theme
  • init
  • wp_loaded