WordPress Bootstrap Hooks

Last updated: February 12, 2026

Hooks fired during WordPress initialization and request handling, in execution order.

Early Bootstrap Hooks

These hooks fire before plugins load. They can only be used by mu-plugins or by pre-defining filters in wp-config.php.

enable_maintenance_mode

Filter whether to enable maintenance mode.

apply_filters( 'enable_maintenance_mode', bool $enable, int $upgrading ): bool

Parameters:

  • $enable – Whether to enable maintenance mode (default true)
  • $upgrading – Timestamp from .maintenance file

Since: 4.6.0

enable_wp_debug_mode_checks

Filter whether to apply debug mode settings.

apply_filters( 'enable_wp_debug_mode_checks', bool $enable ): bool

Default: true

Usage: Define filter in wp-config.php before loading WordPress:

$GLOBALS['wp_filter'] = array(
    'enable_wp_debug_mode_checks' => array(
        10 => array(
            array(
                'accepted_args' => 0,
                'function'      => function() { return false; },
            ),
        ),
    ),
);

Since: 4.6.0

enable_loading_object_cache_dropin

Filter whether to load object-cache.php drop-in.

apply_filters( 'enable_loading_object_cache_dropin', bool $enable ): bool

Default: true

Since: 5.8.0

Plugin Loading Hooks

muplugins_loaded

Action fired after must-use plugins load.

do_action( 'muplugins_loaded' );

When: After mu-plugins are loaded, before regular plugins

Since: 2.8.0

plugins_loaded

Action fired after all plugins load.

do_action( 'plugins_loaded' );

Common Uses:

  • Initialize plugin functionality
  • Register custom post types (though init is preferred)
  • Load plugin textdomains
  • Check for plugin dependencies

Since: 1.5.0

Theme Loading Hooks

setup_theme

Action fired before theme is loaded.

do_action( 'setup_theme' );

When: After plugins loaded, before theme’s functions.php

Common Uses:

  • Register theme support features
  • Initialize theme-related functionality early

Since: 3.0.0

after_setup_theme

Action fired after theme’s functions.php loads.

do_action( 'after_setup_theme' );

Common Uses:

  • add_theme_support()
  • Register nav menus
  • Set content width
  • Load theme textdomain

Example:

add_action( 'after_setup_theme', function() {
    add_theme_support( 'post-thumbnails' );
    add_theme_support( 'title-tag' );
    register_nav_menus( array(
        'primary' => 'Primary Menu',
    ) );
} );

Since: 3.0.0

Initialization Hooks

init

Action fired after WordPress is fully loaded.

do_action( 'init' );

The most important hook. WordPress core, plugins, and themes are all loaded.

Common Uses:

  • Register post types and taxonomies
  • Register shortcodes
  • Initialize sessions
  • Start output buffering
  • Any initialization that requires full WordPress

Example:

add_action( 'init', function() {
    register_post_type( 'book', array(
        'public' => true,
        'label'  => 'Books',
    ) );
} );

Since: 1.0.0

wp_loaded

Action fired after WordPress and all plugins/themes are fully loaded.

do_action( 'wp_loaded' );

When: After init, before request parsing

Common Uses:

  • Buffer flushing
  • Late initialization
  • Actions that must run after all init hooks

Since: 3.0.0

Request Parsing Hooks

do_parse_request

Filter to short-circuit request parsing.

apply_filters( 'do_parse_request', bool $parse, WP $wp, string|array $extra_query_vars ): bool

Return: false to prevent default parsing

Use Case: Custom routing, headless setups

Since: 3.5.0

query_vars

Filter allowed public query variables.

apply_filters( 'query_vars', array $public_query_vars ): array

Example:

add_filter( 'query_vars', function( $vars ) {
    $vars[] = 'my_custom_var';
    return $vars;
} );

Since: 1.5.0

request

Filter the parsed query variables.

apply_filters( 'request', array $query_vars ): array

Example:

add_filter( 'request', function( $query_vars ) {
    if ( isset( $query_vars['my_custom_var'] ) ) {
        $query_vars['post_type'] = 'custom';
    }
    return $query_vars;
} );

Since: 2.1.0

parse_request

Action fired after request variables are parsed.

do_action_ref_array( 'parse_request', array( WP &$wp ) );

Access: $wp->query_vars, $wp->matched_rule, $wp->request

Since: 2.1.0

Headers Hooks

wp_headers

Filter HTTP headers before sending.

apply_filters( 'wp_headers', array $headers, WP $wp ): array

Example:

add_filter( 'wp_headers', function( $headers ) {
    $headers['X-Custom-Header'] = 'value';
    return $headers;
} );

Since: 2.8.0

send_headers

Action fired after headers are sent.

do_action_ref_array( 'send_headers', array( WP &$wp ) );

Since: 2.1.0

404 Handling

pre_handle_404

Filter to short-circuit 404 handling.

apply_filters( 'pre_handle_404', bool $preempt, WP_Query $wp_query ): bool

Return: Non-false to skip default 404 handling

Since: 4.5.0

Main Query Hook

wp

Action fired after WordPress environment is set up.

do_action_ref_array( 'wp', array( WP &$wp ) );

The query is complete. Posts are loaded, conditional tags work.

Common Uses:

  • Redirect logic
  • Access control checks
  • Modify global post data

Example:

add_action( 'wp', function( $wp ) {
    if ( is_singular( 'premium' ) && ! current_user_can( 'read_premium' ) ) {
        wp_redirect( home_url( '/subscribe/' ) );
        exit;
    }
} );

Since: 2.1.0

Template Hooks

template_redirect

Action fired before template loads.

do_action( 'template_redirect' );

Common Uses:

  • Redirects
  • Output buffering
  • Header modifications
  • Access control

Since: 1.5.0

Shutdown Hooks

shutdown

Action fired when PHP shuts down.

do_action( 'shutdown' );

When: Registered via register_shutdown_function()

Common Uses:

  • Cleanup operations
  • Logging
  • Cache operations

Since: 1.2.0

Default Filters (default-filters.php)

This file registers core filter and action callbacks. Key registrations:

Content Filters

// The Content
add_filter( 'the_content', 'do_blocks', 9 );
add_filter( 'the_content', 'wptexturize' );
add_filter( 'the_content', 'convert_smilies', 20 );
add_filter( 'the_content', 'wpautop' );
add_filter( 'the_content', 'shortcode_unautop' );
add_filter( 'the_content', 'do_shortcode', 11 );
add_filter( 'the_content', 'wp_filter_content_tags', 12 );

Title Filters

add_filter( 'the_title', 'wptexturize' );
add_filter( 'the_title', 'convert_chars' );
add_filter( 'the_title', 'trim' );

Excerpt Filters

add_filter( 'the_excerpt', 'wptexturize' );
add_filter( 'the_excerpt', 'convert_smilies' );
add_filter( 'the_excerpt', 'convert_chars' );
add_filter( 'the_excerpt', 'wpautop' );
add_filter( 'get_the_excerpt', 'wp_trim_excerpt', 10, 2 );

Head Actions

add_action( 'wp_head', '_wp_render_title_tag', 1 );
add_action( 'wp_head', 'wp_enqueue_scripts', 1 );
add_action( 'wp_head', 'wp_resource_hints', 2 );
add_action( 'wp_head', 'feed_links', 2 );
add_action( 'wp_head', 'feed_links_extra', 3 );
add_action( 'wp_head', 'wp_robots', 1 );
add_action( 'wp_head', 'wp_print_styles', 8 );
add_action( 'wp_head', 'wp_print_head_scripts', 9 );
add_action( 'wp_head', 'wp_generator' );
add_action( 'wp_head', 'rel_canonical' );
add_action( 'wp_head', 'wp_site_icon', 99 );

Footer Actions

add_action( 'wp_footer', 'wp_print_footer_scripts', 20 );

REST API Actions

add_action( 'init', 'rest_api_init' );
add_action( 'rest_api_init', 'rest_api_default_filters', 10, 1 );
add_action( 'rest_api_init', 'register_initial_settings', 10 );
add_action( 'rest_api_init', 'create_initial_rest_routes', 99 );
add_action( 'parse_request', 'rest_api_loaded' );

Authentication Filters

add_filter( 'authenticate', 'wp_authenticate_username_password', 20, 3 );
add_filter( 'authenticate', 'wp_authenticate_email_password', 20, 3 );
add_filter( 'authenticate', 'wp_authenticate_application_password', 20, 3 );
add_filter( 'authenticate', 'wp_authenticate_spam_check', 99 );
add_filter( 'determine_current_user', 'wp_validate_auth_cookie' );
add_filter( 'determine_current_user', 'wp_validate_logged_in_cookie', 20 );

Cron Actions

add_action( 'init', 'wp_cron' );  // Only if not DOING_CRON

Widget Actions

add_action( 'plugins_loaded', 'wp_maybe_load_widgets', 0 );
add_action( 'init', 'wp_widgets_init', 1 );

Theme Actions

add_action( 'setup_theme', 'create_initial_theme_features', 0 );
add_action( 'after_setup_theme', '_add_default_theme_supports', 1 );

Post Type/Taxonomy Actions

add_action( 'init', 'create_initial_post_types', 0 );
add_action( 'init', 'create_initial_taxonomies', 0 );

Hook Execution Order Summary

  1. enable_maintenance_mode (filter)
  2. enable_wp_debug_mode_checks (filter)
  3. enable_loading_object_cache_dropin (filter)
  4. mu-plugins loaded
  5. muplugins_loaded (action)
  6. plugins loaded
  7. plugins_loaded (action)
  8. setup_theme (action)
  9. theme functions.php loaded
  10. after_setup_theme (action)
  11. init (action)
  12. wp_loaded (action)
  13. do_parse_request (filter)
  14. query_vars (filter)
  15. request (filter)
  16. parse_request (action)
  17. WP_Query executed
  18. pre_handle_404 (filter)
  19. wp_headers (filter)
  20. send_headers (action)
  21. wp (action)
  22. template_redirect (action)
  23. template loaded
  24. shutdown (action)

Protected AJAX Actions

These AJAX actions are protected in recovery mode:

$actions_to_protect = array(
    'edit-theme-plugin-file',
    'heartbeat',
    'install-plugin',
    'install-theme',
    'search-plugins',
    'search-install-plugins',
    'update-plugin',
    'update-theme',
    'activate-plugin',
);

Filter: wp_protected_ajax_actions

Request Type Filters

wp_doing_ajax

apply_filters( 'wp_doing_ajax', bool $is_ajax ): bool

wp_doing_cron

apply_filters( 'wp_doing_cron', bool $is_cron ): bool

wp_using_themes

apply_filters( 'wp_using_themes', bool $use_themes ): bool

Filter/Action Best Practices

Priority Guidelines

  • 0-5: Core functionality, must run first
  • 10: Default priority
  • 11-15: After core filters (e.g., do_shortcode at 11)
  • 20+: Late execution
  • 100+: Final modifications

Common Patterns

// Add custom query var
add_filter( 'query_vars', function( $vars ) {
    $vars[] = 'my_var';
    return $vars;
} );

// Modify request
add_filter( 'request', function( $vars ) {
    if ( isset( $vars['my_var'] ) ) {
        // Modify query based on custom var
    }
    return $vars;
} );

// Late init
add_action( 'wp_loaded', function() {
    // Runs after all init hooks
}, 10 );

// Before template
add_action( 'template_redirect', function() {
    if ( some_condition() ) {
        include get_template_directory() . '/custom-template.php';
        exit;
    }
} );

// Modify headers
add_filter( 'wp_headers', function( $headers ) {
    $headers['X-Frame-Options'] = 'SAMEORIGIN';
    return $headers;
} );

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