WordPress Loading Functions

Last updated: February 12, 2026

Functions defined in wp-includes/load.php that handle WordPress initialization.

Server Environment Functions

wp_get_server_protocol()

Returns the HTTP protocol sent by the server.

function wp_get_server_protocol(): string

Returns: HTTP protocol string (HTTP/1.0, HTTP/1.1, HTTP/2, HTTP/3)

Since: 4.4.0

wp_fix_server_vars()

Fixes $_SERVER variables for various hosting setups.

function wp_fix_server_vars(): void

Purpose:

Normalizes REQUEST_URI for IIS
Handles ISAPI_Rewrite and IIS Mod-Rewrite
Fixes SCRIPT_FILENAME for PHP CGI
Populates empty PHP_SELF
Calls wp_populate_basic_auth_from_authorization_header()

Since: 3.0.0

wp_populate_basic_auth_from_authorization_header()

Extracts Basic Auth credentials from the Authorization header.

function wp_populate_basic_auth_from_authorization_header(): void

Purpose: CGI/FastCGI servers often don’t pass PHP_AUTH_USER and PHP_AUTH_PW. This function extracts them from HTTP_AUTHORIZATION header.

Since: 5.6.0

Requirements Checking

wp_check_php_mysql_versions()

Validates server meets minimum requirements.

function wp_check_php_mysql_versions(): void

Checks:

PHP version >= $required_php_version
Required PHP extensions (json, hash)
MySQLi extension (unless db.php drop-in exists)

Dies: With error message if requirements not met.

Since: 3.0.0

Environment Functions

wp_get_environment_type()

Returns the current environment type.

function wp_get_environment_type(): string

Returns: One of: local, development, staging, production

Configuration:

// In wp-config.php
define( 'WP_ENVIRONMENT_TYPE', 'development' );

// Or environment variable
putenv( 'WP_ENVIRONMENT_TYPE=development' );

Since: 5.5.0

wp_get_development_mode()

Returns the current development mode.

function wp_get_development_mode(): string

Returns: One of: core, plugin, theme, all, or empty string

Configuration:

define( 'WP_DEVELOPMENT_MODE', 'theme' );

Since: 6.3.0

wp_is_development_mode()

Checks if a specific development mode is active.

function wp_is_development_mode( string $mode ): bool

Parameters:

$mode – Mode to check: core, plugin, theme, or all

Since: 6.3.0

Maintenance Mode

wp_maintenance()

Displays maintenance message and dies if maintenance mode is active.

function wp_maintenance(): void

Behavior:

Checks wp_is_maintenance_mode()
Loads wp-content/maintenance.php drop-in if exists
Otherwise shows default message with 503 status

Since: 3.0.0

wp_is_maintenance_mode()

Checks if maintenance mode is enabled.

function wp_is_maintenance_mode(): bool

Logic:

Checks for .maintenance file in ABSPATH
File must contain $upgrading timestamp
Timestamp must be < 10 minutes old
Returns false during installation

Filter: enable_maintenance_mode

Since: 5.5.0

Timer Functions

timer_float()

Gets elapsed time since PHP script start.

function timer_float(): float

Returns: Seconds since $_SERVER['REQUEST_TIME_FLOAT']

Since: 5.8.0

timer_start()

Starts the WordPress page timer.

function timer_start(): bool

Sets: $timestart global

Since: 0.71

timer_stop()

Returns time elapsed since timer_start().

function timer_stop( int|bool $display = 0, int $precision = 3 ): string

Parameters:

$display – Echo result (1/true) or return (0/false)
$precision – Decimal places

Since: 0.71

Debug Mode

wp_debug_mode()

Configures PHP error reporting based on WP_DEBUG settings.

function wp_debug_mode(): void

Constants Used:

WP_DEBUG – Enable debug mode
WP_DEBUG_DISPLAY – Display errors (default: true)
WP_DEBUG_LOG – Log errors to debug.log or custom path

Behavior:

WP_DEBUG=true: error_reporting(E_ALL)
WP_DEBUG=false: Reports only core/compile/parse errors
Disables display for XMLRPC, REST, AJAX, JSON requests

Filter: enable_wp_debug_mode_checks

Since: 3.0.0

Language Directory

wp_set_lang_dir()

Sets the WP_LANG_DIR constant.

function wp_set_lang_dir(): void

Priority:

Custom WP_LANG_DIR if already defined
WP_CONTENT_DIR/languages if exists
ABSPATH/WPINC/languages fallback

Since: 3.0.0

Database Functions

require_wp_db()

Loads wpdb class and creates $wpdb instance.

function require_wp_db(): void

Process:

Includes class-wpdb.php
Includes wp-content/db.php drop-in if exists
Creates new wpdb() with credentials from constants

Since: 2.5.0

wp_set_wpdb_vars()

Configures database table prefix and field types.

function wp_set_wpdb_vars(): void

Sets:

$wpdb->field_types – Format specifiers for columns
Table prefix via $wpdb->set_prefix()

Dies: If table prefix is invalid

Since: 3.0.0

Object Cache

wp_using_ext_object_cache()

Gets/sets whether external object cache is in use.

function wp_using_ext_object_cache( ?bool $using = null ): bool

Parameters:

$using – Set value, or null to just get current value

Since: 3.7.0

wp_start_object_cache()

Initializes the object cache system.

function wp_start_object_cache(): void

Process:

Loads object-cache.php drop-in if exists
Otherwise loads built-in cache (cache.php)
Calls wp_cache_init()
Registers global cache groups (for multisite)
Registers non-persistent groups

Filter: enable_loading_object_cache_dropin

Since: 3.0.0

Installation Check

wp_not_installed()

Redirects to installer if WordPress is not installed.

function wp_not_installed(): void

Behavior:

Returns if is_blog_installed() or wp_installing()
On multisite: dies with error
Otherwise: redirects to /wp-admin/install.php

Since: 3.0.0

Plugin Loading

wp_get_mu_plugins()

Gets array of must-use plugin files.

function wp_get_mu_plugins(): array

Returns: Array of absolute paths to PHP files in WPMU_PLUGIN_DIR

Since: 3.0.0

wp_get_active_and_valid_plugins()

Gets active plugin files.

function wp_get_active_and_valid_plugins(): array

Process:

Reads active_plugins option
Validates each plugin file exists
Excludes network plugins (if multisite)
Skips paused plugins in recovery mode

Since: 3.0.0

wp_skip_paused_plugins()

Removes paused plugins from array.

function wp_skip_paused_plugins( array $plugins ): array

Purpose: Recovery mode skips plugins that caused fatal errors.

Since: 5.2.0

Theme Loading

wp_get_active_and_valid_themes()

Gets active theme directories.

function wp_get_active_and_valid_themes(): array

Returns: Array with child theme path (if applicable) and parent theme path

Since: 5.1.0

wp_skip_paused_themes()

Removes paused themes from array.

function wp_skip_paused_themes( array $themes ): array

Since: 5.2.0

Recovery Mode

wp_is_recovery_mode()

Checks if recovery mode is active.

function wp_is_recovery_mode(): bool

Since: 5.2.0

is_protected_endpoint()

Checks if current endpoint should be protected against WSODs.

function is_protected_endpoint(): bool

Protected:

wp-login.php
Admin backend (non-AJAX)
Protected AJAX actions

Filter: is_protected_endpoint

Since: 5.2.0

is_protected_ajax_action()

Checks if current AJAX action should be protected.

function is_protected_ajax_action(): bool

Protected Actions:

edit-theme-plugin-file
heartbeat
install-plugin
install-theme
update-plugin
update-theme
activate-plugin

Filter: wp_protected_ajax_actions

Since: 5.2.0

Encoding

wp_set_internal_encoding()

Sets PHP internal encoding to UTF-8.

function wp_set_internal_encoding(): void

Since: 3.0.0

wp_magic_quotes()

Adds magic quotes to superglobals.

function wp_magic_quotes(): void

Process:

Escapes $_GET, $_POST, $_COOKIE, $_SERVER
Rebuilds $_REQUEST as $_GET + $_POST

Since: 3.0.0

Shutdown

shutdown_action_hook()

Fires shutdown action and closes cache.

function shutdown_action_hook(): void

Fires: shutdown action

Since: 1.2.0

Context Detection

is_login()

Checks if on login screen.

function is_login(): bool

Since: 6.1.0

is_admin()

Checks if in admin area.

function is_admin(): bool

Since: 1.5.1

is_blog_admin()

Checks if in site admin (not network admin).

function is_blog_admin(): bool

Since: 3.1.0

is_network_admin()

Checks if in network admin.

function is_network_admin(): bool

Since: 3.1.0

is_user_admin()

Checks if in user admin.

function is_user_admin(): bool

Since: 3.1.0

is_multisite()

Checks if Multisite is enabled.

function is_multisite(): bool

Since: 3.0.0

Utility Functions

absint()

Converts value to non-negative integer.

function absint( mixed $maybeint ): int

Since: 2.5.0

get_current_blog_id()

Returns current site ID.

function get_current_blog_id(): int

Since: 3.1.0

get_current_network_id()

Returns current network ID.

function get_current_network_id(): int

Since: 4.6.0

wp_installing()

Checks/sets installation mode.

function wp_installing( ?bool $is_installing = null ): bool

Since: 4.4.0

is_ssl()

Determines if SSL is being used.

function is_ssl(): bool

Checks:

$_SERVER['HTTPS'] is ‘on’ or ‘1’
$_SERVER['SERVER_PORT'] is 443

Since: 2.6.0

Request Detection

wp_doing_ajax()

Checks if current request is WordPress AJAX.

function wp_doing_ajax(): bool

Filter: wp_doing_ajax

Since: 4.7.0

wp_doing_cron()

Checks if current request is WP-Cron.

function wp_doing_cron(): bool

Filter: wp_doing_cron

Since: 4.8.0

wp_using_themes()

Checks if themes should be loaded.

function wp_using_themes(): bool

Filter: wp_using_themes

Since: 5.1.0

wp_is_json_request()

Checks if request expects JSON response.

function wp_is_json_request(): bool

Since: 5.0.0

wp_is_jsonp_request()

Checks if request expects JSONP response.

function wp_is_jsonp_request(): bool

Since: 5.2.0

wp_is_xml_request()

Checks if request expects XML response.

function wp_is_xml_request(): bool

Since: 5.2.0

File Modification

wp_is_file_mod_allowed()

Checks if file modifications are allowed.

function wp_is_file_mod_allowed( string $context ): bool

Filter: file_mod_allowed

Since: 4.8.0

Early Translation Loading

wp_load_translations_early()

Loads translations before full WordPress init.

function wp_load_translations_early(): void

Purpose: For error messages during bootstrap

Since: 3.4.0

Byte Conversion

wp_convert_hr_to_bytes()

Converts PHP ini shorthand to bytes.

function wp_convert_hr_to_bytes( string $value ): int

Examples:

'40M' → 41943040
'1G' → 1073741824

Since: 2.3.0

wp_is_ini_value_changeable()

Checks if PHP ini value can be changed at runtime.

function wp_is_ini_value_changeable( string $setting ): bool

Since: 4.6.0

WordPress Loading Functions

Server Environment Functions

wp_get_server_protocol()

wp_fix_server_vars()

wp_populate_basic_auth_from_authorization_header()

Requirements Checking

wp_check_php_mysql_versions()

Environment Functions

wp_get_environment_type()

wp_get_development_mode()

wp_is_development_mode()

Maintenance Mode

wp_maintenance()

wp_is_maintenance_mode()

Timer Functions

timer_float()

timer_start()

timer_stop()

Debug Mode

wp_debug_mode()

Language Directory

wp_set_lang_dir()

Database Functions

require_wp_db()

wp_set_wpdb_vars()

Object Cache

wp_using_ext_object_cache()

wp_start_object_cache()

Installation Check

wp_not_installed()

Plugin Loading

wp_get_mu_plugins()

wp_get_active_and_valid_plugins()

wp_skip_paused_plugins()

Theme Loading

wp_get_active_and_valid_themes()

wp_skip_paused_themes()

Recovery Mode

wp_is_recovery_mode()

is_protected_endpoint()

is_protected_ajax_action()

Encoding

wp_set_internal_encoding()

wp_magic_quotes()

Shutdown

shutdown_action_hook()

Context Detection

is_login()

is_admin()

is_blog_admin()

is_network_admin()

is_user_admin()

is_multisite()

Utility Functions

absint()

get_current_blog_id()

get_current_network_id()

wp_installing()

is_ssl()

Request Detection

wp_doing_ajax()

wp_doing_cron()

wp_using_themes()

wp_is_json_request()

wp_is_jsonp_request()

wp_is_xml_request()

File Modification

wp_is_file_mod_allowed()

Early Translation Loading

wp_load_translations_early()

Byte Conversion

wp_convert_hr_to_bytes()

wp_is_ini_value_changeable()

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