Core functions for error checking, termination, and error protection.

Source: wp-includes/load.php, wp-includes/functions.php, wp-includes/error-protection.php

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Error Checking

is_wp_error()

Checks whether a variable is a WP_Error instance.

function is_wp_error( mixed $thing ): bool

Since: 2.1.0
Source: wp-includes/load.php

Parameter	Type	Required	Description
$thing	mixed	Yes	Variable to check

Returns: true if $thing is a WP_Error instance.

Fires: is_wp_error_instance action (if true)

Example:

$result = wp_insert_post( $args );

if ( is_wp_error( $result ) ) {
    echo 'Error: ' . $result->get_error_message();
    return;
}

echo 'Post created with ID: ' . $result;

---

Execution Termination

wp_die()

Kills WordPress execution and displays an error message.

function wp_die( 
    string|WP_Error $message = '', 
    string|int $title = '', 
    string|array|int $args = array() 
): void

Since: 2.0.4
Source: wp-includes/functions.php

Parameter	Type	Required	Default	Description
$message	string|WP_Error	No	''	Error message or WP_Error object
$title	string|int	No	''	Error title (or response code if int)
$args	string|array|int	No	[]	Arguments (or response code if int)

Arguments:

Key	Type	Default	Description
response	int	500 (200 for Ajax)	HTTP response code
link_url	string	''	URL for a link
link_text	string	''	Text for the link
back_link	bool	false	Show "Back" link
text_direction	string	auto	'ltr' or 'rtl'
charset	string	'utf-8'	HTML charset
code	string	'wp_die'	Error code
exit	bool	true	Whether to exit after display

Handler selection:

Context	Filter	Default Handler
Ajax request	wp_die_ajax_handler	_ajax_wp_die_handler
JSON request	wp_die_json_handler	_json_wp_die_handler
JSONP REST	wp_die_jsonp_handler	_jsonp_wp_die_handler
XML-RPC	wp_die_xmlrpc_handler	_xmlrpc_wp_die_handler
XML/Feed	wp_die_xml_handler	_xml_wp_die_handler
Default	wp_die_handler	_default_wp_die_handler

Examples:

// Simple message
wp_die( 'You do not have permission to access this page.' );

// With title and response code
wp_die( 'Invalid request.', 'Error', 400 );

// With WP_Error
$error = new WP_Error( 'forbidden', 'Access denied.', array( 'status' => 403 ) );
wp_die( $error );

// With options
wp_die( 'An error occurred.', 'Error', array(
    'response'  => 500,
    'back_link' => true,
    'exit'      => true,
) );

// Without exiting
wp_die( 'Warning message.', '', array( 'exit' => false ) );
echo 'This still runs.';

---

Die Handlers (Internal)

_default_wp_die_handler()

Default handler that displays an HTML error page.

function _default_wp_die_handler( 
    string|WP_Error $message, 
    string $title = '', 
    string|array $args = array() 
): void

Since: 3.0.0
Access: Private

---

_ajax_wp_die_handler()

Handler for Ajax requests. Returns plain text.

function _ajax_wp_die_handler( 
    string $message, 
    string $title = '', 
    string|array $args = array() 
): void

Since: 3.4.0
Access: Private

Default response code: 200

---

_json_wp_die_handler()

Handler for JSON requests.

function _json_wp_die_handler( 
    string $message, 
    string $title = '', 
    string|array $args = array() 
): void

Since: 5.1.0
Access: Private

Response format:

{
    "code": "error_code",
    "message": "Error message",
    "data": {
        "status": 500
    },
    "additional_errors": []
}

---

_jsonp_wp_die_handler()

Handler for JSONP REST requests.

function _jsonp_wp_die_handler( 
    string $message, 
    string $title = '', 
    string|array $args = array() 
): void

Since: 5.2.0
Access: Private

---

_xmlrpc_wp_die_handler()

Handler for XML-RPC requests.

function _xmlrpc_wp_die_handler( 
    string $message, 
    string $title = '', 
    string|array $args = array() 
): void

Since: 3.2.0
Access: Private

---

_xml_wp_die_handler()

Handler for XML requests (feeds, trackbacks).

function _xml_wp_die_handler( 
    string $message, 
    string $title = '', 
    string|array $args = array() 
): void

Since: 5.2.0
Access: Private

Response format:

<error>
    <code>error_code</code>
    <title><![CDATA[Error Title]]></title>
    <message><![CDATA[Error message]]></message>
    <data>
        <status>500</status>
    </data>
</error>

---

_scalar_wp_die_handler()

Handler for simple scalar output.

function _scalar_wp_die_handler( 
    string $message = '', 
    string $title = '', 
    string|array $args = array() 
): void

Since: 3.4.0
Access: Private

---

_wp_die_process_input()

Processes arguments passed to wp_die() handlers.

function _wp_die_process_input( 
    string|WP_Error $message, 
    string $title = '', 
    string|array $args = array() 
): array

Since: 5.1.0
Access: Private

Returns: Array with [ $message, $title, $parsed_args ]

---

Error Protection Functions

wp_register_fatal_error_handler()

Registers the shutdown handler for fatal errors.

function wp_register_fatal_error_handler(): void

Since: 5.2.0
Source: wp-includes/error-protection.php

Only registers if wp_is_fatal_error_handler_enabled() returns true.

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wp_is_fatal_error_handler_enabled()

Checks whether the fatal error handler is enabled.

function wp_is_fatal_error_handler_enabled(): bool

Since: 5.2.0
Source: wp-includes/error-protection.php

Returns: true if enabled, false if disabled.

Disabled by:

• WP_DISABLE_FATAL_ERROR_HANDLER constant
• wp_fatal_error_handler_enabled filter

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wp_recovery_mode()

Access the WordPress Recovery Mode instance.

function wp_recovery_mode(): WP_Recovery_Mode

Since: 5.2.0
Source: wp-includes/error-protection.php

Returns: Singleton WP_Recovery_Mode instance.

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wp_paused_plugins()

Gets the storage instance for paused plugins.

function wp_paused_plugins(): WP_Paused_Extensions_Storage

Since: 5.2.0
Source: wp-includes/error-protection.php

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wp_paused_themes()

Gets the storage instance for paused themes.

function wp_paused_themes(): WP_Paused_Extensions_Storage

Since: 5.2.0
Source: wp-includes/error-protection.php

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wp_get_extension_error_description()

Gets a human-readable description of an extension’s error.

function wp_get_extension_error_description( array $error ): string

Since: 5.2.0
Source: wp-includes/error-protection.php

Parameter	Type	Required	Description
$error	array	Yes	Error from error_get_last()

Returns: Formatted error description string.

Example output:

An error of type E_ERROR was caused in line 123 of the file /path/to/file.php. Error message: Call to undefined function foo()

---

Usage Patterns

Function Return Pattern

function my_function( $id ) {
    if ( empty( $id ) ) {
        return new WP_Error( 'missing_id', 'ID is required.' );
    }
    
    $result = get_post( $id );
    
    if ( ! $result ) {
        return new WP_Error( 'not_found', 'Post not found.', array( 'status' => 404 ) );
    }
    
    return $result;
}

// Caller
$post = my_function( $id );
if ( is_wp_error( $post ) ) {
    wp_die( $post );
}

Ajax Error Response

add_action( 'wp_ajax_my_action', function() {
    if ( ! current_user_can( 'edit_posts' ) ) {
        wp_die( 'Unauthorized', '', 403 );
    }
    
    $result = do_something();
    
    if ( is_wp_error( $result ) ) {
        wp_send_json_error( array(
            'code'    => $result->get_error_code(),
            'message' => $result->get_error_message(),
        ) );
    }
    
    wp_send_json_success( $result );
} );

Custom wp_die Handler

add_filter( 'wp_die_handler', function( $handler ) {
    return function( $message, $title, $args ) {
        // Log errors
        error_log( "wp_die called: $message" );
        
        // Call original handler
        _default_wp_die_handler( $message, $title, $args );
    };
} );