Core functions for route registration, URL handling, and utilities.

Source: wp-includes/rest-api.php

Route Registration

register_rest_route()

Registers a REST API route. Must be called during rest_api_init action.

register_rest_route( string $route_namespace, string $route, array $args = array(), bool $override = false ): bool

Args:

Returns: true on success, false on error.

Example:

add_action( 'rest_api_init', function() {
    register_rest_route( 'my-plugin/v1', '/items/(?P<id>d+)', array(
        'methods'             => 'GET',
        'callback'            => 'get_item',
        'permission_callback' => '__return_true',
        'args'                => array(
            'id' => array(
                'type'              => 'integer',
                'required'          => true,
                'validate_callback' => fn( $v ) => $v > 0,
            ),
        ),
    ) );
} );

register_rest_field()

Registers a new field on an existing object type.

register_rest_field( string|array $object_type, string $attribute, array $args = array() ): void

Args:

Example:

register_rest_field( 'post', 'custom_meta', array(
    'get_callback' => fn( $post ) => get_post_meta( $post['id'], 'custom_key', true ),
    'update_callback' => fn( $value, $post ) => update_post_meta( $post->ID, 'custom_key', $value ),
    'schema' => array(
        'type'        => 'string',
        'description' => 'Custom metadata field',
    ),
) );

URL Functions

rest_url()

Retrieves the URL to a REST endpoint.

rest_url( string $path = '', string $scheme = 'rest' ): string

Returns: Full URL to the endpoint.

Example:

rest_url( '/wp/v2/posts' );
// https://example.com/wp-json/wp/v2/posts

get_rest_url()

Retrieves the URL to a REST endpoint on a site.

get_rest_url( int $blog_id = null, string $path = '/', string $scheme = 'rest' ): string

Returns: Full URL to the endpoint.

rest_get_url_prefix()

Retrieves the REST URL prefix.

rest_get_url_prefix(): string

Returns: URL prefix, default wp-json.

Request/Response Functions

rest_do_request()

Performs an internal REST API request.

rest_do_request( WP_REST_Request|string $request ): WP_REST_Response

Returns: Response from the endpoint.

Example:

$request = new WP_REST_Request( 'GET', '/wp/v2/posts' );
$request['per_page'] = 5;
$response = rest_do_request( $request );
$posts = $response->get_data();

rest_get_server()

Retrieves the current REST server instance.

rest_get_server(): WP_REST_Server

Returns: The global WP_REST_Server instance.

rest_ensure_request()

Ensures a request is a WP_REST_Request object.

rest_ensure_request( WP_REST_Request|array|string $request ): WP_REST_Request

Returns: WP_REST_Request instance.

rest_ensure_response()

Ensures a response is a WP_REST_Response object.

rest_ensure_response( WP_REST_Response|WP_Error|WP_HTTP_Response|mixed $response ): WP_REST_Response|WP_Error

Returns: WP_REST_Response or WP_Error.

rest_convert_error_to_response()

Converts a WP_Error to a WP_REST_Response.

rest_convert_error_to_response( WP_Error $error ): WP_REST_Response

Returns: Response with error data, status from error’s status data.

Validation Functions

rest_validate_request_arg()

Validates a request argument based on route args.

rest_validate_request_arg( mixed $value, WP_REST_Request $request, string $param ): true|WP_Error

Returns: true if valid, WP_Error if invalid.

rest_sanitize_request_arg()

Sanitizes a request argument based on route args.

rest_sanitize_request_arg( mixed $value, WP_REST_Request $request, string $param ): mixed

Returns: Sanitized value.

rest_parse_request_arg()

Parses a request argument based on type.

rest_parse_request_arg( mixed $value, WP_REST_Request $request, string $param ): mixed|WP_Error

rest_validate_value_from_schema()

Validates a value against a JSON Schema.

rest_validate_value_from_schema( mixed $value, array $args, string $param = '' ): true|WP_Error

Returns: true if valid, WP_Error if invalid.

rest_sanitize_value_from_schema()

Sanitizes a value based on JSON Schema.

rest_sanitize_value_from_schema( mixed $value, array $args, string $param = '' ): mixed

Returns: Sanitized value.

rest_get_allowed_schema_keywords()

Gets supported JSON Schema keywords.

rest_get_allowed_schema_keywords(): string[]

Returns: Array of supported keywords like type, enum, minimum, pattern, etc.

Type Checking Functions

rest_is_boolean()

Determines if a value is boolean-like.

rest_is_boolean( mixed $maybe_bool ): bool

Accepts: true, false, 'true', 'false', 1, 0, '1', '0', 'yes', 'no'.

rest_sanitize_boolean()

Sanitizes a value to boolean.

rest_sanitize_boolean( mixed $value ): bool

rest_is_integer()

Determines if a value is an integer or integer string.

rest_is_integer( mixed $maybe_integer ): bool

rest_is_array()

Determines if a value is array-like.

rest_is_array( mixed $maybe_array ): bool

rest_sanitize_array()

Sanitizes a value to an array.

rest_sanitize_array( mixed $maybe_array ): array

rest_is_object()

Determines if a value is object-like.

rest_is_object( mixed $maybe_object ): bool

rest_sanitize_object()

Sanitizes a value to an object/associative array.

rest_sanitize_object( mixed $maybe_object ): array

Date Functions

rest_parse_date()

Parses an RFC 3339 date string.

rest_parse_date( string $date, bool $force_utc = false ): int|false

Returns: Unix timestamp or false on failure.

rest_get_date_with_gmt()

Parses a date into local and GMT times.

rest_get_date_with_gmt( string $date, bool $is_utc = false ): array|null

Returns: Array with date and date_gmt keys, or null.

Utility Functions

rest_is_ip_address()

Validates an IP address string.

rest_is_ip_address( string $ip ): string|false

Returns: IP address if valid, false otherwise.

rest_parse_hex_color()

Parses and validates a hex color.

rest_parse_hex_color( string $color ): string|false

Returns: 6-character hex with #, or false.

rest_get_avatar_urls()

Retrieves avatar URLs for a user.

rest_get_avatar_urls( mixed $id_or_email ): array

Returns: Array of size => URL pairs.

rest_get_avatar_sizes()

Retrieves available avatar sizes.

rest_get_avatar_sizes(): int[]

Returns: Default array( 24, 48, 96 ).

rest_authorization_required_code()

Gets appropriate HTTP status for unauthorized requests.

rest_authorization_required_code(): int

Returns: 401 if not logged in, 403 if logged in.

wp_is_rest_endpoint()

Checks if the current request is a REST API request.

wp_is_rest_endpoint(): bool

Returns: true if REST request, false otherwise.

Route Lookup Functions

rest_get_route_for_post()

Gets the REST route for a post.

rest_get_route_for_post( WP_Post|int $post ): string

Returns: Route like /wp/v2/posts/123.

rest_get_route_for_post_type_items()

Gets the REST route for a post type’s collection.

rest_get_route_for_post_type_items( string $post_type ): string

Returns: Route like /wp/v2/posts.

rest_get_route_for_term()

Gets the REST route for a term.

rest_get_route_for_term( WP_Term|int $term ): string

Returns: Route like /wp/v2/categories/5.

rest_get_route_for_taxonomy_items()

Gets the REST route for a taxonomy’s collection.

rest_get_route_for_taxonomy_items( string $taxonomy ): string

Returns: Route like /wp/v2/categories.

rest_get_queried_resource_route()

Gets the REST route for the currently queried resource.

rest_get_queried_resource_route(): string

Returns: Route for current post, term, or author.

Response Filtering

rest_filter_response_fields()

Filters response to only include requested fields.

rest_filter_response_fields( WP_REST_Response $response, WP_REST_Server $server, WP_REST_Request $request ): WP_REST_Response

Respects _fields query parameter.

rest_is_field_included()

Checks if a field should be included in response.

rest_is_field_included( string $field, array $fields ): bool

Example:

rest_is_field_included( 'title.rendered', array( 'title' ) ); // true
rest_is_field_included( 'content', array( 'title' ) );        // false

rest_filter_response_by_context()

Filters response data by schema context.

rest_filter_response_by_context( array $response_data, array $schema, string $context ): array

Returns: Filtered response data.

rest_default_additional_properties_to_false()

Sets additionalProperties: false on all object schemas.

rest_default_additional_properties_to_false( array $schema ): array

Preloading

rest_preload_api_request()

Preloads REST API data to avoid additional requests.

rest_preload_api_request( array $memo, string $path ): array

Example:

$preload_paths = array(
    '/wp/v2/posts?per_page=5',
    '/wp/v2/users/me?context=edit',
);
$preload_data = array_reduce( $preload_paths, 'rest_preload_api_request', array() );
wp_add_inline_script( 'my-script', 'var preloadedData = ' . wp_json_encode( $preload_data ) );

rest_parse_embed_param()

Parses the _embed parameter.

rest_parse_embed_param( string|array $embed ): bool|string[]

Returns: true for all links, or array of relation names.

Schema Endpoints

rest_get_endpoint_args_for_schema()

Converts schema to endpoint args.

rest_get_endpoint_args_for_schema( array $schema, string $method = WP_REST_Server::CREATABLE ): array

Returns: Args array suitable for register_rest_route().