diff --git a/wp-includes/rest-api.php b/wp-includes/rest-api.php
index e408522ab6..dc55af08f3 100644
--- a/wp-includes/rest-api.php
+++ b/wp-includes/rest-api.php
@@ -1250,6 +1250,7 @@ function rest_get_avatar_sizes() {
  * @since 5.5.0 Add the "uuid" and "hex-color" formats.
  *              Support the "minLength", "maxLength" and "pattern" keywords for strings.
  *              Validate required properties.
+ *              Support the "minItems" and "maxItems" keywords for arrays.
  *
  * @param mixed  $value The value to validate.
  * @param array  $args  Schema array to use for validation.
@@ -1287,6 +1288,16 @@ function rest_validate_value_from_schema( $value, $args, $param = '' ) {
 				return $is_valid;
 			}
 		}
+
+		if ( isset( $args['minItems'] ) && count( $value ) < $args['minItems'] ) {
+			/* translators: 1: Parameter, 2: number. */
+			return new WP_Error( 'rest_invalid_param', sprintf( __( '%1$s must contain at least %2$s items.' ), $param, number_format_i18n( $args['minItems'] ) ) );
+		}
+
+		if ( isset( $args['maxItems'] ) && count( $value ) > $args['maxItems'] ) {
+			/* translators: 1: Parameter, 2: number. */
+			return new WP_Error( 'rest_invalid_param', sprintf( __( '%1$s must contain at most %2$s items.' ), $param, number_format_i18n( $args['maxItems'] ) ) );
+		}
 	}
 
 	if ( 'object' === $args['type'] ) {
diff --git a/wp-includes/rest-api/endpoints/class-wp-rest-controller.php b/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
index a2d1134f11..0d1e85cbf1 100644
--- a/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
+++ b/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
@@ -643,6 +643,8 @@ abstract class WP_REST_Controller {
 			'minLength',
 			'maxLength',
 			'pattern',
+			'minItems',
+			'maxItems',
 		);
 
 		foreach ( $schema_properties as $field_id => $params ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b264bea2b0..94cb1e9791 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-47922';
+$wp_version = '5.5-alpha-47923';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.