/**
 * Checks whether a string is a valid URL.
 * @param url - String to check.
 * @returns True if the string is a valid URL, false otherwise.
 * @internal
 */
export declare function isValidUrl(url: string): boolean;
/**
 * Checks whether a URL is existing via a head request.
 * @param url - URL to be checked.
 * @returns Promise - resolves if the URL exists.
 */
export declare function checkUrlExists(url: string): Promise<number>;