/**
 * Checks if the input object is a valid Cloud Event.
 * A valid Cloud Event is a JSON object that contains id, source, type, and specversion.
 * See https://github.com/cloudevents/spec/blob/v1.0/spec.md#required-attributes
 * @param str input object
 * @returns true if the object is a valid Cloud Event
 */
export declare function isCloudEvent(obj: object): boolean;