import { Schema } from '../core/schema';
import { NullableType } from '../types/types';
export declare class BooleanSchema<Input extends NullableType<boolean> = boolean, Final = Input> extends Schema<Input, Final> {
    protected message: string;
    protected rule: (value: Input) => value is Input & boolean;
    /**
     * Checks if is true or false
     * @param mustBeValue
     * @param message @option Overrides default message
     */
    mustBe(mustBeValue: boolean, message?: string): import('..').ObjectPropertiesSchema<Input, this["final"]>;
}
export declare const boolean: <Input extends boolean = boolean, Final = any>(message?: string) => BooleanSchema<Input, Final>;