[Yandex Cloud documentation](../../../index.md) > [Yandex Object Storage](../../index.md) > API reference > [AWS S3 REST](../index.md) > [REST](index.md) > Common response headers

# Common response headers

Apart from the [standard HTTP headers](https://en.wikipedia.org/wiki/List_of_HTTP_header_fields), Yandex Object Storage uses additional response headers.

The table below describes additional headers as well as standard headers requiring clarification.

Header | Description
----- | -----
`ETag` | [MD5 hash](https://en.wikipedia.org/wiki/MD5) of an object if the object is uploaded as a single file. If the object is uploaded as a [multipart upload](../../concepts/multipart.md), then to calculate the `ETag` value, you need to get the MD5 hash sum of the uploaded parts (`MD5_sum`) and add the number of parts (`N`) to the resulting string: `"MD5_sum-N"`.<br/><br/>It does not include object metadata.
`X-Amz-Request-Id` | Unique request ID.<br/><br/>You may need it when contacting the Yandex Cloud support service if any problems occur.

If a request is sent with CORS headers, the response may contain [headers for a response](object/options.md#response-headers) to the `options` preflight request.

#### See also {#see-also}

* [Getting started with the AWS S3 API in Yandex Object Storage](../s3-api-quickstart.md)

* [Debugging requests using the AWS CLI](../signing-requests.md#debugging)

* [Example of sending a signed request using curl](../../api-ref/authentication.md#s3-api-example)

* [Code example for generating a signature](../../concepts/pre-signed-urls.md#code-examples)