> For the complete documentation index, see [llms.txt](https://docs.coldstack.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.coldstack.io/http-api-compatible-with-amazon-s3/api-reference/common-response-headers.md).

# Common response headers

In addition to [standard HTTP headers,](https://en.wikipedia.org/wiki/List_of_HTTP_header_fields) ColdStack uses additional headers that may be present in responses.

Additional headings are described in the table below, as well as standard headings for which additional explanation is required.

| Heading            | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `ETag`             | <p><a href="https://ru.wikipedia.org/wiki/MD5">MD5 hash of the</a> object, if the object is loaded as a single file. If the object is loaded using a <a href="/pages/-MWtO76juk_huxULp3uu">compound load</a> , then for the calculation <code>ETag</code>it is necessary to obtain the MD5 hash from the sum of the MD5 hashes of the loaded parts (let's call it <code>MD5\_sum</code>) and attach the number of parts ( <code>N</code>): to the resulting string <code>"MD5\_sum-N"</code>.<br><br>Does not include object metadata.</p> |
| `x-amz-request-id` | <p>Unique identifier for the request.<br><br>It may be needed when contacting ColdStack support in case of problems.</p>                                                                                                                                                                                                                                                                                                                                                                                                                   |