You will need to use `"POST"` in order to be able to send a JSON body to the `_search` endpoint; as far as I am aware, `MSXML2.ServerXMLHTTP` cannot send a request body with `"GET"`. I'd also recommend setting

xml.setRequestHeader "Content-Type", "application/json"

If you need to interact with Elasticsearch from Classic ASP more than this, you might be able to save yourself some considerable time by creating a [COM Callable Wrapper]( and using COM interop with [the .NET client to interact with Elasticsearch.](