ETag or entity tag is part of HTTP, the protocol for the World Wide Web. It is one of several mechanisms that HTTP provides for web cache validation, which allows a client to make conditional requests. This allows caches to be more efficient, and saves bandwidth, as a web server does not need to send a full response if the content has not changed. ETags can also be used for optimistic concurrency control, as a way to help prevent simultaneous updates of a resource from overwriting each other. This is relevant to support central systems from fetching only new data about metrics. https://en.wikipedia.org/wiki/HTTP_ETag