how does entity tag works?

ETag (entity tag) HTTP headers are used to verify that the client (such as a mobile device) is using the most recent version of a record. When a GET request is made, the ETag is returned as a response header. Thanks to the ETag, the client can also send conditional requests.

• In order to confirm that the client (such as a mobile device) has the most recent version of a record, an HTTP header called an ETag (entity tag) is utilised. The ETag is returned as a response header in response to a GET request. The client can also submit conditional requests thanks to the ETag.