This response header contains a hash identifying the content in the response body.
Typically, the ETag value is a hash of the underlying data that was rendered, or a hash of the data's last modification time.
ETags can be used to prevent unnecessary re-rendering of unchanged content. See Conditional requests for details and examples.
A (weak) ETag typically looks like this:
For more information about an ETag's format, see MDN and RFC 7232.
Instead of sending this header, the server may also render fragments with