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up.protocol ETag
HTTP header

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:

ETag: W/"55e4d42a148795d9f25f89d4"

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 [up-etag] attributes.