ETag

An identifier for this exact version of the resource.

Response header (sent by servers) conditional

How it works

Send it back in If-None-Match to save bandwidth (304), or in If-Match to update safely without overwriting someone else’s change (412).

Example

ETag: "33a64df5"

See it live: send any request in Endpoint Client and open the Headers tab, where every response header is explained. Specification: RFC 9110.

Related headers

If-Match

Only perform the change if the resource still has this ETag.

If-Modified-Since

Only send the body if it changed after this date.

If-None-Match

Only send the body if the ETag differs.

Last-Modified

When the resource last changed.