Response
ETag
Provides a unique identifier for a specific version of a resource, enabling efficient conditional requests.
Syntax
ETag: "<etag_value>" | W/"<etag_value>"Example
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4"Description
ETag (Entity Tag) provides a unique identifier for a resource version. Browsers send it back via If-None-Match for 304 Not Modified responses.
Can be strong (exact match) or weak (prefixed with W/). Strong ETags required for byte-range requests.
More precise than Last-Modified. Most servers generate ETags automatically.
How real sites send this header
Home-page responses of 502 popular sites from the enterno.io /check catalogue, checked in the last 30 days.
31.9%
(160 of 502) send ETag.
See it on: yandex.ru, github.com, habr.com, beget.com, angular.dev
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