Conditional requests (ETag, Last-Modified, 304)
type: TechArticle
description: Send a validator — ETag or Last-Modified — on every cacheable response, and honour If-None-Match / If-Modified-Since so unchanged resources return an empty 304 instead of the full body.
language: en
is part of: Web Specification Studio
author: Web Specification Studio
publisher: Web Specification Studio
license: https://creativecommons.org/licenses/by/4.0/
date modified: 2026-06-09T11:00:00.000Z
citation: RFC 9110 §13 — Conditional Requests
  type: CreativeWork
  publisher: IETF
citation: RFC 9110 §8.8 — Validator Fields (ETag, Last-Modified)
  type: CreativeWork
  publisher: IETF
citation: MDN — HTTP conditional requests
  type: CreativeWork
  publisher: MDN
citation: MDN — 304 Not Modified
  type: CreativeWork
  publisher: MDN

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item list element: Conditional requests (ETag, Last-Modified, 304)
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  item: https://webspecification.com/spec/performance/conditional-requests/