Attributed viewpoint

Cloudflare previously ignored Vary for non-image responses

Before the new feature, Cloudflare ignored the Vary header on responses other than images, risking incorrect cache sharing—e.g., caching a JSON response and serving it to a client expecting HTML.

Simon Willison·Published Sep 23, 2026

Behind the viewpoint

Translations are for reading; original excerpts remain the evidence.

Comment: We just shipped support for the ugliest part of HTTP: Vary

Original excerpt

This used to be impossible to deploy behind Cloudflare caching, because they ignored the Vary header on anything other than images - so you risked caching the JSON version and then serving it up to someone who was expecting HTML.

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