Cloudflare Adds HTTP Vary Header Support to Cache Rules for Websites on All Plans

What happened

On September 22, 2026, Cloudflare published a blog post by Alex Krivit and Zaidoon Abd Al Hadi announcing support for the HTTP Vary response header. Cloudflare said the feature is now available in Cache Rules on all plans. The post also quotes a description of Vary as "the ugliest part of HTTP that we haven't yet improved.", showing how awkward this header has long been to handle.

Some background helps. A cache is a store of ready-made copies of web pages and files. A CDN (content delivery network) such as Cloudflare keeps these copies so visitors can be answered quickly without asking the website's own server, called the origin, every time. When a browser asks for a page, it sends request headers: short notes such as its preferred language or the file formats it accepts. According to Cloudflare, Vary is a standard HTTP response header that tells intermediary caches like a CDN which of those request fields may affect the origin's response. Sites commonly use it to serve different languages, image formats, compression methods or regional content at the same URL.

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Why Vary is hard to handle

Cloudflare uses examples to describe the dilemma. If a cache ignores Vary, the HTML and JSON versions of the same URL may go to the wrong clients. For example, an app expecting data could receive web page markup it cannot parse. If instead a cache treats every raw header value as distinct, a handful of similar requests can scatter into thousands of stored copies that are almost never reused. In one example, two Accept-Language values (the header that states language preferences) differ in order and language tags. According to Cloudflare, both effectively prefer English, so the origin may return the same English response, but the cache stores them separately because the raw values differ.

Cloudflare notes that one field with 10 values produces 10 variants, while three fields with 10 values each can produce 1,000 combinations. These scattered variants take up storage space, push one another out of the cache and lower the cache hit ratio, which is the share of requests answered from stored copies. They also send more requests back to the origin. An analysis cited by Cloudflare examined more than 120 million responses from nearly 50,000 popular websites. It found that nearly 3,000 sites vary on four or more fields, some on 10, 23 or even 47.

How Cache Rules handle Vary

Cloudflare says the new design splits the decision in two. The origin uses Vary to indicate which request headers may affect the response, and the Cache Rule decides how Cloudflare treats each header's values. If the origin does not return Vary, Cloudflare caches as usual. Headers without an individual setting fall back to the rule's default action.

What it means for readers and site administrators

For everyday internet users, changes like this happen behind the scenes. Cloudflare says Vary exists to stop a cache from handing a visitor the wrong version of a page, such as the wrong language or format. For site administrators, Cloudflare says earlier approaches to such content each had a limitation. Bypassing the cache gives up caching, and custom cache keys duplicate application logic. Workers require extra code, while Vary for images covers only a narrower use case. Cloudflare says the new feature is meant to fill the gaps between them.

The feature details and benefits above are Cloudflare's own description in its announcement. Actual results depend on each site's configuration and traffic. This article only summarizes the announcement and does not constitute a recommendation to buy any product or service.

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