[dev-platform] Intent to Prototype: No-Vary-Search HTTP Caching Extension

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Sunil Mayya

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May 5, 2026, 4:42:38 PM (21 hours ago) May 5

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We intend to prototype support for the No-Vary-Search HTTP caching extension in Firefox.

Specification

No-Vary-Search (IETF httpbis): https://httpwg.org/http-extensions/draft-ietf-httpbis-no-vary-search.html

Summary

The No-Vary-Search specification defines a new HTTP response header, No-Vary-Search, that allows servers to declare which URL query parameters should be ignored when matching cache entries. This enables the browser to serve a cached response for a URL even when query parameters differ, as long as the server has declared those parameters do not affect the response.

For example, given the response header:

No-Vary-Search: params=("utm_source" "utm_medium" "utm_campaign")

If the browser has a cached response for https://example.com/article, it will also serve that cached response for:

https://example.com/article?utm_source=email, and https://example.com/article?utm_source=social&utm_medium=paid&utm_campaign=summer

But not for https://example.com/article?ref=homepage

Because ref is not declared as ignorable, it still causes a cache miss.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=2037149

Mozilla Standards Position: https://github.com/mozilla/standards-positions/issues/717 (Positive)

Other Browsers

Chrome: Shipped (Chrome 141, HTTP disk cache)

Safari: No position (https://github.com/WebKit/standards-positions/issues/106)

Platform Coverage

All

Web Platform Tests

https://wpt.fyi/results/?label=master&label=experimental&aligned&q=no-vary-search

Sunil Mayya

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6:08 AM (7 hours ago) 6:08 AM

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Summary:

Today, two URLs that differ only in query parameters irrelevant to the response content (https://example.com/article?ref=homepage and https://example.com/article?ref=sidebar) are treated as separate cache entries, causing redundant network requests even when the server returns identical content. The No-Vary-Search HTTP response header lets servers declare which query parameters are irrelevant to the response, allowing the browser to reuse cached entries across those URL variants. This reduces unnecessary network traffic and improves page load performance for users, with no changes required from web developers beyond a single response header. No-Vary-Search is also used extensively by the Speculation Rules API, where it allows speculative prefetches to match navigations to URLs that differ only in declared-irrelevant query parameters.

Bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=2037149

Specification:

https://httpwg.org/http-extensions/draft-ietf-httpbis-no-vary-search.html

Standards Body:

IETF (httpbis)

Platform Coverage:

All

Preference:

network.http.no-vary-search.enabled

DevTools Bug:

N/A