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Harry Roberts
@csswizardry.com

I’ve been working with a client who runs a lot of social media and ad campaigns, so we’ve been deploying the experimental `No-Vary-Search HTTP` header. It’s amazing to see it actually working! Read all about it here: csswizardry.com/2026/05/bett...

csswizardry.comBetter Browser Caching with No-Vary-Search – CSS WizardryNo-Vary-Search lets HTTP caches ignore irrelevant query parameters such as UTM tags, while still keeping meaningful ones like product variants in the cache key.
John Wards
@johnwards.bsky.social

Trying to wrap my head around why this impacts browser. Because for advertising campaigns it’s likely an edge you click on 2 links with different utm for the same page? CDN cache it makes sense, but cdns could do this before right? Pretty sure I could do something like this in CF (might be wrong)

Harry Roberts
@csswizardry.com

It’s potentially an edge case, yes. And thus far more effective at CDN-level, yes. But in the case of things like ecomm filters and such (?sort, ?filter), having them in different orders could be wasteful. And very-frequently visited URLs (think BBC News homepage), there could be many lines in.

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Harry Roberts
@csswizardry.com

This is a bad example as a news homepage shouldn’t reeeeeally hit HTTP cache very often anyway. But for definite it’s a worthwhile additional layer if you’ve got everything else sorted.