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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

7 May

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)

Barry Pollard

@tunetheweb.com

7 May

It actually came from Speculation Rules initially (we wanted to give the ability to not waste speculations if unimportant params were used). Extending it to the browser’s HTTP Cache is a nice addition. E.g. - Visit home page with UTM params - Visit other page - Click logo to go home (without UTMs)

Barry Pollard

@tunetheweb.com

And yes many CDNs have been able to do this, but in non-standard ways. It’s nice to have a standard way for sites to inform any CDN which params matter. No aware of any that have implemented support yet but have spoken to people at some of them who’ve said they are interested in it.

7/5/26, 9:36 pm0 reposts2 likes

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