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aaah that visit the same page again but without the prams example makes it click, much more likely than what I was thinking about in terms of two different UTMs. Neat, thanks!

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.

Curious if you’ve seen real world impacts on it, but I’m removed from B2C scale for a while now so it’s only a passing interest.

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.

I hit surprising wins with No-Vary-Search on faceted search pages, but only after normalizing param order server side. Otherwise cache hit rate looked random because semantically identical URLs stayed distinct.

This is the way 😍

this is the kind of spec that makes me happy. utm params destroying cache ratios for years, and the fix is a header. love when something so simple just works.