The Vary HTTP header is sent in billions of HTTP responses every day. But its use has never fulfilled its original vision, and many developers misunderstand what it does or don’t even realize that their web server is sending it. With the coming of the Client Hints, Variants41 and Key38 specifications, varied responses are getting a fresh start.
The story of Vary starts with a beautiful idea of how the web should work. In principle, a URL represents not a web page, but a conceptual resource, like your bank statement. Imagine that you want to see your bank statement: You go to
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bank.com and send a