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Apache: Detecting WebP support with Header Vary Accept
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTP_ACCEPT} image/webp
RewriteCond %{DOCUMENT_ROOT}/$1.webp -f
RewriteRule (.+)\.(jpe?g|png)$ $1.webp [T=image/webp,E=accept:1]
<IfModule mod_headers.c>
Header append Vary Accept env=REDIRECT_accept
AddType image/webp .webp

sergejmueller commented May 2, 2013

The code is implemented on

I see that you're adding 'Accept' to the Vary header, which is great, but you're also varying the content based on the User-Agent, so that would have to be included in the Vary header for it to be correct.

Fortunately Chrome is now sending "image/webp" in the Accept header for image requests, (although not on html requests unfortunately) so you should be able to remove the User-Agent detection. Users will get the webp version for resources included on a page, but not if they request the image directly.

Sergej: Just checked your website, but in the latest Chrome Beta I see PNG's. Is this .htacess not working any more?


sergejmueller commented Nov 24, 2013


Sorry I didn't see your link in time as its expired. When I check in Chrome 35 Beta (osx) its still PNG's your site is serving.

maniqui commented Feb 24, 2015

@musikdk, you probably see a .png files because that's what the URL in the page points to. But the server is serving an webp image "disguised" as a file with extension .png. It's an internal rewrite.

jslegers commented Dec 9, 2015

What exactly is this code supposed to do?

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