This is especially valid as the Google server sends a far-future expires header (see below), so as soon as the browser has the file in its cache it won't even t

This is especially valid as the Google server sends a far-future expires header (see below), so as soon as the browser has the file in its cache it won't even try to contact the Google server for a new version of the file. So even if Google's servers go down, the browser will still use its locally available file (even without a possible delay, when waiting for a timeout). $ curl -I ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js HTTP/1.1 200 OK [...] Expires: Sat, 07 Dec 2013 05:29:17 GMT [...]