that&#x27;s 2 dns lookups on any user that hasn&#x27;t already done that somewhere in the past and had it cached.<p>The question then is how likely are they to have done that in regards to your particular cdn and version of the library.<p>I agree that a lot of possible cdns, versions and so forth decreases the value of the common CDN approach, but there are at least some libraries that have a canonical CDN (JQuery for example) and not using that is essentially being the selfish player in a games theory style game.<p>Since I don&#x27;t know of any long running tracking of CDN usage that allows you to predict how many people who visit your site are likely to have a popular library in their cache it&#x27;s really difficult to talk about it meaningfully (I know there are one-off evaluations done in one point in time but that&#x27;s not really helpful).<p>Anyway it&#x27;s my belief that widespread refusal to use CDN versions of popular libraries is of course beneficial in the short run for the individual site but detrimental in the long run for a large number of sites.