[glawrence13]

This is definitely one of our hard problems. There are some optimizations -- e-tags / last modified headers, comparing page content hashes -- but there's also only so much you can do before you just have to check the page again.

[AznHisoka]

Last modified headers is always set to the current time in the majority of cases, and it also requires a web request too (albeit a HEAD request would likely suffice)