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The HTTP specification allows browsers to perform conditional requests avoiding use of extra bandwidth if the page was not modified. In 43 Things I added support for conditional HTTP requests to some of our RSS feeds to save bandwidth.

As an alternative you can use the built-in page caching which uses the web server to automatically handle conditional requests, but this is not always appropriate. If you have content that is customized for a user, like home page links for logged-in users, the page cache won't work because different users will have different home page links. In our case it was simpler to add a few lines to our code than to set up a shared space to use as a page cache.

The solution I chose can be applied to any page you can determine a last modified time for.