Google Reader, considered by many to be the ultimate tool for keeping up with many blog and news feeds at once, has just made it possible to keep track of changes on web sites without subscribable RSS feeds. To do this, users can create “custom feeds” that include any kind of updates. Launched today, this capability should come in handy especially for e-commerce sites that may be adding new products or holding sales; company sites that publish press releases and new developments; and gaming sites showcasing new offerings. The potential is pretty unlimited. To create a custom feed, all you have to do is paste the URL in question into Reader’s existing “Add a Subscription” text field. When you click on “Create a Feed,” you are instructing Reader to check in on the site and suss out the differences between the current product and when you last checked. It provides a listing of these changes as snippets in Reader’s usual format. Here’s an example:

Because you are technically creating a feed where none existed before, you can use Google Reader to give you what you need to follow feedless pages using Bloglines, NewsGator or any other feed reader of your choice. The customized RSS is that clean. Google Reader isn’t the first tool to monitor web site updates — ChangeDetection.com got their first, but it obviously doesn’t have the brand recognition. Responding to previous efforts, web sites have started to alter their code so that people still can’t subscribe. Google also allows these sites to opt out of this new system. It will be interesting to see which web properties choose this option and why.