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The "YSlow Rules" Lesson is part of the full, Website Performance course featured in this preview video. Here's what you'd learn in this lesson:
YSlow is one of the first browser plugins that allowed developers to test the performance of a website. YSlow uses a set of rules to gauge the performance. The first rule is fewer HTTP requests. The next YSlow rule is to use a CDN. CDN’s have multiple locations all over the world and can take advantage of shared caching. Using expires and cache-control headers give you the ability to control the loading policy around stable content. Gzipping can compress your content anywhere from 50%-70% decreasing loading time.