The MaxCDN Company Blog

YSlow for Firebug is a Firefox plug in launched by Yahoo! to find and point out the areas where a website can be further optimized. The YSlow is an open source solution which was first created internally by Yahoo! for benchmarking the performance of its own websites and later released for public usage. Working of YSlow YSlow actually works like a grader and gauges the performance of the webpages, and also provides a set of solutions which can pin point and improve the website performance. It comes with an inbuilt set of rules and also provides tools like Smush.it and JSLint. Checking performance of your CDN The second rule itself in the grading suggests making use of CDN for improved performance. YSlow has a slight drawback that it does not understand the performance of the CDN services unless the user explicitly configures the YSlow client for this. While, it comes with a wide range of popular CDN solutions, the list only covers the solutions that Yahoo! uses and hence list is not exhaustive. Nevertheless, YSlow allows configuring of the other CDN providers by going to the “About:Config” in Firefox and entering the string preference by selecting a New String Preference, where the CDN name can be entered as the string value. Multiple CDN providers can be entered by specifying them using comma as separator. Final Verdict: All in all, though it needs to be configured a bit, specifically when it comes to tracking CDN performance; with the brand name of Yahoo! and an open-source solution, which works seamlessly with the popular Firefox browser, YSlow is definitely one of the grading tools that should be used for checking the performance of the website and optimizing it further. From the YSlow FAQ: How do I add my CDN hostname to YSlow for Rule 2? Rule 2 says to use a content delivery network (CDN). The score for this rule is computed by checking the hostname of each component against the list of known CDNs. Unfortunately, the list of “known CDNs” are the ones used by Yahoo!. Most likely these are not relevant to your web site, except for potentially yui.yahooapis.com. If you want an accurate score for your web site, you can add your CDN hostnames to YSlow using Firefox’s preferences. Here are the steps to follow: 1. Go to about:config in Firefox. You’ll see the current list of preferences. 2. Right-click in the window and choose New and String to create a new string preference. 3. Enter extensions.yslow.cdnHostnames for the preference name. 4. For the string value, enter the hostname of your CDN, for example, mycdn.com. 5. Restart Firefox. Do not use quotes. If you have multiple CDN hostnames, separate them with commas. If you specify CDN hostnames in your preferences, they’ll be shown under the details for Rule 2 in the Performance view.