Testing Your Site using Yahoo!’s YSlow

January 6, 2009
This entry is part 1 of 2 in the series Speeding Up Web Sites using Yahoo!'s YSlow

On Yahoo!’s Developer pages you can find the YSlow plug-in for the Firefox Web browser (the plug-in works in conjunction with Firebug, which you should probably already be using anyway). After installing YSlow (and Firebug, if you haven’t already), restart Firefox, then load your Web page in Firebox. Click on the YSlow icon in the lower-right corner of the browser window, and you’ll see:

  • A “report card” for the page’s performance
  • The files and images loaded on that page, including JavaScript and CSS
  • Listings of specific strengths and weaknesses of the page

Using the built-in YSlow tools, you can also view: page statistics (total size of all files, number of HTTP requests made, etc.), all of the CSS compiled together, and all of the JavaScript involved. You can even test the JavaScript using JSLint. For more on using YSlow, check out its documentation or this screencast.

In case you’re curious, when I tested my site’s home page, I got a ‘B’ (85), which is a decent start. To improve the performance, I need to add expiration headers, use a CDN, and add ETags. And, to be honest, I didn’t even know what these last two were!

Update: I’ve started fixing some of the issues addressed by YSlow. You can read about that process in this other post.