Published on 25 Jul 2007 at 10:23 pm.
Filed under Web stuff.

It seems that Yahoo has released a new Firefox extension for developers called Yslow. The purpose of this extension is to help rate the performance of a Web site. It does this by extending on the popular Firebug extension. A meta-extension if you will.

While I deeply appreciate the work of the Yahoo development team and think that this could be a very useful extension, this tool really needs some more polish. After just a few minutes of playing around with it I’ve found the following bugs:

  • Incorrectly lists CSS files as being outside of the HEAD element. This doesn’t happen all of the time.
  • Incorrectly lists ETags as being missing when they are not. By clicking on the ‘Stat’s button you can see all of the served out ETags.
  • Not really a bug, but not having an expires tag on every file shouldn’t constitute an F rating.
  • While I can’t be sure that they really aren’t, I find it odd that Akami, one of the leaders in Content Delivery Network (CDN), is listed as not using a CDN. Nor is the WWE, one of their clients.

I’ve seen many of these bugs on one of our client sites, Montgomery Chiropractic Center.

Beyond the bugs, one really has to question the fact that they weighed each proponent equally. Most web sites will never be Amazon level and thus will have no need for a CDN. True, having one will improve your site’s performance, but weighing it the same as setting Expires/ETag headers is just unrealistic.

Also, this tool is only useful for measuring sites that have a high percentage of returning visitors and does not score very highly for sites geared primarily for unique visitors that only view 1-2 pages before they leave. In those situations it would be preferable to not have any external CSS or JavaScript but better to have them all on one page to decrease the number of HTTP requests. Of course, for most Web sites you are going to want to compromise between these two so this tool only measuring the one is a bit poor.

Due to its bugs and a metric that lends itself to low scoring, I really don’t advice taking this extension too seriously right now. It can help point out some bugs and will be great in the future, but for now it’s not up to par. Then again, maybe this extension was really meant only for developers of Amazon-like level sites and isn’t for general Web developers, but if that’s so then they really should say that somewhere.

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