YSlow is a Firebug plug-in for measuring the overall performance of a web page and making recommendations to improve its speed. This is cool on a few levels:

• This is a great way to get an overview of the performance of a page, with links to helpful pages explaining what’s going on. It continues Firebug’s tradition of helpfully summarizing the under-the-hood details.
• I didn’t even realize Firebug supported plug-ins! What a wonderful world we live in!
• “YSlow” is a really cute name.

On the down side, like all automatic diagnostic tools, the results are a mix of really useful pointers, and really stupid “recommendations” that obviously don’t apply. For example, on my home page, YSlow recommends that I use a CDN (Content Distribution Network) to speed page delivery. For my blog? I don’t think so. And like most lint tools, there’s a way to fake it out to avoid the recommendation (I can use about:config to claim that nedbatchelder.com is a CDN), but that’s pretty silly. Better would be a way to tell YSlow to shut up about CDN’s already.

My blog gets a stinging F (56), but maybe I shouldn’t feel so bad: the YSlow page itself gets a D (67)!