YSlow data is garbage

I had been made aware of the Firefox plugin a few months ago by a high profile customer who was worrying about his site’s performance. At the time I dismissed most of what it was reporting as garbage.

I had yet to install it or try it on my own site… I did today. It randomly grades this site C or D; Microsoft got an ugly D; Yahoo! Finance got a C; Yahoo itself fetched a B. The only site I’ve found that got an A was Google’s.

I was quite surprised. Then again, taking a closer look at what it’s complaining about:

  • Use a CDN: on a site powered by WordPress? Yeah, right. And place assets on a separate domain name to avoid cookie overhead, I would assume? For a site like CNN, that makes sense. But for my own minuscule site, that seems so overkill…
  • Add expires headers long in the future: valid point, unless I decide to change the images. I’ll cope with the 304 requests for now, but I’ll probably revisit the idea.
  • Configure Etags: amusingly, all of the files it reports as having none actually have one, and they’re returning a 304 Not Modified header. I’m assuming this is a bug in YSlow, whereby it doesn’t check whether the file is in the cache.
  • Add gzip compression: the same bug, in all likelihood, since the files are actually gzipped when they’re sent to the browser.
  • Reduce the number of DOM elements: while correct in theory, that possibly is the silliest thing I’ve read this year… How is a site supposed to be customizable without some amount of DOM?
  • Place background images in sprites: as if… that works in some cases, but definitely not all of them. In particular when you need to center-align an icon with text whose size can vary.

YSlow was garbage when it was released. It still is; and it’s full of bugs.

The most horrible thing, though, is that this thing is going to become some kind of a benchmark for worried users who don’t know any better in the year to come, courtesy of Google’s new indexing algorithm…


Comments on YSlow data is garbage Leave a Comment

  1. I would agree that a lot of data from YSlow is garbage. Recently tried the service and did find a few things wrong with a site I was diagnosing, mostly common sense stuff that I had to be reminded of. But the CDN request for a site running on Wordpress also made me go “hmmm?”

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