How to speed up your website with Yslow

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Photo by Ezu

One of the downsides of the increase in widgets and customization over the last few years is that they often result in a web page that takes seconds to load. Thanks to my desktop app heritage, I’m really sensitive to this, since poor responsiveness in an application destroys the user experience. The emotional response to waiting is frustration, and both gives users a subconscious motivation to avoid it and a chance to get distracted by something else and abandon your service.

That’s made me very wary of installing new widgets on this blog, since I sometimes see long loading times even now, and I’ve never quite been sure why. I wanted a new discussion service though, and Intense Debate looked very appealing, so I resolved to install it and also figure out how to profile my site.

Firebug is the best tool for getting under the hood and understanding what Firefox is up to when you load a page, but it’s more aimed at debugging script, CSS and markup problems rather than understanding performance issues. That’s where Yslow, a free plugin for Firebug from Yahoo, comes in.

It’s based on some principles of website optimization that Yahoo have worked out. It applies these rules programatically to your page and then gives you a report card giving details of problems in each are. My site received an F. There’s a whole lot of improvements I’ll be looking at implementing, but one that’s interesting is setting a long expiry time for external objects like scripts and images. This is inconvenient when you change a resource on the server, since you also need to change the name, but Yahoo estimate that 80% of fetches can be avoided in a typical scenario if you set an expiry header that allows the browser to cache the resource locally. I’ll be poking some of my widget providers to see if that’s possible.

I highly recommend giving Yslow a shot on your site, you’ll learn a lot about what your page loads actually involve, and probably get some ideas on improving performance.

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