YSlow – a nice performance plugin to Firebug

I’m sure you follow web standards, write semantic HTML and separate content (HTML) from presentation (CSS) and interaction (JavaScript). It’s all accessible and lean at the same time. So, what’s the next step. Performance, I tell you!

You can write good code but still it’s a bit slow for the end user, it takes time to download, it’s seems to be a delay before the visual presentation is there etc. To me, the next item on the list is to start to look at performance issues and best practices how to avoid them.

To assist you with this work, I’d like to recommend the YSlow plugin from Yahoo!, which becomes a part of the outstanding Firebug add-on to Firefox. It analyzes your code and gives you pointers how to improve performance and avoid common pitfalls. Some of them are about how to structure your interface code, while others are more focused on server settings.

Some advice should be taken with a grain of salt, given a number of criteria, context and so forth, and you need to be aware that advice that would indeed help a high-traffic web site such as Yahoo!’s might not apply to your web site. This is covered in detail in the excellent article YSlow: Yahoo’s Problems Are Not Your Problems.

Overall, though, it is a great tool to easily distinguish some code implementations which can be tweaked in a short moment to get a better performance, and help you find minor things that are way to easy to overlook while developing. The items it points out give you suggestions how to make improvements and you should read the YSlow User Guide to get started.

Read more about performance improvements

If you think this is an interesting topic, I highly recommend two articles at Vitamin that discuss how to improve performance, but also what eventual problems you might run into when doing it.


  • […] Check it out! While looking through the blogosphere we stumbled on an interesting post today.Here’s a quick excerptI’m sure you follow web standards, write semantic HTML and separate content from presentation and interaction . […]

  • Andreas says:

    I saw Nate Koechley's talk about this at @media 2007. Really interesting and I went home and started implementing the changes on my site. YSlow is really cool and I love that it actually gives you a score you can compare with mates =) I think the biggest improvement for me was definitely minifying and merging javascript as well as including all JS att the bottom of the page. Minification and merging is taken care of "on the fly" thanks to the PHP-port of Dead Edwards JS-packer. Works really well actually.

  • Indeed a great plugin (it's been around for a while though πŸ˜‰ ) We managed to get our CMS from a D to an A by optimising our css and javascript, and we really sped it all up.

    It might be nice to note, that YSlow's criteria are arranged in a way that the top most advices will have the biggest impact on your speed. (According to Steve Souders talk at FOWA last october)

  • Robert Nyman says:


    Good to see that you like it!


    Yes, performance should never be underrated.

    Interesting about the order, if that's correct!

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