Thursday, December 6th, 2007

YSlow 0.9 Release: Grokking XHR and more

Category: Performance, Utility, Yahoo!

Steve Souders and Stoyan Stefanov have released YSlow 0.9:

There are two big features in this release. By integrating more tightly with Firebug’s Net Panel, YSlow now finds non-DOM components such as Ajax requests and image beacons. And YSlow now crawls frames and iframes and analyzes those resources as well. There are several other new features and bug fixes described in the release notes including highlighting 404s, better detection of CSS expressions and JavaScript minification, and searching within the YSlow panel.

These features make YSlow stronger at identifying performance improvements for Web 2.0 applications. It’s great that YSlow does even better performance analysis of pages, but be forewarned that your previous YSlow scores will drop if these new-found components exhibit bad performance characteristics. As mentioned in Rule 14 – Make Ajax Cacheable, some of the performance improvements that are readily applied to static content (far future Expires header, gzip compression, minification) can also be applied to Ajax responses. Whether it’s Web 1.0 or Web 2.0, YSlow 0.9 helps you figure out what to fix to make your pages faster for your users.

Stoyan Stefanov goes into more detail on the new features, and you can check out the release notes.

Posted by Dion Almaer at 12:08 am

3.8 rating from 17 votes


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Such a good news!

Comment by blankyao — December 6, 2007

So, what does the coder tab do? It’s not in YSlow and it’s not in Firebug… Another extension?

Comment by Alantin — December 6, 2007

can somebody light me on one question? does it only analyzes pages using YUI library, or any page will work? such as prototype/jquery/dojo etc?

Comment by Anonymous — December 6, 2007

It analyzes all pages regardless of library (even if it has none).

This is great to hear. Just grabbed thde update!

Comment by Site Smart — December 6, 2007

Ditto on the Coder tab question. Anyone know where it’s coming from? Can Stoyan share with us?

Comment by Paul Irish — December 6, 2007

The Coder tab is another extension by Steve Souders:

I use it all the time when working on YSlow, it allows you to alter any property/method inside Firefox’s chrome window on the fly, without the need to restart Firefox.

Comment by Stoyan — December 6, 2007

LiveCoder ( is very cool. Joe Hewitt came to do a talk at Yahoo! and mentioned how hard it was to build Firebug because there’s no Firebug for building Firefox addons. That night I built LiveCoder (and unfortunately it hasn’t had much more attention beyond that one night). LiveCoder let’s you examine and modify the Firefox chrome (including all aspects of Firebug). So if you’re building an addon you can find bugs and test your fixes without having to rebuild and reload your addon. There’s one feature that makes it valuable for normal web pages – you can modify function definitions on-the-fly (a feature that would be nice to add to Firebug). I’ll spruce up the web page to give some intriguing examples. I use LiveCoder every day, so you might find it useful, too.

Comment by souders — December 6, 2007

…impossible to imagine life before FireBug… YSlow is useful — keep up the awesome work and many thanks, guys!

Comment by Mark Holton — December 6, 2007

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