Blog Posts by Marcel Duran

  • Welcome YSlow Open Source

    That's one small click for a developer, one giant leap for the performance community.

    Opensourcing YSlow on GitHub

    Please welcome YSlow into the open source world!

    YSlow was created by Yahoo! and the extensions were released to the public for free since 2007. Yahoo! has maintained the source code for the last five years, encouraged by community feedback to make improvements to the code.
    We are now publishing the source code for YSlow under the BSD Open Source license. You are encouraged to use the source code, learn how it works, fork it to make your own projects and enhance it with new rules, features, and whatever will improve this tool we all love. Since YSlow is written entirely in JavaScript, HTML and CSS, contributions are easy to do.

    The latest development version of YSlow is hosted on GitHub at If you are interested in contributing to YSlow, please fork the repo and submit pull requests. Accepted pull requests will eventually be merged back by

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  • Pushing Beyond Gzipping

    In Tony Gentilcore's chapter, "Going Beyond Gzipping," in the Even Faster Web Sites book, and at his presentation at Velocity 2009, Gentilcore describes a weird behavior where roughly 15% of visitors are not receiving compressed responses even though these user agents support compression. Although all modern browsers (circa 1998) support Gzip compression, surely 15% of users are not using browsers older than 10 years. The culprit are proxies and security software that mangle or strip the Accept-Encoding HTTP header:

    Accept-EncodXng: gzip, deflate
    X-cept-Encoding: gzip, deflate
    ---------------: -------------
    ~~~~~~~~~~~~~~~: ~~~~~~~~~~~~~


    Gentilcore emphasizes the importance of serving compressed content for these users and comes up with some approaches to workaround this issue:

    1. Appeal to the vendor of software that mangles/strips the Accept-Encoding header — but this will take some time until all users upgrade their versions.
    2. Design to
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  • Performance on Yahoo! Search for Earth Day

    Last week Yahoo! launched Earth Day campaign with a dedicated page, plus other campaign features spread across Yahoo! properties. Being the frontend engineer in charge of implementing such features for Yahoo! Search Team and a tree-hugger, I had to find a way to go green on this task. So, why not optimize it to the bone?

    The page itself is pretty light and hasn't many features besides the main search box and some tab links. So the Earth Day module would come as extra weight to the page.

    The following screenshot of the Earth Day campaign module on Yahoo! Search shows the original image. (You might be reading this after the campaign is gone or has changed).

    Earth Day Module

    Module resources

    • 9 different images (photos): JPG
    • 1 background image (green leaf): transparent PNG8
    • 1 background gradient (from white to green): PNG8

    With these image resources, I did some performance homework and strictlyfollowed the steps outlined in Even Faster Web Sites book by Stoyan Stefanov and Nicole Sulivan, to optimize

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