Yahoo has changed the licence on the YSlow performance analysis tool to a BSD licence and published the entire code base on Github. YSlow allows web developers to check their pages for best practices that are designed to ensure that a web site operates at optimum speed. Yahoo encourages developers to work on the code – comprising JavaScript, HTML and CSS – and begin fixing bugs and enhancing YSlow.

Previously, developers outside Yahoo were only able to indirectly influence the development of the tool by providing feedback in Yahoo's Exceptional Performance group. Now that the source code has been released, they can contribute directly, and the YSlow project can be easily forked on Github. Yahoo plans to continue to maintain the stable branch and a development branch, both maintained by YSlow project lead Marcel Duran. Developers are encouraged to fork the development branch, as pull requests on modifications to the stable branch will not be accepted back. Pull requests from the community that are accepted will then be integrated into this version and into the tool's existing browser extensions.

YSlow has been maintained by Yahoo since 2007 and the product's core components have been available under the Mozilla Public Licence 1.1 (MPL) since then. Developers can install the tool using extensions which are available for Firefox, Chrome, Safari and Opera. There is also a bookmarklet for mobile devices and a recently introduced command line version. YSlow is based on development work by Steve Souders, who developed 13 performance best practices for Yahoo. Souders later moved to Google, where he has continued to work on other web performance tools.

(djwm)