For years Yahoo’s application YSlow has been a staple in the Web developer’s toolkit since 2007. Now the company has released the code on Github under the BSD license. The apps is entirely built in JavaScript, HTML and CSS.

YSlow is available from the command line or as a browser plugin for Firefox, Chrome, Safari, Opera or as a bookmarketlet, and gives front-end developers feedback as to how quickly a site loads and what may be slowing it down. Here’s the basic feature list:

• Grades web page based on one of three predefined ruleset or a user-defined ruleset;
• It offers suggestions for improving the page’s performance;
• Summarizes the page’s components;
• Displays statistics about the page;
• Provides tools for performance analysis, including Smush.it™ and JSLint.

Google offers its own similar tool called PageSpeed, which also works in the browser with no plugin required. And tools like New Relic also offer insight into site speed and performance.