How deep do you know how your website performed? Your website loading time is one of the key factors that will attract your visitors to stay longer in your website . Luckily there is Yahoo YSlow that can give us answer about that.

Installation
This is Firefox add on which can be installed easily from Yahoo YSlow website, but you must have Firebug installed prior that. Installation process is straight forward and it can used it right away

How to use it?
Click small speedometer at the bottom of your Firefox browser. It will divide you screen to 2 part where there the bottom one would be your Yahoo YSlow menu. Click Performance, Stats, or Components to have YSlow analyze your page.

Perfomance. - You will see how your website page is measured and graded (with point) It describes each metric briefly and the best practice to optimize you website

Stats - Your cache

component - list down all files such as javascript, CSS,doc, image and etc

Print your report
This is very useful especially if you want to view the report off line. From Tool -> Printable View, you will be able to view the whole report in 1 page

More info
Read their FAQ and help pages for more information

How to get accurate result?
Please clear your browser cache before running YSlow. Why?

Performance Grade
This is the grade some of major websites that I have tested using this tool

Google : A (99)
Yahoo : get A (90)
Dell: D (66
Ebay D (69)