It is important that you speed up your website as much as possible because, all other factors remaining the same, a faster performing site may rank higher in Google search results. That’s because Google now considers page speed as one of the factors while ranking pages.
Google offers a free tool called Page Speed that you may use to improve the performance of your web pages. The tool performs several tests against your website and then suggests simple ways to make your site even faster.
YSlow from Yahoo! is another such tool that measures the performance of your pages and offers suggestions for improvement. Yahoo! says that the response time of web pages can be improved by 25% to 50% by following the recommendations made by the tool.
Both Page Speed and YSlow are available as add-ons for Firebug and will therefore only work if you have Google Chrome or Firefox on your computer.
If you are however running a different browser (like IE) or would like to evaluate the performance of your sites without installing add-ons, you should give GTMetrix a try.
GTMetrix will analyze your pages using both Page Speed and YSlow rules in one go and other advantage is that it runs online without requiring any add-ons.
You can setup a free account and the service will automatically run performance tests against your site at pre-defined intervals. It also preserves the reports of previous tests and you can therefore easily measure the outcome of your optimization efforts over time.
Also see: Completely Test your Website