How to diagnose Website performance?


  • In a few circumstance, users (or website owner) found their website perform slow, and would like to identify which website component is performing slow
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In this tutorial, we will demonstrate how to use Firefox developer console to show the website responsiveness.


  1. Start a Mozilla Firefox (We prefer Firefox for simple user interface)
  2. Clear Browser cache
  3. Open Developer Console
  4. Visit the website
  5. Check the waterfall diagram, and identify which components used the most duration



Open the Browser (e.g. Mozilla Firefox), and click Ctrl-Shift-Delete to clear browser cache

Clear Browser Cache

Inside Firefox, press Ctrl-Shift-I to open Developer Console

Developer Console

Visit your website, and it will show a waterfall diagram.

Inside the diagram, it shows the time required by each website component.

Waterfall Diagram

Inside the diagram, you may click on individual website item, and check the timing.

Waterfall Diagram - Timing

Also, you may check individual website item HTTP header information (e.g. Content-Encoding, Keep-Alive, Expires)

Waterfall Diagram - Header

If you first page, e.g. index.php, performs slow, it shall to PHP or MySQL tuning.

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