Both Fiddler (shown below) and Firebug can monitor Network traffic from your browser to web servers. I use it as a debugging tool all the time and could not live without it.
Discover broken links to images, java scripts, etc in your pages
Just browsing around can help you find errors. Look at the image below to see how broken links to images referred from your HTML or CSS lights up in red.
![image_thumb[9]](http://blog.fredrikhaglund.se/wp-content/uploads/2009/06/image-thumb9-thumb.png)
Strange Java Script errors – Browser does not always refresh
Have you noticed that EPiServer and other products emit a License Exception as text on your page? At least in earlier releases of EPiServer CMS it could inject it’s error message in the beginning of any file. A java script file starting with "License Exception…" does not work. Neither do a PNG or JPG file with some extra data in the beginning.
So use Fiddler when EPiServer Edit Mode does not work as expected!
- You can find that it fails to get files. This can be caused by miss configuration, like no ASP.NET wild card mapping or incorrect setup of VPP’s or siteSettings in you web.config.
- You can also see how cache directives affects your browser. The default settings in a fresh EPiServer CMS installation will tell your browser to cache the following files in 12 hours: .png .jpg .jpeg .css .js .gif.
![image_thumb[10]](http://blog.fredrikhaglund.se/wp-content/uploads/2009/06/image-thumb10-thumb.png)
So, to get rid of error messages injected in the beginning of java scripts and images hitting F5 will not help. As you see above the server returns 304 – file is not changed – and your local (broken) file is used. You need to clear your browser cache to get rid of it!
Also read more about how to configure caching in EPiServer in Per Bjurström’s blog.