Since web development is a relatively new discipline, many important tools known from conventional development are hardly available. Debugging web servers and web application is usually a complicated task if you don't want to go back to using a network sniffer like ngrep. LiveHTTPHeaders aims to bridge this gap by providing a debugger for HTTP header data.
LiveHTTPHeaders is an extension to Mozilla browsers. This means that when debugging you use your browser in the usual way while the extensions prints out the HTTP header data resulting from your actions. You can choose to run LiveHTTPHeaders in a separate window, the sidebar or in a tab. Using the sidebar lets you only view the headers but take no further actions. Running LiveHTTPHeaders inside a tab has the minor drawback that switching tabs with CTRL+TAB won't work because it is used for navigation inside the LiveHTTPHeaders window. So the best choice is to launch it in a separate window.
showing request and response headers
When making a request to a web server LiveHTTPHeaders prints out both the HTTP headers from the request and from the response of the server. This makes it easy to track redirects and debug other potential causes of problems. It also shows some information about web servers that is traditionally unavailable, like the server software and version.
Another interesting feature is the modification of requests. You can modify the User-Agent string, language settings or the contents of POST requests. Unfortunately there is no way to change the IP address to which an request is sent. This makes it impossible to test a web application moving to a new server prior to the final switch in the DNS configuration.
HTTP header logs may be saved into a file for later analysis or replay. If the amount of data produced by LiveHTTPHeaders is too large you can create a blacklist or a whitelist based on regular expressions. If you are only interested in the request URLs you can use the generator dialog to save only them. A help window assists in finding out the correct options.
To sum it up, LiveHTTPHeaders is a very useful tool both for web developers and web server administrators. When using it, tracking down the source of a problem is often a quick and easy job.