# Using about.html to debug infocenters

When developing an infocenter sometimes not all of the books show as expected or customizations do not have the desired effect. The about.html page can be used to get information about installed plug-ins and help system preferences. If the home page of the help system is

    http://<hostname>:<port>/help/index.jsp

the about page has a url of

    http://<hostname>:<port>/help/about.html

Without any parameters the about page shows a list of all plug-ins installed on the system. Parameters can be added to show other kinds of information as follows:

- `about.html?show=preferences` shows the values of the help system preferences.
- `about.html?show=agent` shows the user agent information from the Web Browser used to read the page.