What is a User Agent?
A user agent is an application/software that connects to your web server and requests pages and files of your website. A user agent can be a browser like Internet Explorer or FireFox, can be a robot crawling and indexing the web for a search engine, can be an online service, etc...
User Agents identify themselves with a "User Agent String" that they send to the server when they make a request. like
"Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 GTB6" (FireFox)
"Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; InfoPath.2)" (Internet Explorer)
"Yandex/1.01.001 (compatible; Win16; I)" (Yandex search engine robot)
etc...
As you can see each user agent string contains lots of information like the platform, version, rendering engine, ... so each user agent may use lots of different user agent strings to identify itself based on it's version, the platform is it running on, etc...
How does TraceWatch identify User Agents?
TraceWatch has a list of user agents. Each user agent in the list has a user agent string pattern.
When a new user agent string is encountered it is tested against each user agent's pattern in the list from top to bottom until a match is found.
You can view and manipulate this list of user agents in Administrate > User Agents page.
User Agents Administration Page
This is the page where you can view and change TraceWatch's list of user agents
![[user agents page screenshot]](/contents/doc/advanced/user_agents/screenshot.gif)
Adding a new user agent
In the new user agent box, enter a name for the user agent, enter the user agent string pattern in the pattern box and click "Add User Agent" button.
The pattern must be a valid php regular expression (perl compatible). There are various resources on the net to make you familliar with regular expressions.
After adding the user agent you can test your pattern by using the Test Bar. Enter some different user agent strings in the box to see which ones match your pattern.
[NOTE] Be carefull about the pattern. Make sure it only matches the intended user agent and doesn't accidentally match strings belonging to user agents below it in the list.
[NOTE] Just adding a user agent here doesn't make visitors with that user agent identified as robots. If you are adding a robot user agent you should also go to Administrate > Visitor Types and add this user agent as "Robot Visitor Type" identifier.
