Manual:$wgUrlProtocols

Details
Defines the protocols which are supported and translated to clickable links by the mediawiki parser. External links added to the wiki which do not begin with one of these protocols are not allowed (they are simply rendered as text and do not become links, even if enclosed in square brackets).

Some examples that don't work (because "test://" is not defined as a valid protocol):


 * test://www.example.com
 * [test://www.example.com]
 * [test://www.example.com link text]

1.6.0 and above
Since 1.6.0, the format of this setting is simply an array of allowed URI prefixes.

This default value adds three new protocols to the ones covered by the earlier 1.5.x versions:
 * telnet://
 * nntp://
 * worldwind://

1.5.x
In earlier versions the setting was a regexp expression which matched the beginning part of the URI; in other words, it is a set of prefixes separated by '|' (with '/' converted to '\/' because '/' has a special meaning in a regular expression. Note that if the string was enclosed with double quotes you would need to use "\\/", as '\' has a special meaning within double quotes.  For simplicity you should always use single quotes with this setting).

This default value causes MediaWiki to render URIs with the following prefixes as external links:
 * http://
 * https://
 * ftp://
 * irc://
 * gopher://
 * news:
 * mailto:

Older Versions
If you need this functionality in older Versions:

There is the function replaceExternalLinks in ./includes/Parser.php. Just add a line for your protocol there.