Template:Exists

From UOGuide

A conditional template, which determines whether a page exists:

{{exists|<pagename>}} (do not use a named parameter — pagename= will not work)

If a page named "pagename" exists, the template will return the string "true". Otherwise, it will return the string "false". You can also choose your own return values: if the page exists, it will return the value of the then parameter, if present, instead of "true". If the page does not exist, it will return the value of the else parameter, if present, instead of "false".

{{exists|<pagename>|<then=>|<else=>}}

How it works: The template exploits the fact that trying to link to a non-existent page and trying to include a non-existent page as a template have the exact same effect; they produce a link to edit that page:

Therefore, the {{equal}} template is used to determine whether the string produced by linking to the page is identical to the one produced by trying to include it as a template. If they do not match, the page exists. If they do, it doesn't.