If you install: http://www.mediawiki.org/wiki/Extension:VariablesExtension#Installation Then edit the main page to contain the following (between the '---'): --- {{#vardefine:pi|3.14159265418}} {{#expr:{{#var:pi}}+1}} --- The main page should, when rendered, now, show the number 4.14159265418 What I would like is something very similar called "CellsExtension" which provides only the keyword "#cell" as in: --- {{#expr:{{#cell:pi}}+1}} --- However, it gets the value of "pi" from: http://somedomain.org/mediawiki/index.php?title=Pi Ideally, whenever a mediawiki rendered page is cached, dependency pointers are created from all pages from which cells fetched values during rendering of the page (implying the evaluation of #expr's. That way, when the mediawiki source for one of the cached pages is edited, not only is its cached rendering deleted, but so are all cached renderings that depend on it directly or indirectly. This is so that the next time those pages are accessed, they are rendered -- and cached -- again, freshly evaluating the formulas in the #expr's (which, of course, will contain #cell references such as {{#cell:pi}}).