The tool is dormant at http://tools.wmflabs.org/magnus-toolserver/coord_gen.php with @Magnus offering to prioritize resurrecting it (cf. http://tools.wmflabs.org/magnus-toolserver/), but I think that conceptually this would be (much) better done as a button in the edit toolbar where you could enter coordinates in a OOjs UI dialog box or paste a link from Google Maps that gets dissected, etc., etc., etc. (That might even be a suitable project for Google Code-In & Co.)