"TemplateSandbox" lets you preview a page with a change in a template it uses. At the bottom of the edit form in the Template and Module namespaces, a new box will appear that allows you to preview other pages as they would appear if you saved the template/module you are currently editing. Example: try editing the sample "thank-you" template https://www.mediawiki.org/wiki/Template:Thankyou . On the edit form, under the Save button, you'll see "Preview page with this template" -- try User_talk:Example_user . Or, go to https://www.mediawiki.org/wiki/Special:TemplateSandbox and give it the "sandbox prefix" User:Sharihareswara (WMF)/sandbox and tell it to "render page" User_talk:Example_user . You'll see the ugly changes I made to the template in my sandbox. More information at https://en.wikipedia.org/wiki/Wikipedia:VPT#New_feature_needs_testing . You can check this out in the new version of MediaWiki, now live on mediawiki.org, but until we have more feedback and improvements we aren't pushing it live on the other sites. We figure this will make it easier for people to hack on templates, and to develop new Lua templates to replace wikitext templates. -- Sumana Harihareswara Engineering Community Manager Wikimedia Foundation