RefToolbar refers to a series of JavaScript/jQuery scripts that help editors add citation templates to articles. It works in conjunction with the MediaWiki extension WikiEditor. The Reftoolbar implementation is scattered across several scripts (see, for example, this, this or this prefix search). The newest version, RefToolbar 2.0 is turned on by default for new users.
Originally an opt-in Wikipedia Gadget, Reftoolbar was moved to a site-wide script on February 25, 2011, and to an opt-out gadget in April 2014.[1][2] It comes in two versions, depending on the settings at Preferences → Editing → Editor.