VisualEditor Citation Needed (VECN) is a user script which adds a button (under "Insert") in VisualEditor to add a citation needed tag.

Installation instructions

Hint: It's much easier if you get ScriptInstaller, then navigate to User:Tol/VECN.js and click "Install" at the top.

However, here's the manual method:

1. Place {{ subst:iusc|User:Tol/VECN.js}} on Special:MyPage/common.js or a skin-specific page, like Special:MyPage/vector.js.
2. Clear your cache and enjoy!