Interface administrators are users with the ability to edit sitewide CSS/JS pages (pages such as MediaWiki:Common.js or MediaWiki:Vector.css, or the gadget pages listed on Special:Gadgets). These pages are executed by the browser of wiki editors and readers as code, which can be used to change how content is styled, change the behavior of pages, or even create highly complex tools such as wikEd (they can also edit all other pages in the MediaWiki namespace).
Editing CSS/JS that gets executed in other users' browsers is a very powerful and potentially dangerous in the hands of a malicious user; interface administrators should be users who are highly trusted, have at least a basic understanding of CSS and JS, are aware of the privacy expectations of Wikimedia wikis, and have a decent understanding of account security (choosing strong unique passwords, not getting infected by malware, preferably using Two-factor authentication).
Request for interface adminship
Interface adminship can be granted and removed by bureaucrats. Users may request interface adminship at Wikidata:Requests for permissions/Interface administrator. The vote will last for 7 days; 75% support and 8 support votes are required.
Users with staff accounts can add or remove the flag from their own account.
As a transitional rule, any administrators elected before August 27, 2018 (and who have not lost adminship before requesting interface adminship) may get interface adminship speedily before February 27, 2019.
Given the sensitivity of the flag, any users with zero edits or log action in six months, or zero JS/CSS edits outside their user space in twelve months, may have their interface administrator flag removed. They may reapply in the usual way described above.
Interface administrators are expected to reply promptly and civilly to concerns about their interface administrator actions. Repeated failure to do so may result in removal of the right, subject to the usual procedures.