Gadget export
From Test Wiki
To export the summaryButtons gadget, click on "Download" button, save the downloaded file, go to Special:Import on the destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
*summaryButtons[ResourceLoader|hidden|type=general|dependencies=mediawiki.ui.button,mediawiki.util]|summaryButtons.css|summaryButtons.js
You must have appropriate permissions on the destination wiki (including the right to edit system messages) and import from file uploads must be enabled.