There are developers on Squarespace who take full advantage of the Developer Platform and build from scratch. Then there are the more casual types (myself included) who only want to customize some CSS of a template without flipping on Dev Mode, downloading the repo, and pushing code.
Let's say you wanted to change the line height of an individual text block, or the background color of an individual page. These are usually not options on Squarespace built templates. Traditionally, the way to accomplish this would be to inspect the element of each page, and grab the Collection ID (the body ID) or the Block ID to write element specific CSS. That's a pain.
So I've written a Chrome Extension that allows you to easily see and copy the Collection ID or the Block ID of the page you're viewing so you can forget about digging through the inspector. Just turn on the extension, find the collection ID or the block ID, click the overlay button, and it's copied to your clipboard.
It should work when logged in or out. Feel free to email me if you find any bugs.