How the link keeps your list private
Give your list a title and, if you like, a note for givers. Add each item with details that help someone choose (size, colour, "secondhand is fine") and a rough price. How much you want it sorts items into Would love most, Would like and Small idea, so people can see what matters.
The share link updates as you type. Copy it into a message or a card; whoever opens it sees the finished list, ready to copy or print.
Everything you write is packed into the part of the link after the # sign, called the fragment. As MDN's guide to URI fragments puts it, the fragment is not sent to the server when the page is requested (see also RFC 3986, section 3.5). So the list never reaches this site: it travels only inside the link you send. Your draft is also kept in this browser's local storage so you can come back to it.
Long lists make long links. Past about 2,000 characters some apps may cut a link short, so keep details brief.