Content-addressed URL. This allows you to link to text without:

• having to create a page first, or
• the data being lost if the site goes down.

Your text:

Example usage: footnotes, e.g. the link in "clouds can weigh a million kg[url=https://...]¹[/url]" could be a content-addressed URL with more context (like how you calculated the value, or conversions to other unit systems).

You could also use data:text/plain,... (data URL) which doesn't need a server, but this is often not parsed/clickable, or not allowed altogether. This is an alternative to data URLs, really.

Only plain text is allowed so that I hopefully don't have to police this. The size limit is a few KB. Other systems don't like URLs beyond a certain size anyway.

Source code