It is with great excitement[1] that I am pleased to announce that the main LessWrong text editor[2] now has support for footnotes![3] A huge thanks to our friends over at the Effective Altruism Forum who coded this one up.
You can insert footnotes via:
1. Manually selecting text in the text box and selecting insert footnote from the footnotes menu icon.

2. Using Markdown syntax
- Type [^n] where is the number of the footnote you wish to insert.
- To insert a new footnote, use n that is <number of existing footnotes + 1>; to reuse an existing footnote, set n to be whichever footnote you are reusing.
Footnotes will automatically renumber as you add and delete them!
What's more, footnotes will render with hover-over previews once published:

That's it. Go forth and create scholarly works!
- ^
I mean it, really. I've looked forward to us adding this support for years.
- ^
That is, the LW Docs editor, as distinct from the Markdown editor and legacy Draft-JS editor.[4]
- ^
The Markdown editor already had support for footnotes using Markdown footnote syntax.
- ^
Yes, footnotes can have footnotes. And those footnotes can reference themselves.[4]
Is this feature likely to be released in the near future?
I personally have a post sitting in drafts that is far too long to rely on footnotes, as it would break the reading experience. Sidenotes would be ideal for these kinds of posts, but it would be almost as good if you had an option to put them at the end of a paragraph in a little box or something, as that would translate well to the mobile reading experience.