Since hotkeys don't seem to be documented anywhere, here's a list of the ones I know. This is a WIP. I'll be adding to it as I remember/find more. Contributions are very welcome.

I presume hotkeys may work or not depending on the browser (I'm on Brave), and some keys may also be different on keyboard layouts from different countries (usually the symbol keys). One example is the comment/uncomment key. I'll list what I know from my keyboard, followed by any alternatives I know of in parentheses.

@HomineLudens pointed out on Discord that "the editor is based on Ace", so some or many of its hotkeys are the same. I'll be copying them here as I can.

(LMB, MMB and RMB are the Left, Middle and Right mouse buttons)

The list:

• code editor

  • Misc

    • F1 - pops up a menu with actions (and hotkeys) (make sure code editor is focused)
    • F2 - toggle fold widget (not sure what that means, I pressed it and it folded the code-block around my cursor)
    • ctrl , - show text editor settings
    • ctrl Z - undo
    • ctrl Y (ctrl shift Z) - redo
    • ctrl F - find (make sure the code editor is focused, or the browser's finder will pop up instead)
    • ctrl H - find & replace
    • ctrl C - copy
    • ctrl X - cut
    • ctrl V - paste
    • ctrl ~ (ctrl /) - comment/uncomment line
    • ctrl shift ~ (ctrl shift /) - block comment/uncomment
    • ctrl up/down - scroll text up/down
    • ctrl shift up/down - cycle numbers under cursor, or certain words (get* <-> set*, maybe others) under cursor
    • alt E - go to next error
    • alt shift E - go to previous error

  • Line

    • ctrl L - go to line
    • ctrl shift D - duplicate line downward
    • alt shift up/down - duplicate line up-/downward
    • alt up/down - move line up/down (doesn't work for me because one of my browser extensions uses it)
    • ctrl D - delete line

  • Multicursors

    • ctrl alt up/down - add a cursor to the line above/below
    • ctrl LMB - add a cursor to the clicked line
    • ctrl K - select next occurrence of the selected text (or of the last one selected in this way, if nothing is selected)
    • ctrl shift K - select previous occurrence of the selected text (or of the last one selected in this way, if nothing is selected)
    • ctrl alt K - select all occurrences of the selected text
    • ctrl alt left/right - add previous/next occurrence of the selected text to the selection

• sprite editor

  • Misc

    • ctrl Z - undo
    • ctrl Y (ctrl shift Z) - redo
    • ctrl C - copy selection, or entire sprite if no selection
    • ctrl X - cut selection, or entire sprite if no selection
    • ctrl V - paste
    • space LMB - pan view
    • scroll wheel - zoom view
    • LMB(MMB) - use selected tool
    • RMB - quick eraser
    • alt - quick color picker

  • Selection tool

    • LBM drag - move selection
    • shift LMB drag - drag the selected pixels
    • alt LMB drag - drag a copy of the selected pixels

I think it should be added to the documentation :)