emacs-winum/README.md

window-numbering

Numbered window shortcuts for Emacs

Enable window-numbering-mode and use M-1 through M-0 to navigate.

If you want to affect the numbers, use window-numbering-before-hook or window-numbering-assign-func. For instance, to always assign the calculator window the number 9, add the following to your .emacs:

(setq window-numbering-assign-func
      (lambda () (when (equal (buffer-name) "*Calculator*") 9)))