Whitespace mode is hooked into prog-mode.

init.el

@@ -412,8 +412,8 @@
 ;; Keybinding for whitespace, don't visualise newlines
 (use-package whitespace
   :config
-  (delete 'newline-mark whitespace-style)
-  (global-whitespace-mode)
+  (delete 'newline-mark whitespace-style) ; $ at eol
+  (delete 'lines whitespace-style)        ; Don't paint lines red if too long.
   ;; Don't show dots in company menu
   (defun on-off-whitespace-before-company(command)
     (when (string= "show" command)
@@ -424,6 +424,8 @@
               :before #'on-off-whitespace-before-company)
   :bind
   ("C-x w" . 'whitespace-mode)
+  :hook
+  (prog-mode . whitespace-mode)
   :custom-face
   (whitespace-space ((nil :foreground "gray18"))))
 

server/server

@@ -1,2 +1,2 @@
-127.0.0.1:51313 18545
+127.0.0.1:51313 4674
 phahw2ohVoh0oopheish7IVie9desh8aequeenei3uo8wahShe%thuadaeNa4ieh