I present to your attention a user script for Greasemonkey, Tampermonkey and others.
The script adds the "Count symbols" button next to the "Post" and "Preview" buttons.
When you click this button, the script performs the following actions:
1. Takes everything from the "Reply" field.
2. Removes all citations and defines only your message.
3. Removes extra spaces.
4. Counts and displays count symbols in your message
With Whitespaces.
5. Counts and displays count symbols in your message
Without whitespaces.
Example:
GitHub:
https://github.com/DimNS/UserScriptsOpenUserJS:
https://openuserjs.org/scripts/DimNS/Bitcointalk_Message_Symbols_Count