This week, Anthropic accidentally leaked a whole bunch of information about Claude Code. In addition to revealing many of their future plans, the leak showed that the tool uses some rudimentary pattern-matching to detect user frustration.

Claude Code is actively watching our chat messages for words and phrases—including f-bombs and other curses—that serve as signs of user frustration.

The exact regex pattern is a delight to read:

/\b(wtf|wth|ffs|omfg|shit(ty|tiest)?|dumbass|horrible|awful| piss(ed|ing)? off|piece of (shit|crap|junk)|what the (fuck|hell)| fucking? (broken|useless|terrible|awful|horrible)|fuck you| screw (this|you)|so frustrating|this sucks|damn it)\b/

It’s very simple and surely very effective.