claude code: kitty keyboard protocol garbage

25 Mar, 2026 • 280 words • 2 min

Upon quitting Claude Code, pressing C-c in the terminal produces garbage like this instead of the expected ^C:

❯ 0;5u9;5u0;5uc9;5u9;5u9;5u9;5u9;5u

Something similar happens with C-a, C-e, C-l, etc. I am using zsh.

What’s happening #

Claude Code enables the kitty keyboard protocol (“CSI u mode”) for enhanced key input handling. Whenever the program exits cleanly, it restores the terminal to its original state. However, if the cleanup doesn’t fully complete (crash, SIGKILL, etc.), the terminal remains in CSI u mode.

In this mode, keypresses are sent as escape sequences rather than being interpreted by the shell. For example, Ctrl-C sends \e[99;5u (keycode 99 = c, modifier 5 = Ctrl) instead of being interpreted as SIGINT. Multiple rapid keypresses concatenate into the garbled output above.

Fix #

Reset the terminal:

reset

Or, more targeted — disable CSI u mode explicitly:

     sh
     
printf '\e[<u'

…though no one can remember this. reset is standard and simple, though it could be easily confused with clear.

Prevention #

Add a precmd hook to ~/.zshrc so the protocol is disabled before every prompt:

     zsh
     
precmd() { printf '\e[<u' 2>/dev/null }

For bash, use PROMPT_COMMAND instead:

     bash
     
PROMPT_COMMAND='printf "\e[<u" 2>/dev/null'

This is a no-op when the terminal is already in normal mode, so there’s no downside to having it always run.

This is what Claude says, but I’d rather not clutter my precmd due to Claude. For now, I am happy to run reset manually when needed.

I suspect this is well-known but they have many open bugs in their GitHub issue tracker, I couldn’t pinpoint it to a specific issue.

Update: well, someone reported it just 5 minutes ago at the time of this post.