Fixing Cmd+Enter to Insert Newline in Hermes TUI Under Kitty

Problem

In the Hermes TUI (and other prompt_toolkit-based CLIs like Claude Code), pressing Cmd+Enter in Kitty terminal triggers Kitty’s default new_os_window action, opening a new terminal window instead of inserting a newline in the prompt.

The desired behavior: Cmd+Enter inserts a newline (same as in browser form fields), and Enter alone submits the prompt.

Root Cause

Kitty intercepts Cmd+Enter at the terminal level before it reaches the foreground application. The default mapping opens a new OS window. The application never sees the keypress.

Fix

Add one line to ~/.config/kitty/kitty.conf:

map cmd+enter send_text all \e\n

This overrides Kitty’s default and sends Escape + newline (\e\n) to the foreground process. prompt_toolkit interprets \n (0x0a) as “insert newline” in multiline mode, and submits only on \r (0x0d, carriage return – what plain Enter sends).

Verification

Tested using Kitty’s remote control API:

Launch a fresh Kitty instance with allow_remote_control yes
Run cat -v in the foreground
Send cmd+enter via kitty @ send-key cmd+enter
Confirm: foreground process receives \n, no new window created

Requirements

Kitty 0.46.1 or later
Full restart required: Cmd+Q and relaunch. Config reload (Cmd+Shift+F5) is insufficient for cmd modifier mappings.

What Does NOT Work

Attempt	Result
`disable_enhanced_keyboard_protocol all`	Kitty 0.46.1 does not recognize this option
`disable_enhanced_keyboard_protocol hermes`	Not a valid option; also, `hermes` is a python3 script so kitty sees `python3` as the process name
`map cmd+enter send_text all \r\n`	`\r\n` submits the prompt in most TUIs
`map cmd+enter combine \e \n`	`combine` merges kitty actions, not raw bytes
Config reload only (`Cmd+Shift+F5`)	`cmd` modifier mappings require full restart

Alternative: Ctrl+J

If Cmd+Enter cannot be remapped, Ctrl+J sends a literal \n (0x0a) that prompt_toolkit interprets as “insert newline.” This works without any kitty config changes.

Kitty keyboard protocol (CSI u): Enhanced keyboard protocol sends modified keys as escape sequences like [106;9u. Some TUI frameworks (prompt_toolkit) do not interpret these. If present, add map ctrl+j send_text all \n as an additional override.
Karabiner Elements: Can remap Cmd+Enter at the OS level to an unused key (e.g., F20), which Kitty then maps to \n.

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