kastty

A browser-based terminal sharing tool. kastty runs a PTY on your machine, streams it to a local web UI powered by ghostty-web, and lets you view or interact with the session from your browser.

The name combines "cast" and "tty", with a nod to 「彁（ka）」— a ghost kanji that echoes the ghostty-web lineage.

Features

• Browser-based terminal -- renders a full terminal in the browser using ghostty-web
• Localhost-only -- binds to 127.0.0.1 with token-based authentication
• Replay buffer -- new connections receive recent terminal history
• Editor overlay -- open the current terminal buffer in your $EDITOR inside an in-browser overlay (Ctrl+Shift+E)
• Bundled fonts -- ships with M PLUS 1 Code and Nerd Fonts Symbols for consistent CJK and icon rendering across environments
• Font customization -- configurable terminal font family
• Tab title sync -- browser tab title follows terminal OSC title updates, with state emoji
• Single dependency runtime -- runs entirely on Bun

Install

Note

kastty supports macOS and Linux only. Windows is not supported.

Homebrew

brew install shuymn/tap/kastty

Usage

kastty [options] [-- command [args...]]

When no command is specified, kastty launches your default shell ($SHELL).

Options

Option	Default	Description
--port <n>	0 (auto)	Port to listen on
--font-family <name>	-	Terminal font family
--scrollback <lines>	50000	Requested terminal scrollback lines in browser (approximate)
--replay-buffer-bytes <n>	auto (from --scrollback)	Replay buffer size for reconnect restore
--open / --no-open	true	Auto-open browser
-h, --help	-	Show CLI help

--scrollback is applied as an internal capacity limit in ghostty-web, so the visible line count varies by output width and escape sequences.

Examples

# Start an interactive shell session
kastty

# Run a specific command with a custom font
kastty --font-family "Fira Code" -- htop

# Pass flags to the target command
kastty -- htop -d 10

# Increase local scrollback and reconnect replay history
kastty --scrollback 200000 --replay-buffer-bytes 33554432

# Start without opening the browser
kastty --no-open

Editor overlay

Press Ctrl+Shift+E to open the current terminal buffer in your editor. kastty snapshots the visible buffer and scrollback, writes it to a temporary file, and runs your editor in a dedicated PTY rendered as an overlay above the terminal. The main session keeps running untouched underneath.

• The editor command is taken from $VISUAL, falling back to $EDITOR. Arguments are honored, e.g. EDITOR="nvim -R". If neither is set, kastty shows an error and does not open the overlay.
• While the overlay is focused, keystrokes go to the editor, not the main terminal.
• Exiting the editor closes the overlay, removes the temporary file, and returns focus to the main terminal.
• Only one overlay can be open at a time; pressing the shortcut again while it is open shows a notice instead of opening a second one.

# Use a specific editor for the overlay
EDITOR=nvim kastty

Note

The buffer text is captured as plain text; ANSI colors and styling are not preserved. The shortcut is fixed to Ctrl+Shift+E (chosen to avoid clashing with browser copy/paste).

Contributing

Requirements

• Bun

Setup

bun install

Build

Build a single executable:

bun run build

This produces a kastty binary in the project root.

Development

# Lint
bun run lint

# Format
bun run fmt

# Type check
bun run typecheck

# Run tests
bun test

# All checks
bun run check

License

MIT