Shitty

Blazingly fast. Memory-unsafe and faster than yours.

Shitty is built for low latency, fast startup, and predictable resource use. It keeps terminal state on the CPU and renders cells with native compute backends: Vulkan on Linux and Metal on macOS.

Performance

100MB catted through the GUI on an Apple-silicon MacBook, every terminal equalized first: Menlo 12pt, the same 14x28px cell, an 80x24 grid, 500 lines of scrollback. Best wall time of three runs.

Printable ASCII (the scroll path):

terminal	wall	user	throughput
shitty	0.81s	0.50s	~118 MiB/s
alacritty 0.17.0	0.96s	0.78s	~99 MiB/s
kitty 0.48.2	1.28s	0.95s	~75 MiB/s
ghostty 1.3.1	1.49s	1.60s	~64 MiB/s

Random bytes (the parser's worst case, invalid UTF-8 throughout):

terminal	wall	user	throughput
shitty	1.88s	1.79s	~51 MiB/s
alacritty 0.17.0	3.07s	2.92s	~31 MiB/s
ghostty 1.3.1	4.63s	~7.0s	~21 MiB/s
kitty 0.48.2	-	-	-

kitty sits the random payload out: it reacts to the embedded escape junk with title changes and bells instead of drawing. Reproduce with dev/compare.py, which verifies the equalized setup from inside every terminal before measuring anything.

Why

• Fast. See the tables above; dev/compare.py reproduces them.

• Correct. More than 5,000 tests, harvested from over a dozen suites - kitty, esctest, xterm's vttests, vttest, tack, libvterm, libtsm, alacritty, ghostty, contour, konsole, mosh - and driven black-box through a real PTY.

• Flicker-free. Resize frames render inside the same transaction as the bounds change; updates are damage-driven.

• Indestructible. The parser state machine is total and fuzzed with committed corpora: cat /dev/urandom is a benchmark here, not a crash report.

• Unicode done right. Cells are grapheme clusters, not codepoints: emoji sequences, variation selectors, combining marks, wide CJK.

• Self-contained. One small binary, no windowing toolkit, fonts embedded - it starts on a machine with no fonts installed at all.

• Locked down by default. Applications cannot read selections or drive the host window unless explicitly allowed.

Features

• VT52 through VT5xx controls and widely used xterm extensions.

• Primary and alternate screens, primary-screen scrollback, margins, tabs, rectangular operations, protected cells, and synchronized output.

• Reflow of primary-screen scrollback when the terminal width changes.

• Unicode grapheme clusters, combining characters, emoji sequences, and double-width characters.

• DEC single-width, double-width, and double-height lines.

• 16-colour, 256-colour, and 24-bit colour, including underline colour and extended underline styles.

• Legacy, modifyOtherKeys, and Kitty keyboard protocols.

• X10, VT200, UTF-8, SGR, SGR-pixel, and urxvt mouse protocols.

• Linear and rectangular selection, primary selection, clipboard integration, OSC 52 policy, and OSC 8 hyperlinks.

• Shell integration, notifications, progress reports, and in-band resize reporting.

• Lazy glyph rasterization, a persistent GPU glyph cache, and damage-driven compute rendering.

Shitty uses UTF-8 internally and exports TERM=xterm-256color to child processes. The host must provide the corresponding terminfo entry.

Requirements

Shitty is written in C++23 and built with Clang. The bundled libstd needs -std=c++26, which the Apple command-line-tools clang does not know: on macOS install LLVM from Homebrew and point the build at it (export CC="$(brew --prefix llvm)/bin/clang", same for CXX with clang++). Every build requires:

• Python 3, Ragel 6, and glslangValidator;

• librsvg (rsvg-convert), which renders the icon at build time;

• pkg-config;

• utf8proc 2.9 or newer;

• POSIX threads and PTY support.

The exact libstd revision used by Shitty is bundled in third_party/libstd and built as part of the same graph.

Linux additionally requires FreeType, HarfBuzz, Wayland client headers, xkbcommon, wayland-scanner, and Vulkan headers and loader. macOS requires SPIRV-Cross and uses CoreText, Cocoa, Metal, and IOSurface from the system SDK.

Brotli and simdutf are optional: Brotli only satisfies FreeType's static-link dependency chain where that applies, and simdutf 6.5 or newer accelerates Base64 over the always-available scalar implementation. Font families are resolved by CoreText on macOS and by Fontconfig (optional) on Linux; explicit font file paths work everywhere, whichever backend rasterizes them.

Linux requires a working Vulkan driver and Wayland compositor at runtime. macOS uses the native Metal driver. The native window and event-loop layer is built from third_party/plt; the terminal does not depend on a generic windowing toolkit.

The complete imported conformance suite additionally needs ncurses, Perl, and vttest.

Build

Build the default install group:

./build

Common build options:

./build -j 8
./build -B .build-debug
CPPFLAGS=-DDEBUG ./build

Run

Start the default shell:

./st

Run a command:

./st -e tmux new-session

Choose the initial terminal size and scrollback capacity:

./st -geometry 120x36 -saveLines 5000

Choose fonts:

./st -font 'DejaVu Sans Mono' -fontsize 16
./st -font 'DejaVu Sans Mono' -font 'Noto Sans Mono CJK JP'

-font accepts a family name or an explicit font file path and may be repeated: later fonts serve as fallbacks, picked per cluster by glyph coverage. Regular, bold, italic, and bold-italic faces resolve automatically. A vendored monospace-and-emoji trio is embedded in the binary as the last resort, so the terminal starts even on a system with no fonts installed at all.

Use ./st -v to print the build version without opening a window, ./st -help for the main option list, and ./st -listres for advanced terminal, colour, clipboard, and window-policy options. Boolean flags use -flag to enable and +flag to disable. SHITTY_FONT_SIZE sets the default font size; -fontsize takes precedence.

During a session, Cmd+=/Cmd+-/Cmd+0 on macOS (Ctrl+Shift+=/ Ctrl+-/Ctrl+0 on Linux) raise, lower, and restore the font size. Font resizing preserves the terminal's rows and columns by resizing the window to the new cell dimensions.

By default, applications cannot read local selections through OSC 52 and cannot manipulate or query the host window. These operations can be enabled explicitly for trusted applications.

Install

Homebrew (macOS, Apple silicon)

brew install pg83/tap/shitty

The tap tracks the latest release automatically. The same portable binary (st-darwin-arm64.tar.gz, nothing dynamically linked outside the system) is attached to every GitHub release.

Linux

The executable is named st; the desktop application and icon are named shitty:

install -Dm755 ./st /usr/local/bin/st
install -Dm644 shitty.desktop \
  /usr/local/share/applications/shitty.desktop
install -Dm644 shitty.svg \
  /usr/local/share/icons/hicolor/scalable/apps/shitty.svg

Exec=st is resolved through PATH, while Icon=shitty is resolved through the active icon theme.

Nix

A flake provides the shitty package and a development shell:

nix build           # ./result/bin/st
nix run             # run st directly
nix develop         # clang toolchain + build dependencies

Add the package to a NixOS system from the flake overlay or via:

{
  inputs.shitty.url = "github:pg83/shitty";
  # ...
  environment.systemPackages = [ inputs.shitty.packages.${system}.default ];
}

shell.nix remains available for nix-shell without flakes.

Tests

Run the full native and imported conformance suite:

./build test

Run only the native black-box suite:

./build test_suite

Run the same normal and sanitizer chains as GitHub CI:

nix build -L --no-link .#checks.x86_64-linux.build &&
  nix build -L --no-link .#checks.x86_64-linux.tests
nix build -L --no-link .#checks.x86_64-linux.build-asan &&
  nix build -L --no-link .#checks.x86_64-linux.tests-asan
nix build -L --no-link .#checks.x86_64-linux.build-ubsan &&
  nix build -L --no-link .#checks.x86_64-linux.tests-ubsan

Build an instrumented copy of the complete suite and generate LCOV, text, and browsable HTML reports:

nix build -L -o result-coverage .#checks.x86_64-linux.coverage
xdg-open result-coverage/html/index.html

The same report is attached to every GitHub coverage run and uploaded to Codecov for per-file and pull-request coverage.

The native suite drives a dedicated headless st_test binary through a real raw PTY and checks externally visible terminal snapshots and output. The production st binary does not expose the test control entry point.

Known limits

Shitty does not currently implement bidirectional text layout or inline graphics protocols such as sixel. Some historical DEC and xterm extensions are intentionally outside the supported profile.

License transition and authorship

Shitty is a hard fork and complete rewrite of Zutty. The original Zutty terminal emulator was created by Tom Szilagyi. Shitty keeps that lineage, but replaces the architecture, renderer, platform integration, testing strategy, and project identity.

Shitty is moving from the imported GPL baseline to an MIT-only codebase. It does not intend to retain the GPL as the final project license.

The source snapshot first imported into this repository, and code predating that snapshot, remains licensed under GPLv3-or-later. New Shitty contributions are dual-licensed under GPLv3-or-later and MIT. While GPL-only imported material remains in the tree, distribution of the combined work is still subject to the GPL.

See LICENSE, LICENSE.GPL3, LICENSE.MIT, and CONTRIBUTING.md for the exact terms and contribution policy.

Tom Szilagyi is the original author of Zutty, from which Shitty descends. Shitty retains his copyright notices where historical code lineage requires them; subsequent work is copyright of the Shitty contributors.