kitty - A terminal emulator

Major Features

• Uses OpenGL for rendering, offloads rendering to the GPU for lower system load and buttery smooth scrolling. Uses threaded rendering to minimize input latency.

• Supports all modern terminal features: graphics (images), unicode, true-color, OpenType ligatures, mouse protocol, focus tracking, bracketed paste and so on.

• Supports tiling multiple terminal windows side by side in different layouts without needing to use an extra program like tmux

• Can be controlled from scripts or the shell prompt, even over SSH.

• Has a framework for kittens, small terminal programs that can be used to extend kitty’s functionality. For example, they are used for Unicode input and URL hints.

• Supports startup sessions which allow you to specify the window/tab layout, working directories and programs to run on startup.

• Cross-platform support: kitty currently works on Linux and macOS, but because it uses only OpenGL for rendering, it should be trivial to port to other platforms.

• Allows you to open the scrollback buffer in a separate window using arbitrary programs of your choice. This is useful for browsing the history comfortably in a pager or editor.

Table of Contents

• Major Features
• Installation
  • Dependencies
  • Install and run from source
  • Linux packages
  • macOS packages
• Design philosophy
• Tabs and Windows
  • Scrolling
  • Tabs
  • Windows
  • Miscellaneous
• Controlling kitty from scripts
• The scrollback buffer
• Unicode input
• URL hints
• Miscellaneous features
• Layouts
• Configuration
• Startup Sessions
• Protocol Extensions
• Font control
• Performance
• Note for Linux/macOS packagers
• Frequently Asked Questions
  • Some special symbols are rendered small/truncated in kitty?
  • How do I build kitty.app on macOS?
  • Using a color theme with a background color does not work well in vim?
  • I get errors about the terminal being unknown or opening the terminal failing when SSHing into a different computer?
• Resources on terminal behavior

Installation

kitty is designed to run from source, for easy hackability. Make sure the following dependencies are installed first.

Dependencies

• python >= 3.5

• harfbuzz >= 1.5.0

• zlib

• libpng

• freetype (not needed on macOS)

• fontconfig (not needed on macOS)

• ImageMagick (optional, needed to use the kitty icat tool to display images in the terminal)

• gcc or clang (required only for building)

• pkg-config (required only for building)

• For building on Linux in addition to the above dependencies you might also need to install the -dev packages for xcursor, xrandr, xinerama, libgl1-mesa and xkbcommon-x11, if they are not already installed by your distro.

Install and run from source

git clone https://github.com/kovidgoyal/kitty && cd kitty

Now build the C parts of kitty with the following command:

make

You can run kitty, as:

python3 .

Linux packages

• Arch Linux: AUR git package https://aur.archlinux.org/packages/kitty-git/

• Arch Linux: AUR stable package https://aur.archlinux.org/packages/kitty/

• NixOS / nixpkgs: https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/kitty/default.nix

• Gentoo: https://packages.gentoo.org/packages/x11-terms/kitty

macOS packages

kitty is available as a macOS dmg file for easy installation from the releases page. You can also run kitty directly from source using the above install from source instructions, after installing its dependencies using brew or a similar package manager.

Design philosophy

kitty is designed for power keyboard users. To that end all its controls work with the keyboard (although it fully supports mouse interactions as well). Its configuration is a simple, human editable, single file for easy reproducibility (I like to store config files in source control).

The code in kitty is designed to be simple, modular and hackable. It is written in a mix of C (for performance sensitive parts) and Python (for easy hackability of the UI). It does not depend on any large and complex UI toolkit, using only OpenGL for rendering everything.

Finally, kitty is designed from the ground up to support all modern terminal features, such as unicode, true color, bold/italic fonts, text formatting, etc. It even extends existing text formatting escape codes, to add support for features not available elsewhere, such as colored and styled (curly) underlines. One of the design goals of kitty is to be easily extensible so that new features can be added in the future with relatively less effort.

Tabs and Windows

kitty is capable of running multiple programs organized into tabs and windows. The top level of organization is the Tab. Each tab consists of one or more windows. The windows can be arranged in multiple different layouts, like windows are organized in a tiling window manager. The keyboard controls (which are all customizable) for tabs and windows are:

Scrolling

Action	Shortcut
Scroll line up	ctrl+shift+up or ctrl+shift+k
Scroll line down	ctrl+shift+down or ctrl+shift+j
Scroll page up	ctrl+shift+page_up
Scroll page down	ctrl+shift+page_down
Scroll to top	ctrl+shift+home
Scroll to bottom	ctrl+shift+end

Tabs

Action	Shortcut
New tab	ctrl+shift+t
Close tab	ctrl+shift+q
Next tab	ctrl+shift+right
Previous tab	ctrl+shift+left
Next layout	ctrl+shift+l
Move tab forward	ctrl+shift+.
Move tab backward	ctrl+shift+,

Windows

Action	Shortcut
New window	ctrl+shift+enter
New OS window	ctrl+shift+n
Close window	ctrl+shift+w
Next window	ctrl+shift+]
Previous window	ctrl+shift+[
Move window forward	ctrl+shift+f
Move window backward	ctrl+shift+b
Move window to top	ctrl+shift+`
Focus specific window (windows are counted clockwise from the top left corner)	ctrl+shift+1, ctrl+shift+2 …​ ctrl+shift+0

Miscellaneous

Action	Shortcut
Increase font size	ctrl+shift+equal
Decrease font size	ctrl+shift+minus
Restore font size	ctrl+shift+backspace
Toggle fullscreen	ctrl+shift+f11
Input unicode character	ctrl+shift+u
Click URL using the keyboard	ctrl+shift+e
Pass current selection to program	ctrl+shift+o
Edit kitty config file	ctrl+shift+f2

Controlling kitty from scripts

You can control kitty from the command line/scripts by sending it messages. You can tell kitty to open/close/rename tabs and windows. You can even send arbitrary input/text to any specified window. Messages can be sent using kitty @. Note that you must set allow_remote_control yes in your kitty.conf to use this feature. It even works over SSH connections. This feature is best illustrated with a tutorial.

The scrollback buffer

kitty supports scrolling back to view history, just like most terminals. You can use either the keyboard shortcuts or the mouse scroll wheel to do so. However, kitty has an extra, neat feature. Sometimes you need to explore the scrollback buffer in more detail, maybe search for some text or refer to it side-by-side while typing in a follow-up command. kitty allows you to do this by pressing the ctrl+shift+h key-combination, which will open the scrollback buffer in your favorite pager program (which is less by default). Colors and text formatting are preserved. You can explore the scrollback pager comfortably within the pager.

Unicode input

You can input unicode characters by name, hex code, recently used and even an editable favorites list. Press ctrl+shift+u to start the unicode input widget, shown below.

In Code mode, you enter a unicode character by typing in the hex code for the character and pressing enter, for example, type in 2716 and press enter to get ✖. You can also choose a character from the list of recently used characters by typing a leading period and then the two character index and pressing Enter.

In Name mode you instead type words from the character name and use the arrow keys/tab to select the character from the displayed matches. You can also type a leading period and the index for the match if you dont like to use arrow keys.

URL hints

kitty has a hints mode to click URLs visible on the screen by using only the keyboard. Press ctrl+shift+e to activate hints mode, as shown below.

Miscellaneous features

You can double click to select a word and triple click to select a line. You can also hold down ctrl+shift and click on a URL to open it in a browser.

Layouts

Currently, there are five layouts available,

• Stack — Only a single maximized window is shown at a time

• Tall — One window is shown full height on the left, the rest of the windows are shown one below the other on the right

• Grid — All windows are shown in a grid

• Horizontal — All windows are shown side-by-side

• Vertical — All windows are shown one below the other

You can switch between layouts using the ctrl+shift+l key combination. You can also create shortcuts to select particular layouts, and choose which layouts you want to enable/disable, see kitty.conf for examples.

Writing a new layout only requires about fifty lines of code, so if there is some layout you want, take a look at layout.py and submit a pull request!

Configuration

kitty is highly customizable, everything from keyboard shortcuts, to painting frames-per-second. See the heavily commented default config file. By default kitty looks for a config file in the OS config directory (usually ~/.config/kitty/kitty.conf on Linux and ~/Library/Preferences/kitty/kitty.conf on macOS) but you can pass a specific path via the --config option.

Startup Sessions

You can control the tabs, window layout, working directory, startup programs, etc. by creating a "session" file and using the --session command line flag. For example:

# Set the window layout for the current tab
layout tall
# Set the working directory for windows in the current tab
cd ~
# Create a window and run the specified command in it
launch zsh
launch vim
# Set the title for the next window
title Chat with x
launch irssi --profile x

# Create a new tab (the part after new_tab is the optional tab name which will
# be displayed in the tab bar, if omitted, the title of the active window will
# be used instead)
new_tab my tab
cd ~/somewhere
# Set the layouts allowed in this tab
enabled_layouts tall, stack
# Set the current layout
layout stack
launch zsh
# Make the current window the active (focused) window
focus
launch emacs

Protocol Extensions

kitty has a few extensions to the xterm protocol, to enable advanced features, see Protocol Extensions.

Font control

kitty has extremely flexible and powerful font selection features. You can specify individual families for the regular, bold, italic and bold+italic fonts. You can even specify specific font families for specific ranges of unicode characters. This allows precise control over text rendering. It can come in handy for applications like powerline, without the need to use patched fonts. See the various font related configuration directives in the config file.

Performance

The main goals for kitty performance are user perceived latency while typing and "smoothness" while scrolling as well as CPU usage. kitty tries hard to find an optimum balance for these. To that end it keeps a cache of each rendered glyph in video RAM so that font rendering is not a bottleneck. Interaction with child programs takes place in a separate thread from rendering, to improve smoothness.

There are two parameters you can tune to adjust the performance. repaint_delay and input_delay. These control the artificial delays introduced into the render loop to reduce CPU usage. See the config file for details. See also the sync_to_monitor option to further decrease latency at the cost of some tearing while scrolling.

You can generate detailed per-function performance data using gperftools. Build kitty with make profile which will create an executable called kitty-profile. Run that and perform the task you want to analyse, for example, scrolling a large file with less. After you quit, function call statistics will be printed to stdout and you can use tools like kcachegrind for more detailed analysis.

Here are some CPU usage numbers for the task of scrolling a file continuously in less. The CPU usage is for the terminal process and X together and is measured using htop. The measurements are taken at the same font and window size for all terminals on a Intel® Core™ i7-4820K CPU @ 3.70GHz CPU with a Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde XT [Radeon HD 7770/8760 / R7 250X] GPU.

Terminal	CPU usage (X + terminal)
kitty	6 - 8%
xterm	5 - 7% (but scrolling was extremely janky)
termite	10 - 13%
urxvt	12 - 14%
gnome-terminal	15 - 17%
konsole	29 - 31%

As you can see, kitty uses much less CPU than all terminals, except xterm, but its scrolling "smoothness" is much better than that of xterm (at least to my, admittedly biased, eyes).

Note for Linux/macOS packagers

While kitty does use python, it is not a traditional python package, so please do not install it in site-packages. Instead run,

python3 setup.py linux-package

This will install kitty into the directory linux-package. You can run kitty with linux-package/bin/kitty. All the files needed to run kitty will be in linux-package/lib/kitty. The terminfo file will be installed into linux-package/share/terminfo. Simply copy these files into /usr to install kitty. In other words, linux-package is the staging area into which kitty is installed. You can choose a different staging area, by passing the --prefix argument to setup.py.

You should probably split kitty into two packages, kitty-terminfo that installs the terminfo file and kitty that installs the main program. This allows users to install the terminfo file on servers into which they ssh, without needing to install all of kitty.

This applies to creating packages for kitty for macOS package managers such as brew or MacPorts as well.

Frequently Asked Questions

Some special symbols are rendered small/truncated in kitty?

The number of cells a unicode character takes up are controlled by the unicode standard. All characters are rendered in a single cell unless the unicode standard says they should be rendered in two cells. When a symbol does not fit, it will either be rescaled to be smaller or truncated (depending on how much extra space it needs). This is often different from other terminals which just let the character overflow into neighboring cells, which is fine if the neighboring cell is empty, but looks terrible if it is not.

Some programs, like powerline, vim with fancy gutter symbols/status-bar, etc. misuse unicode characters from the private use area to represent symbols. Often these symbols are square and should be rendered in two cells. However, since private use area symbols all have their width set to one in the unicode standard, kitty renders them either smaller or truncated. The exception is if these characters are followed by a space or empty cell in which case kitty makes use of the extra cell to render them in two cells.

How do I build kitty.app on macOS?

Install optipng and librsvg using brew or similar (needed for the logo generation step).

And run:

make app

This kitty.app unlike the released one does not include its own copy of python and the other dependencies. So if you ever un-install/upgrade those dependencies you might have to rebuild the app.

Note that the released kitty.dmg includes all dependencies, unlike the kitty.app built above and is built automatically by using the kitty branch of build-calibre however, that is designed to run on Linux and is not for the faint of heart.

Using a color theme with a background color does not work well in vim?

First make sure you have not changed the TERM environment variable, it should be xterm-kitty. vim uses background color erase even if the terminfo file does not contain the bce capability. This is a bug in vim. You can work around it by adding the following to your vimrc:

let &t_ut=''

See here for why kitty does not support background color erase.

I get errors about the terminal being unknown or opening the terminal failing when SSHing into a different computer?

This happens because the kitty terminfo files are not available on the server. Either install kitty on the server, or simply copy over the terminfo files, using:

ssh myserver mkdir -p \~/.terminfo
infocmp xterm-kitty | ssh myserver "cat > /tmp/kitty.terminfo"
ssh myserver tic -x -o \~/.terminfo /tmp/kitty.terminfo

Really, the correct solution for this is to convince the OpenSSH maintainers to have ssh do this automatically when connecting to a server, so that all terminals work transparently.

Resources on terminal behavior

http://invisible-island.net/xterm/ctlseqs/ctlseqs.html

https://en.wikipedia.org/wiki/C0_and_C1_control_codes

https://vt100.net/