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# Custom kittens

You can easily create your own kittens to extend kitty. They are just terminal programs written in Python. When launching a kitten, kitty will open an overlay window over the current window and optionally pass the contents of the current window/scrollback to the kitten over its `STDIN`. The kitten can then perform whatever actions it likes, just as a normal terminal program. After execution of the kitten is complete, it has access to the running kitty instance so it can perform arbitrary actions such as closing windows, pasting text, etc.

Let’s see a simple example of creating a kitten. It will ask the user for some input and paste it into the terminal window.

Create a file in the kitty config directory, `~/.config/kitty/mykitten.py` (you might need to adjust the path to wherever the kitty config directory is on your machine).

    from kitty.boss import Boss

    def main(args: list[str]) -> str:
        # this is the main entry point of the kitten, it will be executed in
        # the overlay window when the kitten is launched
        answer = input('Enter some text: ')
        # whatever this function returns will be available in the
        # handle_result() function
        return answer

    def handle_result(args: list[str], answer: str, target_window_id: int, boss: Boss) -> None:
        # get the kitty window into which to paste answer
        w = boss.window_id_map.get(target_window_id)
        if w is not None:
            w.paste_text(answer)

Now in `kitty.conf` add the lines:

    map ctrl+k kitten mykitten.py

Start kitty and press `Ctrl`+`K` and you should see the kitten running. The best way to develop your own kittens is to modify one of the built-in kittens. Look in the kittens sub-directory of the kitty source code for those. Or see below for a list of third-party kittens, that other kitty users have created.

## kitty API to use with kittens

Kittens have full access to internal kitty APIs. However these are neither entirely stable nor documented. You can instead use the kitty Remote control API. Simply call `boss.call_remote_control()`, with the same arguments you would pass to `kitten @`. For example:

    def handle_result(args: list[str], answer: str, target_window_id: int, boss: Boss) -> None:
        # get the kitty window to which to send text
        w = boss.window_id_map.get(target_window_id)
        if w is not None:
            boss.call_remote_control(w, ('send-text', f'--match=id:{w.id}', 'hello world'))

Note

Inside handle_result() the active window is still the window in which the kitten was run, therefore when using call_remote_control() be sure to pass the appropriate option to select the target window, usually `--match` as shown above or `--self`.

Run, `kitten @ --help` in a kitty terminal, to see all the remote control commands available to you.

## Passing arguments to kittens

You can pass arguments to kittens by defining them in the map directive in `kitty.conf`. For example:

    map ctrl+k kitten mykitten.py arg1 arg2

These will be available as the `args` parameter in the `main()` and `handle_result()` functions. Note also that the current working directory of the kitten is set to the working directory of whatever program is running in the active kitty window. The special argument `@selection` is replaced by the currently selected text in the active kitty window.

## Passing the contents of the screen to the kitten

If you would like your kitten to have access to the contents of the screen and/or the scrollback buffer, you just need to add an annotation to the `handle_result()` function, telling kitty what kind of input your kitten would like. For example:

    from kitty.boss import Boss

    # in main, STDIN is for the kitten process and will contain
    # the contents of the screen
    def main(args: list[str]) -> str:
        return sys.stdin.read()

    # in handle_result, STDIN is for the kitty process itself, rather
    # than the kitten process and should not be read from.
    from kittens.tui.handler import result_handler
    @result_handler(type_of_input='text')
    def handle_result(args: list[str], stdin_data: str, target_window_id: int, boss: Boss) -> None:
        pass

This will send the plain text of the active window to the kitten’s `STDIN`. There are many other types of input you can ask for, described in the table below:

Types of input to kittens
Keyword | Type of `STDIN` input
--- | ---
`text` | Plain text of active window
`ansi` | Formatted text of active window
`screen` | Plain text of active window with line wrap markers
`screen-ansi` | Formatted text of active window with line wrap markers
`history` | Plain text of active window and its scrollback
`ansi-history` | Formatted text of active window and its scrollback
`screen-history` | Plain text of active window and its scrollback with line wrap markers
`screen-ansi-history` | Formatted text of active window and its scrollback with line wrap markers
`output` | Plain text of the output from the last run command
`output-screen` | Plain text of the output from the last run command with wrap markers
`output-ansi` | Formatted text of the output from the last run command
`output-screen-ansi` | Formatted text of the output from the last run command with wrap markers
`selection` | The text currently selected with the mouse

In addition to `output`, that gets the output of the last run command, `last_visited_output` gives the output of the command last jumped to and `first_output` gives the output of the first command currently on screen. These can also be combined with `screen` and `ansi` for formatting.

Note

For the types based on the output of a command, Shell integration is required.

## Using kittens to script kitty, without any terminal UI

If you would like your kitten to script kitty, without bothering to write a terminal program, you can tell the kittens system to run the `handle_result()` function without first running the `main()` function.

For example, here is a kitten that “zooms in/zooms out” the current terminal window by switching to the stack layout or back to the previous layout. This is equivalent to the builtin `toggle_layout` action.

Create a Python file in the kitty config directory, `~/.config/kitty/zoom_toggle.py`

    from kitty.boss import Boss

    def main(args: list[str]) -> str:
        pass

    from kittens.tui.handler import result_handler
    @result_handler(no_ui=True)
    def handle_result(args: list[str], answer: str, target_window_id: int, boss: Boss) -> None:
        tab = boss.active_tab
        if tab is not None:
            if tab.current_layout.name == 'stack':
                tab.last_used_layout()
            else:
                tab.goto_layout('stack')

Now in `kitty.conf` add:

    map f11 kitten zoom_toggle.py

Pressing `F11` will now act as a zoom toggle function. You can get even more fancy, switching the kitty OS window to fullscreen as well as changing the layout, by simply adding the line:

    boss.toggle_fullscreen()

to the `handle_result()` function, above.

## Sending mouse events

If the program running in a window is receiving mouse events, you can simulate those using:

    from kitty.fast_data_types import send_mouse_event
    send_mouse_event(screen, x, y, button, action, mods)

`screen` is the `screen` attribute of the window you want to send the event to. `x` and `y` are the 0-indexed coordinates. `button` is a number using the same numbering as X11 (left: `1`, middle: `2`, right: `3`, scroll up: `4`, scroll down: `5`, scroll left: `6`, scroll right: `7`, back: `8`, forward: `9`). `action` is one of `PRESS`, `RELEASE`, `DRAG` or `MOVE`. `mods` is a bitmask of `GLFW_MOD_{mod}` where `{mod}` is one of `SHIFT`, `CONTROL` or `ALT`. All the mentioned constants are imported from `kitty.fast_data_types`.

For example, to send a left click at position x: 2, y: 3 to the active window:

    from kitty.fast_data_types import send_mouse_event, PRESS
    send_mouse_event(boss.active_window.screen, 2, 3, 1, PRESS, 0)

The function will only send the event if the program is receiving events of that type, and will return `True` if it sent the event, and `False` if not.

## Using remote control inside the main() kitten function

You can use kitty’s remote control features inside the main() function of a kitten, even without enabling remote control. This is useful if you want to probe kitty for more information before presenting some UI to the user or if you want the user to be able to control kitty from within your kitten’s UI rather than after it has finished running. To enable it, simply tell kitty your kitten requires remote control, as shown in the example below:

    import json
    import sys
    from pprint import pprint

    from kittens.tui.handler import kitten_ui

    @kitten_ui(allow_remote_control=True)
    def main(args: list[str]) -> str:
        # get the result of running kitten @ ls
        cp = main.remote_control(['ls'], capture_output=True)
        if cp.returncode != 0:
            sys.stderr.buffer.write(cp.stderr)
            raise SystemExit(cp.returncode)
        output = json.loads(cp.stdout)
        pprint(output)
        # open a new tab with a title specified by the user
        title = input('Enter the name of tab: ')
        window_id = main.remote_control(['launch', '--type=tab', '--tab-title', title], check=True, capture_output=True).stdout.decode()
        return window_id

`allow_remote_control=True` tells kitty to run this kitten with remote control enabled, regardless of whether it is enabled globally or not. To run a remote control command use the `main.remote_control()` function which is a thin wrapper around Python’s `subprocess.run` function. Note that by default, for security, child processes launched by your kitten cannot use remote control, thus it is necessary to use `main.remote_control()`. If you wish to enable child processes to use remote control, call `main.allow_indiscriminate_remote_control()`.

Remote control access can be further secured by using `kitten_ui(allow_remote_control=True, remote_control_password='ls set-colors')`. This will use a secure generated password to restrict remote control. You can specify a space separated list of remote control commands to allow, see `remote_control_password` for details. The password value is accessible as `main.password` and is used by `main.remote_control()` automatically.

## Debugging kittens

The part of the kitten that runs in `main()` is just a normal program and the output of print statements will be visible in the kitten window. Or alternately, you can use:

    from kittens.tui.loop import debug
    debug('whatever')

The `debug()` function is just like `print()` except that the output will appear in the `STDOUT` of the kitty process inside which the kitten is running.

The `handle_result()` part of the kitten runs inside the kitty process. The output of print statements will go to the `STDOUT` of the kitty process. So if you run kitty from another kitty instance, the output will be visible in the first kitty instance.

## Developing builtin kittens for inclusion with kitty

There is documentation for Developing builtin kittens which are written in the Go language.

## Kittens created by kitty users

vim-kitty-navigator

  Allows you to navigate seamlessly between vim and kitty splits using a consistent set of hotkeys.

smart-scroll

  Makes the kitty scroll bindings work in full screen applications

kitty-tab-switcher

  Fuzzy finder for kitty tabs with previews

gattino

  Integrate kitty with an LLM to convert plain language prompts into shell commands.

insert password

  Insert a password from a CLI password manager, taking care to only do it at a password prompt.

weechat-hints

  URL hints kitten for WeeChat that works without having to use WeeChat’s raw-mode.