# 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 folder, `~/.config/kitty/mykitten.py` (you might need to adjust the path to wherever the kitty config folder is on your machine).

    def main(args):
       # 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, answer, target_window_id, boss):
       # 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(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.

## 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.

## 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:

    # in main, STDIN is for the kitten process and will contain
    # the contents of the screen
    def main(args):
       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.
    def handle_result(args, stdin_data, target_window_id, boss):
       pass

    handle_result.type_of_input = 'text'

This will send the plain text of the active window to the kitten’s `STDIN`. For text with formatting escape codes, use `ansi` instead. If you want line wrap markers as well, use `screen-ansi` or just `screen`. For the scrollback buffer as well, use `history`, `ansi-history` or `screen-history`.

## 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/unzooms” the current terminal window by switching to the stack layout or back to the previous layout.

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

    def main(args):
       pass

    def handle_result(args, answer, target_window_id, boss):
       tab = boss.active_tab
       if tab is not None:
          if tab.current_layout.name == 'stack':
             tab.last_used_layout()
          else:
             tab.goto_layout('stack')

    handle_result.no_ui = True

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.

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