Desktop notifications

kitty implements an extensible escape code (OSC 99) to show desktop notifications. It is easy to use from shell scripts and fully extensible to show title and body. Clicking on the notification can optionally focus the window it came from, and/or send an escape code back to the application running in that window.

The design of the escape code is partially based on the discussion in the defunct terminal-wg

The escape code has the form:

<OSC> 99 ; metadata ; payload <terminator>

Here <OSC> is <ESC>] and <terminator> is <ESC><backslash>. The metadata is a section of colon separated key=value pairs. Every key must be a single character from the set a-zA-Z and every value must be a word consisting of characters from the set a-zA-Z0-9-_/\+.,(){}[]*&^%$#@!`~. The payload must be interpreted based on the metadata section. The two semi-colons must always be present even when no metadata is present.

Before going into details, lets see how one can display a simple, single line notification from a shell script:

printf '\x1b]99;;Hello world\x1b\\'

To show a message with a title and a body:

printf '\x1b]99;i=1:d=0;Hello world\x1b\\'
printf '\x1b]99;i=1:d=1:p=body;This is cool\x1b\\'

The most important key in the metadata is the p key, it controls how the payload is interpreted. A value of title means the payload is setting the title for the notification. A value of body means it is setting the body, and so on, see the table below for full details.

The design of the escape code is fundamentally chunked, this is because different terminal emulators have different limits on how large a single escape code can be. Chunking is accomplished by the i and d keys. The i key is the notification id which can be any string containing the characters [a-zA-Z0-9_-+.]. The d key stands for done and can only take the values 0 and 1. A value of 0 means the notification is not yet done and the terminal emulator should hold off displaying it. A value of 1 means the notification is done, and should be displayed. You can specify the title or body multiple times and the terminal emulator will concatenate them, thereby allowing arbitrarily long text (terminal emulators are free to impose a sensible limit to avoid Denial-of-Service attacks).

Both the title and body payloads must be either UTF-8 encoded plain text with no embedded escape codes, or UTF-8 text that is base64 encoded, in which case there must be an e=1 key in the metadata to indicate the payload is base64 encoded.

When the user clicks the notification, a couple of things can happen, the terminal emulator can focus the window from which the notification came, and/or it can send back an escape code to the application indicating the notification was activated. This is controlled by the a key which takes a comma separated set of values, report and focus. The value focus means focus the window from which the notification was issued and is the default. report means send an escape code back to the application. The format of the returned escape code is:

<OSC> 99 ; i=identifier ; <terminator>

The value of identifier comes from the i key in the escape code sent by the application. If the application sends no identifier, then the terminal must use i=0. Actions can be preceded by a negative sign to turn them off, so for example if you do not want any action, turn off the default focus action with:

a=-focus

Complete specification of all the metadata keys is in the table below. If a terminal emulator encounters a key in the metadata it does not understand, the key must be ignored, to allow for future extensibility of this escape code. Similarly if values for known keys are unknown, the terminal emulator should either ignore the entire escape code or perform a best guess effort to display it based on what it does understand.

Note

It is possible to extend this escape code to allow specifying an icon for the notification, however, given that some platforms, such as macOS, dont allow displaying custom icons on a notification, at all, it was decided to leave it out of the spec for the time being.

Similarly, features such as scheduled notifications could be added in future revisions.

Key

Value

Default

Description

a

Comma separated list of report, focus, with optional leading -

focus

What action to perform when the notification is clicked

d

0 or 1

1

Indicates if the notification is complete or not.

e

0 or 1

0

If set to 1 means the payload is base64 encoded UTF-8, otherwise it is plain UTF-8 text with no C0 control codes in it

i

[a-zA-Z0-9-_+.]

0

Identifier for the notification

p

One of title or body.

title

Whether the payload is the notification title or body. If a notification has no title, the body will be used as title.

Note

kitty also supports the legacy OSC 9 protocol developed by iTerm2 for desktop notifications.