wezterm/docs/config/lua/window-events/format-window-title.md

format-window-title

{{since('20210502-154244-3f7122cb')}}

The format-window-title event is emitted when the text for the window title needs to be recomputed.

This event is a bit special in that it is synchronous and must return as quickly as possible in order to avoid blocking the GUI thread.

The most notable consequence of this is that some functions that are asynchronous (such as wezterm.run_child_process) are not possible to call from inside the event handler and will generate a format-window-title: runtime error: attempt to yield from outside a coroutine error.

This example overrides the default window title with code that is equivalent to the default processing--not very useful except as a starting point for making your own title text:

wezterm.on('format-window-title', function(tab, pane, tabs, panes, config)
  local zoomed = ''
  if tab.active_pane.is_zoomed then
    zoomed = '[Z] '
  end

  local index = ''
  if #tabs > 1 then
    index = string.format('[%d/%d] ', tab.tab_index + 1, #tabs)
  end

  return zoomed .. index .. tab.active_pane.title
end)

The parameters to the event are:

• tab - the TabInformation for the active tab
• pane - the PaneInformation for the active pane
• tabs - an array containing TabInformation for each of the tabs in the window
• panes - an array containing PaneInformation for each of the panes in the active tab
• config - the effective configuration for the window

The return value of the event should be a string, and if it is then it will be used as the title text in the window title bar.

If the event encounters an error, or returns something that is not a string, then the default window title text will be computed and used instead.

Only the first format-window-title event will be executed; it doesn't make sense to define multiple instances of the event with multiple wezterm.on("format-window-title", ...) calls.