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

format-tab-title

Since: nightly builds only

The format-tab-title event is emitted when the text for a tab 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-tab-title: runtime error: attempt to yield from outside a coroutine error.

This example overrides the default tab title so that the background color is blue for the active tab. This is partially redundant because there is already configuration for this in tab_bar_style, but it demonstrates that it is possible to format more than just the text shown in the tab.

wezterm.on("format-tab-title", function(tab, tabs, panes, config)
  if tab.is_active then
    return {
      {Background={Color="blue"}},
      {Text=tab.active_pane.title},
    }
  end
  return tab.active_pane.title
end)

The parameters to the event are:

• tab - the TabInformation for the active tab
• 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 can be:

• a string, holding the text to use for the tab title
• a table holding FormatItems as used in the wezterm.format function. This allows formatting style and color information for individual elements within the tab.

If the event encounters an error, or returns something that is not one of the types mentioned above, then the default tab title text will be computed and used instead.

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