List of valid placeholders:
||The name of the player currently viewing the menu.|
||The amount of money owned by the player viewing the menu (requires a valid economy).|
||The world of the player viewing the menu.|
||Number of online players in the server.|
||Number of maximum player slots in the server.|
You can also use placeholders from PlaceholderAPI if the plugin is installed. PlaceholderAPI provides placeholders for a wide range of plugins.
Note: you must use the format with percent signs, for example