There are a lot of island commands you can do while playing skyblock, you can do /is help to see all of these commands and what they do. Some of the most basic commands are:

Command Description
/is help Shows you all the island commands
/is go Teleports you to your island
/is create Creates a new island
/is coop Adds a player as a co-op to your island (people lose this when they log off)
/is uncoop Removes a player as a co-op on your island
/is invite <playername> Invites a player to join your island
/is accept <playername> Accept an island invitation
/is leave Leave someone's island (as island member)
/is disband Delete your island (as island leader)
/is promote <playername> Promotes an island member to the next rank (Member->Moderator->Admin)
/is demote <playername> Demotes an island member
/is settings Allows you to change the settings of your island
/is permissions Allows you to change the permissions for different island ranks
/is ban <playername> Bans a player from your island
/is unban <playername> Unbans a player from your island
/is expel <playername> Kicks a visitor from your island
/is kick Kick a player from your island
/is missions View the missions menu
/is top Shows you the top islands
/is close Locks the island to the public
/is open Opens the island to the public
/is visit <playername> Visits a players island
/is biome Changes your island biome
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