Minecraft wiki entry for Command_Block, associated text: To enter command or modify the command block, use the Use Item control on the command block to open the command block GUI (graphical user interface). The GUI opens only if the player is in Creative mode, and has the proper permissions. That means, in singleplayer, "Allow Cheats"‌[JE only] or "Activate Cheats"‌[BE only] in options must be enabled. In multiplayer, Gui can be opened only by operators in Creative mode, and in Java Edition op-permission-level in the server.properties file must be set to 2 or above (default is 4).