Minecraft wiki entry for BE, associated text: Block entity data
Tags common to all block entities[show]
 auto: 1 or 0 (true/false) - Allows to activate the command without the requirement of a redstone signal.
 Command: The command to issue to the server.
 conditionMet: 1 or 0 (true/false) - Indicates whether a conditional command block had its condition met when last activated. True if not a conditional command block.
 CustomName: Optional. The name JSON text component of this command block, replacing the usual '@' when using commands such as /say and /tell.
 LastExecution: stores the tick a chain command block was last executed in.
 LastOutput: The last line of output generated by the command block. Still stored even if the gamerule commandBlockOutput is false. Appears in the GUI of the block when right-clicked, and includes a timestamp of when the output was produced.
 powered: 1 or 0 (true/false) - States whether or not the command block is powered by redstone or not.
 SuccessCount: Represents the strength of the analog signal output by redstone comparators attached to this command block.
 TrackOutput: 1 or 0 (true/false) - Determines whether the LastOutput is stored. Can be toggled in the GUI by clicking a button near the "Previous Output" textbox. Caption on the button indicates current state: "O" if true, "X" if false.
 UpdateLastExecution: 1 or 0 (true/false) - Defaults to true. If set to false, loops can be created where the same command block can run multiple times in one tick.