# init(blockChecked:powValidBlock:blockConnected:blockDisconnected:) Creates validation interface callbacks. ``` init(blockChecked: ((Block, BlockValidationState) -> Void)? = nil, powValidBlock: ((Block, BlockTreeEntrySnapshot) -> Void)? = nil, blockConnected: ((Block, BlockTreeEntrySnapshot) -> Void)? = nil, blockDisconnected: ((Block, BlockTreeEntrySnapshot) -> Void)? = nil) ``` ## Parameters `blockChecked` Handler for blocks that have been fully validated. See [`blockChecked`](/documentation/BitcoinKernel/ValidationInterfaceCallbacks/blockChecked). `powValidBlock` Handler for blocks with valid proof-of-work added to the header chain. See [`powValidBlock`](/documentation/BitcoinKernel/ValidationInterfaceCallbacks/powValidBlock). `blockConnected` Handler for blocks connected to the best chain. See [`blockConnected`](/documentation/BitcoinKernel/ValidationInterfaceCallbacks/blockConnected). `blockDisconnected` Handler for blocks removed from the best chain during a re-org. See [`blockDisconnected`](/documentation/BitcoinKernel/ValidationInterfaceCallbacks/blockDisconnected). ## Discussion Set only the callbacks you need; unset callbacks are ignored. All closures are captured at init time and cannot be changed later.