# blockTreeEntry(byHash:) Looks up a block tree entry by its block hash. ``` func blockTreeEntry(byHash hash: BlockHash) -> BlockTreeEntry? ``` ## Parameters `hash` The block hash to look up. ## Return Value The matching [`BlockTreeEntry`](/documentation/BitcoinKernel/BlockTreeEntry), or `nil` if the kernel has no record of a block with that hash. ## Discussion Searches the full block index — which includes blocks on side chains the kernel has evaluated but not adopted, not just the active chain. Cheap: backed by an in-memory hash table.