# processBlock(_:) Processes a block for validation and potential inclusion in the active chain — the workhorse of every sync run. ``` func processBlock(_ block: Block) -> (success: Bool, isNew: Bool) ``` ## Parameters `block` The block to process. ## Return Value A tuple of `(success, isNew)`. `success` is `true` if the kernel accepted the block OR already had it; inspect the post-call [`bestEntry`](/documentation/BitcoinKernel/ChainstateManager/bestEntry) to see whether this block became the new tip. `isNew` is `true` if the kernel had not previously seen this block. ## Discussion Runs `CheckBlock` + `ContextualCheckBlock` + `ConnectBlock` from Bitcoin Core’s [`validation.cpp`](https://github.com/bitcoin/bitcoin/blob/master/src/validation.cpp). On success, the chainstate advances; on a chain-reorg scenario the kernel may internally switch to a new best chain without any extra caller action. This call can take seconds on mainnet-sized blocks and is interruptible via [`interrupt()`](/documentation/BitcoinKernel/Context/interrupt()).