Candidate Block
Web3 / mining staking
A candidate block is a block that a miner or validator has constructed and is actively attempting to add to the blockchain. It contains a valid subset of pending transactions selected from the mempool, along with a reference to the previous block's hash, a timestamp, and other metadata required by the protocol. Miners compete to solve the cryptographic puzzle for a candidate block through proof-of-work, or validators propose candidate blocks in proof-of-stake systems. Not all candidate blocks will be added to the chain; only one per slot or round is typically accepted, while others are discarded and the transactions in them return to the mempool for future inclusion. Example: In Bitcoin mining, a miner builds a candidate block by selecting the highest-fee transactions from the mempool, adding a coinbase transaction that rewards themselves, and then repeatedly modifying a nonce value while computing SHA-256 hashes until finding one below the network's difficulty target. Why it matters for mining and staking: Understanding candidate blocks clarifies how miners and validators prioritize transactions and earn rewards. It also explains mempool dynamics and why some transactions may be delayed—if not included in any candidate block, they remain pending until a future block is proposed.
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