Block Header

A block header is a compact summary of a block in a blockchain. While each block contains a list of transactions, the block header holds essential metadata that identifies and secures the block. Key elements in a block header include:

• Block height: How many blocks exist before this one in the chain.
• Block hash: A unique cryptographic fingerprint of the block header, used as proof that computational work was done.
• Previous block hash: Connects this block to the one before it, keeping the sequence tamper-resistant.
• Timestamp: When the block was created or published.
• Merkle root: A single hash representing all the transactions inside the block.
• Difficulty (bits): Indicates how challenging it was to find a valid block hash.
• Nonce: A variable number miners change to try to find a valid block hash.

Block headers are much smaller than full blocks, so they can be shared and processed quickly across the network. When miners compete to add new blocks, they repeatedly hash the block header—not the entire block—while searching for a hash that meets the proof-of-work requirement. This approach keeps the mining process efficient; otherwise, miners would be incentivized to mine blocks without transactions for faster hashing, which would harm the network’s capacity to process payments.