Block Header
A summary of the data in the block.
A block header is like the metadata at the top of a block of transactions.
The fields in the block header provide a unique summary of the entire block.
Example
Here’s the block header for block 123,456:
010000009500c43a25c624520b5100adf82cb9f9da72fd2447a496bc600b0000000000006cd862370395dedf1da2841ccda0fc489e3039de5f1ccddef0e834991a65600ea6c8cb4db3936a1ae3143991
Fields
| Field | Description |
|---|---|
| Version | The version of the block. |
| Previous Block Hash | The Block Hash of the block that this block is being built on top of. This is what “chains” the blocks together. |
| Merkle Root | All of the transactions in this block, hashed together. Basically provides a single-line summary of all the transactions in this block. |
| Time | When a miner is trying to mine this block, the Unix time at which this block header is being hashed is noted within the block header itself. |
| Bits | A shortened version of the Target. |
| Nonce | The field that miners change in order to try and get a hash of the block header (a Block Hash) that is below the Target. |
Data Structure
| Field | Size | Data |
|---|---|---|
| Version | 4 bytes | Little-endian |
| Previous Block Hash | 32 bytes | Little-endian |
| Merkle Root | 32 bytes | Little-endian |
| Time | 4 bytes | Little-endian |
| Bits | 4 bytes | Little-endian |
| Nonce | 4 bytes | Little-endian |
Tools
- Hash Block Header - Insert individual block header fields, and get the serialized block header and the Block Hash.