Block Header
Fundamentals● Common
An 80-byte structure containing block metadata: version (4 bytes), previous block hash (32 bytes), merkle root (32 bytes), timestamp (4 bytes), difficulty target (4 bytes), and nonce (4 bytes). The double-SHA256 hash of the header must be below the target for a valid proof-of-work.
Technical Notes
Version field now used for BIP-9 soft fork signaling. Timestamp must be > median of last 11 blocks and < 2 hours in future. Nonce space (4 bytes) often exhausted; miners vary extranonce in coinbase or use version rolling (overt ASICBoost). Header hash is displayed in reverse byte order.
Metadata
Visibility: Public
Created:1/3/2026by System