Transaction hashes form the leaves; adjacent hashes are concatenated and double-SHA-256 hashed repeatedly until one root remains. Bitcoin duplicates the final hash at an odd-width level. A Merkle proof provides the sibling path needed to verify inclusion against the header root without transferring every transaction, but inclusion alone does not prove the transaction or block is consensus-valid.
A deterministic binary hash tree that commits a block header’s Merkle root to every transaction identifier in the block. [Bitcoin Developer Guide — Merkle Trees] [Bitcoin whitepaper — Simplified Payment Verification] [Bitcoin Core — Merkle tree implementation]
Transaction hashes form the leaves; adjacent hashes are concatenated and double-SHA-256 hashed repeatedly until one root remains. Bitcoin duplicates the final hash at an odd-width level. A Merkle proof provides the sibling path needed to verify inclusion against the header root without transferring every transaction, but inclusion alone does not prove the transaction or block is consensus-valid. [Bitcoin Developer Guide — Merkle Trees] [Bitcoin whitepaper — Simplified Payment Verification] [Bitcoin Core — Merkle tree implementation]
A fully validating node reconstructs this result from raw blocks and transactions, applies the exact consensus rules locally and rejects invalid data even when a miner, explorer or majority of peers presents it. The verification path is reproducible and does not require trusting a website’s interpretation. [Bitcoin Developer Guide — Merkle Trees] [Bitcoin whitepaper — Simplified Payment Verification] [Bitcoin Core — Merkle tree implementation]
Proof of work orders only histories whose blocks are valid; it does not make invalid transactions valid or create instant mathematical finality. Reorganizations remain possible, resource requirements affect who verifies, and protocol structure alone does not guarantee privacy, custody safety or correct operational choices. [Bitcoin Developer Guide — Merkle Trees] [Bitcoin whitepaper — Simplified Payment Verification] [Bitcoin Core — Merkle tree implementation]
Use a current validating implementation, verify downloaded data and distinguish consensus validity from relay or mining policy. For important decisions inspect the underlying transaction, header, target and accumulated chainwork, keep software and backups controlled, and test procedures before relying on them with material value. [Bitcoin Developer Guide — Merkle Trees] [Bitcoin whitepaper — Simplified Payment Verification] [Bitcoin Core — Merkle tree implementation]
For the clearest picture, read this entry together with Block, Transaction, Block header. The reverse links also lead from Block header, Cryptographic hash, SHA-256, Confirmation.