Transaction ID

A transaction ID, often shortened to TXID or called a transaction hash, is the unique fingerprint a blockchain network assigns to every transfer of value. It is produced by running the transaction's full data, its inputs, outputs, amounts and signatures, through a cryptographic hashing algorithm, so the result is deterministic: the same transaction always produces the same ID, and altering even one byte of the underlying data changes it completely.

On Bitcoin, the TXID is created by double-hashing the serialized transaction with SHA-256, producing a 64-character hexadecimal string. Ethereum and other EVM-compatible chains instead hash the transaction fields with Keccak-256 and prefix the result with "0x". Whatever the exact method, the ID lets anyone paste it into a block explorer to look up the sender and recipient addresses, the amount moved, the network fee paid and the number of confirmations it has received.

Because it works like a receipt number, a TXID is the standard proof of payment between exchanges, wallets and merchants, and support teams routinely ask users for it to trace a deposit or withdrawal. Early Bitcoin transactions were vulnerable to "malleability", where a third party could tweak a signature in transit and change a transaction's ID without altering what it actually did, an issue widely cited among the factors behind the Mt. Gox exchange's 2014 collapse. The 2017 SegWit upgrade largely closed this loophole by excluding signature data from the ID calculation, making TXIDs a stable, trustworthy reference the moment a transaction is broadcast to the network.