Transaction ID (TXID)

A transaction ID, or TXID, is the unique identifier given to each transaction on a blockchain, usually shown as a long string of hexadecimal characters. It is produced by running the transaction's data through a cryptographic hash function; in Bitcoin this means applying SHA-256 twice, so any change to the transaction would produce a completely different ID. Because of this, the term is often used interchangeably with transaction hash. Users paste a TXID into a block explorer to check whether a payment has been included in a block, see its amount and fees, and count its confirmations. Exchanges and support teams ask for TXIDs to trace missing deposits. Before the SegWit upgrade, Bitcoin TXIDs could be altered by third parties without changing a transaction's effect, a flaw known as transaction malleability, which SegWit fixed. Payment systems such as SWIFT use comparable references.