Transaction Output (TxOut)

A Transaction Output (TxOut) is a data structure within a blockchain transaction that defines the recipient and quantity of a cryptocurrency transfer. It contains two primary fields: a value (the amount of the native asset, e.g., satoshis in Bitcoin) and a locking script (often called scriptPubKey), which is a set of conditions that must be met to spend the value in the future. Conceptually, a TxOut creates an unspent output, which can later serve as an input to a new transaction. The complete set of all unspent transaction outputs across the network is known as the UTXO set, which represents the total spendable state of the blockchain.

The locking script within a TxOut is crucial for security and programmability. In Bitcoin, this script is typically a Pay-to-Public-Key-Hash (P2PKH) or Pay-to-Script-Hash (P2SH) construct that encumbers the funds with a cryptographic puzzle. To spend the output, a future transaction must provide a corresponding unlocking script (or scriptSig) that satisfies the conditions—most commonly by proving ownership of the private key associated with the public key hash. This model, where transactions chain together by consuming previous outputs, is the basis of the UTXO model, used by Bitcoin, Litecoin, and many others.

Transaction outputs are inherently discrete and immutable. Once created in a confirmed block, a TxOut cannot be altered. It exists as a single, indivisible unit; if a user wishes to spend only a portion of its value, the entire output must be consumed, and new outputs must be created for both the payment and any change returned to the sender. This is a key difference from the account-based model (used by Ethereum), where balances are stored as mutable state variables. The UTXO model offers advantages in parallel transaction verification and enhanced privacy through coin selection algorithms.

From a developer's perspective, analyzing TxOut data is essential for wallet balance calculation, constructing new transactions, and auditing the blockchain. A wallet scans the UTXO set to find outputs locked to addresses it controls, sums their values to determine the spendable balance, and selects specific outputs as inputs for a new payment. This process, known as coin selection, can optimize for fees, privacy, or efficiency. Understanding TxOuts is therefore fundamental to building applications that interact with UTXO-based blockchains.

A Transaction Output (TxOut) is a data structure within a blockchain transaction that specifies the recipient and the amount of cryptocurrency being sent. It consists of two primary components: a value field denoting the amount in satoshis (for Bitcoin) or wei (for Ethereum), and a locking script (often called scriptPubKey). This locking script defines the conditions that must be met to spend the funds in the future, typically requiring a cryptographic signature from the holder of the corresponding private key. In essence, a TxOut creates a new, unspent chunk of value on the blockchain, waiting to be claimed.

The locking script within a TxOut is crucial for security and functionality. In Bitcoin, this is most commonly a Pay-to-Public-Key-Hash (P2PKH) script, which locks funds to a specific Bitcoin address. More advanced scripts enable complex conditions, such as multi-signature requirements (multisig), timelocks, or custom logic as seen in smart contracts. A TxOut is considered an Unspent Transaction Output (UTXO) until it is referenced as an input in a subsequent transaction. The UTXO model, used by Bitcoin and others, treats these outputs as discrete, immutable objects that are either fully spent or completely unspent.

To spend a TxOut, a later transaction must reference it as a Transaction Input (TxIn). This input provides an unlocking script (or scriptSig) that satisfies the conditions set by the original TxOut's locking script. For a standard P2PKH output, this means providing a digital signature and the corresponding public key. The network's nodes validate this by executing the combined scripts. If the result is TRUE, the output is considered spent, and new TxOuts are created for the payment and any change. This chain of linked inputs and outputs forms the entire history of fund movement on a UTXO-based blockchain.

A Transaction Output (TxOut) is a data structure within a blockchain transaction that specifies the recipient and conditions for spending a specific amount of cryptocurrency. It is a core component of the Unspent Transaction Output (UTXO) model, acting as a discrete, indivisible packet of value. Each TxOut contains two primary fields: a value (the amount of the native asset, e.g., satoshis) and a locking script (often called scriptPubKey), which defines the cryptographic conditions that must be met to spend this output in a future transaction.

The locking script is the critical security and programmability element of a TxOut. In Bitcoin, this is a script written in a stack-based language that typically requires a digital signature corresponding to a public key hash (P2PKH) or a script hash (P2SH, P2WSH). In Ethereum and other account-based chains, the analogous concept is the recipient's account address. This script acts as a cryptographically-secured lockbox; only a subsequent transaction that provides a valid unlocking script (scriptSig or witness data) satisfying these conditions can reference this TxOut as an input, thereby "unlocking" and spending its value.

When a transaction is confirmed, its outputs become new UTXOs, added to the global set of spendable funds. A key rule is that a UTXO must be spent in its entirety. If the value of a TxOut is greater than needed, the transaction must create a second output, often sending the "change" back to the spender's own wallet. This model provides strong transactional privacy and parallelism but differs fundamentally from the account/balance model used by platforms like Ethereum, where state is maintained in continuously updated account balances.