UTXO Model

Overview

A transaction selects one or more existing UTXOs as inputs. The owner satisfies their locking conditions through signatures or scripts. The transaction then creates new outputs for recipients and usually a change output for the sender. Input value must cover output value plus fees.

The model provides clear transaction dependencies and parallel validation. Transactions consuming different outputs do not compete for one shared account nonce. Each UTXO can be checked independently against the current UTXO set.

Double spending is prevented because a canonical transaction can consume an output only once. Conflicting transactions that reference the same output cannot both remain valid in the accepted chain.

The model affects privacy and fees. Combining multiple inputs can link addresses, while many small outputs increase transaction size. Wallet software must perform coin selection and change management rather than simply subtracting from one account balance.

Smart-contract design differs from account-based systems. Extended UTXO models attach data and scripts to outputs, enabling application state machines while retaining explicit input consumption.

The UTXO model is not inherently more or less scalable or private than an account model. Its strengths and trade-offs depend on scripting, block capacity, wallet behavior, and application architecture. It is fundamentally a method of representing spendable state through discrete outputs.

The explicit-output structure can support more local reasoning about ownership because each input names exactly what it consumes. However, complex applications may need off-chain coordination to locate suitable outputs and avoid contention. Extended UTXO systems add richer data but retain the rule that shared state must be represented through spendable objects, changing how developers design concurrency and user interactions.