Bitcoin UTXO Identity: Transaction ID and Output Index
Use Bitcoin outpoints to identify spendable outputs, resolve input references correctly, and avoid treating a transaction ID as a unique holding.
Overview
When translating these concepts into an integration, keep the scope described by the wallet history api with the result. The examples in wallet transaction history and smart contract event logs show how the same distinction affects neighbouring data questions.
A Bitcoin output is identified by an outpoint: transaction ID plus output index. One transaction can create many outputs, and later inputs spend particular outputs rather than an undifferentiated transaction balance.
Keep the pair together
Store txid and vout as separate typed fields or a documented composite key. Resolve each input’s referenced output to obtain the value and script it spends. A transaction hash without an output index cannot tell which of several outputs is being referenced. Preserve network identity as part of application storage and cache boundaries.
Worked example: two outputs to one wallet
Transaction T creates outputs zero and two that both belong to a wallet. Spending T:0 does not spend T:2. A store keyed only by T can mistakenly remove both holdings. Outpoint-level state keeps the second output available and makes the spending relationship auditable.
Track accepted spend state
Record the creating and spending transactions and their accepted block context. Test duplicate input processing, reorganisations and an output whose historical detail is unavailable. A current UTXO lookup answers whether an output is unspent under that view; it is not a complete historical record of every output the wallet ever controlled.
A practical acceptance test
Create two wallet-owned outputs under one transaction ID and spend only the first. The second must remain unspent. Repeat the spending input delivery and verify no additional decrease. Then displace the spending block under the fixture’s accepted-chain model and restore the appropriate output state while preserving the original observation history.
Questions about the topic
Frequently asked questions
Is a transaction ID a UTXO ID?
Not by itself; the output index is required.
Does spending one output spend all outputs of that transaction?
No. Inputs reference specific outpoints.
Standards & technical documentation
