UTXOs
On Bitcoin metaprotocols the unspent output is the unit that matters. An
address is a convenience; an asset lives at an outpoint, txid:vout, and
spending that outpoint is what moves it.
Reading the outputs
Section titled “Reading the outputs”curl -s https://api.bitcoinuniverse.io/mempool/api/address/<address>/utxo[ { "txid": "7910fdb3…", "vout": 1, "value": 13001007836500, "status": { "confirmed": true, "block_height": 899592 } }, { "txid": "0c3a384d…", "vout": 0, "value": 546, "status": { "confirmed": true, "block_height": 902138 } }]value is in satoshis. A run of 546-satoshi outputs in a wallet is a strong
hint that something is being carried, because that is the usual postage for an
inscription-bearing output. It is a hint, not evidence.
What an empty array means, and does not
Section titled “What an empty array means, and does not”An empty array means the address was read and holds no unspent outputs. That is a fact about the address.
A read that fails answers with an explicit unavailable response instead. It never answers with an empty array. Treat the two as completely different results, because they license opposite conclusions.
What this response does not tell you
Section titled “What this response does not tell you”The UTXO response says nothing about whether an output carries an inscription, a rune balance, an ARC-20 colored value, or any other protocol asset. That question is answered by a protocol index, not by the base chain.
This is why Core keeps a complete output inventory as a mutation gate for several protocols: before a transaction is prepared, every output it would spend is checked against the full protocol inventory, and an output the index has not examined is treated as unknown rather than as empty.
Asset-bearing outputs explains what that protection actually prevents.
Ownership models
Section titled “Ownership models”The registry records an ownership model per protocol, and it determines what “holding” even means.
| Model | What holds the asset | Protocols |
|---|---|---|
utxo | A specific unspent output. Spend it and the asset moves. | Ordinals, Bitmap, Names, Realms, Subrealms, Atomicals NFTs, and others |
balance | An indexed balance attached to an address rather than an output. | SRC-20 |
hybrid | An indexed balance whose evidence is anchored to outputs. | Runes, BRC-20, TAP, ARC-20, Alkanes, and others |
A utxo asset can be destroyed by an ordinary spend. A hybrid asset can be
destroyed by a malformed marker even in a transaction Bitcoin considers
perfectly valid. Both cases are covered in
asset-bearing outputs.
Splitting and combining
Section titled “Splitting and combining”Splitting and combining outputs are recorded in the registry as Wallet surface actions, not Core actions. Core reads outputs and builds marketplace transactions around them. Reshaping a wallet’s outputs is the wallet’s job.