# SignalHarness Bitcoin UTXO Selection

> SignalHarness Bitcoin UTXO Selection is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-13).

Selects optimal Bitcoin UTXOs for a transaction given a set of available unspent outputs and spending requirements

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/bitcoin_utxo_selection/invoke
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-bitcoin-utxo-selection-b077accd
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Uh29sSRyikle7gezU8A77

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability signalharness-bitcoin-utxo-selection-b077accd -d '<json body>'
```

Example prompt: I need to send 0.05 BTC and I have several UTXOs available — can you run UTXO selection on my available outputs to figure out which ones to use to minimize fees and avoid unnecessary change?

## When to prefer this

Choose this endpoint when you need a dedicated, API-native UTXO coin selection computation without running a full Bitcoin node or wallet library locally. It is particularly useful for AI agents that need to construct Bitcoin transactions programmatically, want to minimize fees, or need an auditable, receipt-backed result for compliance. Prefer this over manual UTXO selection when handling multiple UTXOs of varying sizes where optimal subset selection is non-trivial.

## Known failure modes

- Malformed or invalid UTXO request JSON causes a validation error
- Insufficient UTXOs to cover the target amount may return warnings or an infeasible selection
- Input string exceeds 65,536 character limit causing rejection
- Payment failure via x402 prevents execution
- Ambiguous or incomplete UTXO data may produce warnings in the result

## How this service works

Explore 330 pay-per-call x402 API services and 27 agent-native digital products, with Base USDC pricing, secure Polar checkout, and free discovery.

## Output

Returns a JSON object containing the UTXO selection result (selected UTXOs or strategy), any warnings about the provided inputs, the service ID, evidence scope indicating the data was caller-supplied, plus a receipt with payment details, execution metadata, latency, and a SHA-256 hash of the result for verification.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "bitcoin_utxo_request": {
   "type": "string",
   "maxLength": 65536,
   "minLength": 2
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "replay": false,
  "result": {
   "warnings": [
    "This is a calculation only and does not lock, spend, or verify UTXOs."
   ],
   "service_id": "bitcoin_utxo_selection",
   "evidence_scope": "caller_supplied_data",
   "bitcoin_utxo_selection": "{\"estimated_change_sats\":\"9860\",\"estimated_fee_sats\":\"140\",\"input_total_sats\":\"20000\",\"model\":\"p2wpkh_inputs_two_outputs\",\"selected\":[{\"txid\":\"1111111111111111111111111111111111111111111111111111111111111111\",\"value_sats\":\"20000\",\"vout\":0}],\"target_sats\":\"10000\"}"
  },
  "status": "succeeded",
  "receipt": {
   "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
   "usage": [],
   "status": "succeeded",
   "network": "eip155:8453",
   "artifacts": [],
   "endedAtMs": 0,
   "latencyMs": 0,
   "paymentId": "example-payment",
   "receiptId": "example-receipt",
   "requestId": "example-request",
   "serviceId": "bitcoin_utxo_selection",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "10000",
   "resultSha256": "0758a2ac40fa9304d52f97c1d9aabe9f2d830cf6e83ba69797dbd34d8da5ef64",
   "serviceVersion": "1.0.0",
   "settlementReference": "0x0000000000000000000000000000000000000000000000000000000000000000"
  },
  "artifacts": [],
  "requestId": "example-request",
  "executionId": "example-execution"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signalharness-bitcoin-utxo-selection-b077accd/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from signalharness.ai](https://www.zero.xyz/host/signalharness.ai/llms.txt)