# SignalHarness Prompt Version Compare

> SignalHarness Prompt Version Compare is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.015/call, status unknown (last checked 2026-09-15).

Compares two or more versions of an LLM prompt to analyze differences, regressions, or improvements across prompt iterations

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/prompt_version_compare/invoke
- Price: $0.015/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-prompt-version-compare-d8868710
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_oQ0XNmYAOIxS-FwNIIBDi

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-prompt-version-compare-d8868710 -d '<json body>'
```

Example prompt: Compare these two prompt versions for me and tell me what changed and which looks stronger: version 1 is 'You are a helpful assistant. Answer questions concisely.' and version 2 is 'You are an expert assistant. Provide thorough, step-by-step answers with examples.'

## When to prefer this

Choose this endpoint when you need a structured, paid, auditable comparison of LLM prompt versions — especially in agent pipelines where you want a receipt-backed result with a result hash for verification. Prefer this over manual diffing or free tools when you need programmatic JSON output with auditability, or when operating in an x402 micropayment workflow on Base.

## Known failure modes

- Malformed or invalid request_json causes validation error
- Prompt version data missing or too short (minLength:2 not met)
- Payload exceeds 65536 character limit causing rejection
- Insufficient USDC balance for the $0.015 per-call fee
- Analysis may reflect only caller-supplied data with no external ground truth — results carry a verification warning

## 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 analysis object containing a comparison of the supplied prompt versions, any warnings about the caller-supplied data, the service ID, and a signed receipt with payment metadata including amount, network, and result hash for auditability.

## Request schema (JSON Schema)

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

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "replay": false,
  "result": {
   "warnings": [
    "Verify the caller-supplied data before relying on this result."
   ],
   "service_id": "prompt_version_compare",
   "analysis_json": "{\"example\":\"schema-valid caller-supplied data\"}",
   "evidence_scope": "caller_supplied_data"
  },
  "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": "prompt_version_compare",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "15000",
   "resultSha256": "a26d9692763c1b62d563885c3ade30c7377e84fcb8f58b032a2f3cee2fd35e82",
   "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-prompt-version-compare-d8868710/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)