# SignalHarness Prompt Variable Validator

> SignalHarness Prompt Variable Validator is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-13).

Validates the variables and structure within a prompt template JSON payload, returning warnings and analysis about the supplied data

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/prompt_variable_validate/invoke
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-prompt-variable-validator-48cae78a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_nYEQ7EUmViz_VhP-0xV9x

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-variable-validator-48cae78a -d '<json body>'
```

Example prompt: Can you validate this prompt template JSON to make sure the variables are correct before I use it in my agent pipeline? Here's the JSON: {"template": "Hello {{name}}, your order {{order_id}} is ready.", "variables": {"name": "string", "order_id": "string"}}

## When to prefer this

Choose this endpoint when you need a lightweight, pay-per-call validation step for prompt template variable JSON before using it in an agent pipeline. It's particularly useful in automated agent workflows where prompt templates are generated dynamically and need to be sanity-checked for structural correctness before incurring the cost of an LLM call. Prefer this over manual inspection or schema-only validators when you want structured warnings and analysis in a machine-readable format at minimal cost ($0.005 USDC per call).

## Known failure modes

- Malformed or non-JSON request_json input returns a validation error
- Payload exceeding 65536 characters is rejected
- Missing required request_json field causes a schema error
- Network or payment settlement failure may result in no receipt
- Ambiguous variable types may generate warnings rather than hard errors

## 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 with a status field ('succeeded'), a result containing analysis_json with the validation findings, any warnings about the caller-supplied data, the service_id, and an evidence_scope indicating the data was caller-supplied. Also includes a receipt with payment details, request/execution IDs, network info, and a result SHA256 hash.

## 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_variable_validate",
   "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_variable_validate",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "5000",
   "resultSha256": "3e533a77fdc2c5ba8fb607e27963497fbbe5bccc045778e1f483b77bc33665c2",
   "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-variable-validator-48cae78a/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)