# SignalHarness LLM Response Schema Validator

> SignalHarness LLM Response Schema Validator is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-16).

Validates a JSON string produced by an LLM against an expected schema, returning warnings and analysis about schema compliance.

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/llm_response_schema_validate/invoke
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-llm-response-schema-validator-27d497ea
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Fa9yd-kSYMnVfqQOkhCAn

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-llm-response-schema-validator-27d497ea -d '<json body>'
```

Example prompt: Can you validate this JSON string my LLM just produced and tell me if it's schema-compliant: '{"name":"Alice","age":30}'?

## When to prefer this

Use this endpoint when you need a fast, pay-per-call schema validation of LLM-generated JSON output inside an agent pipeline, especially when you want a receipt-backed audit trail via x402/Base USDC micropayments. Prefer this over manual JSON parsing when you need structured compliance feedback with warnings, or when operating in an autonomous agent context that already uses SignalHarness x402 services.

## Known failure modes

- Invalid or non-parseable JSON string submitted as request_json — may return error or empty analysis
- request_json exceeds 65536 character limit — request rejected
- Malformed input that is not a JSON string — validation cannot proceed
- Network or payment failure — receipt status may reflect failed settlement

## 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 a status field ('succeeded'), a result object with an analysis_json string (schema compliance findings), a list of warnings about caller-supplied data, and a signed receipt with payment details, request/execution IDs, result hash, and latency metrics.

## 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": "llm_response_schema_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": "llm_response_schema_validate",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "5000",
   "resultSha256": "96eda6321d55be5af1bceb5cc506ca685922635a7cdbe2635bd1f5b7eabd45c7",
   "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-llm-response-schema-validator-27d497ea/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)