# SignalHarness Agent Tool Call Validator

> SignalHarness Agent Tool Call Validator is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-15).

Validates an AI agent tool call JSON payload for correctness, schema compliance, and potential issues before execution

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/agent_tool_call_validate/invoke
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-agent-tool-call-validator-2691f07d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_wsQ9nHoqmXDxnMQkA1OAx

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-agent-tool-call-validator-2691f07d -d '<json body>'
```

Example prompt: Before I execute this tool call, can you validate the following JSON payload to make sure it's correctly formed and flag any warnings: {"tool": "send_email", "params": {"to": "alice@example.com", "subject": "Hello"}}?

## When to prefer this

Choose this endpoint when you need a lightweight, pay-per-call validation layer for AI agent tool call JSON before execution — especially useful in automated pipelines where catching malformed payloads early prevents downstream failures. Prefer it over manual schema checks when you want a structured analysis with warnings and an auditable receipt, or when operating within a Base USDC x402 payment environment.

## Known failure modes

- Malformed or non-JSON request_json string returns a validation error
- Payload exceeding 65,536 characters is rejected
- Missing required request_json field causes a bad request response
- Ambiguous or empty JSON (below 2 characters) is rejected by minLength constraint
- Payment failure on the x402 protocol may prevent invocation

## 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 validation result object containing a status (succeeded/failed), a boolean replay flag, an analysis_json string with structured findings, a list of warnings about the payload, an evidence_scope label (e.g. caller_supplied_data), and a full receipt with payment metadata, latency, and a SHA-256 hash of the result.

## 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": "agent_tool_call_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": "agent_tool_call_validate",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "5000",
   "resultSha256": "c824d3b775a0c55472193d1aa39beb5925c92b05148ebe3af552a8f049a96277",
   "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-agent-tool-call-validator-2691f07d/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)