# SignalHarness Agent Trace Loop Detector

> SignalHarness Agent Trace Loop Detector 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).

Analyzes agent execution trace data to detect loops, cycles, or repetitive patterns in agent reasoning or action sequences.

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/agent_trace_loop_detect/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-agent-trace-loop-detector-068af57d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_PWO4IwhBaOFWw1DgZwDwW

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-trace-loop-detector-068af57d -d '<json body>'
```

Example prompt: Can you check this agent execution trace for any loop or cycle patterns? Here's the trace JSON from my last run — I think the agent might be repeatedly calling the same tool without making progress.

## When to prefer this

Use this endpoint when you need a lightweight, pay-per-call loop detection check on an agent trace without setting up your own monitoring infrastructure. It is well-suited for post-hoc debugging, pre-deployment validation, or real-time safety checks in agent pipelines. Prefer this over manual trace inspection when dealing with complex or long execution histories.

## Known failure modes

- Invalid or malformed request_json payload returns an error
- request_json exceeding 65536 characters is rejected
- Ambiguous or incomplete trace data may yield inconclusive results with warnings
- Payment failure via x402 protocol prevents execution
- Non-JSON string content may cause parsing failures

## 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 result indicating whether a loop was detected (replay boolean), an analysis_json with details about identified patterns, a list of warnings (e.g. to verify caller-supplied data), and an evidence_scope field indicating the data source used. Also includes a full receipt with payment details, latency, and a SHA256 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_trace_loop_detect",
   "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_trace_loop_detect",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "10000",
   "resultSha256": "cbe5b25670888073117efc18dddaf6120f9c42b66a2f4e95f801149d9051829b",
   "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-trace-loop-detector-068af57d/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)