# Eval Engine API — Pay-per-call AI Evaluation

> Eval Engine API — Pay-per-call AI Evaluation is a paid API for AI agents from eval.zuluworksai.com, paid per call via x402, $0.005/call, status down (last checked 2026-09-15).

Scores LLM outputs and agent trajectories against benchmark rubrics using a pay-per-call evaluation engine.

## Facts

- Endpoint: POST https://eval.zuluworksai.com/eval
- Price: $0.005/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/eval-engine-api-pay-per-call-ai-evaluation-034014af
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_PAT9HemP1UdvA2ynk8RFD

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 eval-engine-api-pay-per-call-ai-evaluation-034014af -d '<json body>'
```

Example prompt: Score this agent trajectory against benchmark 'tool-use-v1' and tell me how well it did: 'User asked for weather → agent called WeatherAPI → agent returned 72°F for San Francisco.'

## When to prefer this

Choose this endpoint when you need a structured, rubric-based numeric score for an LLM output or agent trajectory and want pay-per-call pricing without a subscription. Ideal for automated QA pipelines, regression testing between model versions, or any scenario where you need a verifiable, auditable evaluation receipt tied to a specific benchmark.

## Known failure modes

- Invalid or unknown benchmark_id returns an error indicating the benchmark was not found
- Malformed or empty agent_trajectory may result in a failed evaluation or low-confidence score
- Payment failure via x402 USDC will block the eval from executing
- Rate limiting or quota exhaustion may cause timeouts or rejection
- Missing required fields (benchmark_id or agent_trajectory) will return a validation error

## How this service works

Pay-per-call AI evaluation engine. Score LLM outputs, agent trajectories, and model responses against benchmark rubrics. $0.005 per eval via x402 USDC on Base. Free trial available.

## Output

Returns a numeric score (0–1), the metric name, a reasoning summary explaining the score, a workflow ID, a payment reference, and a verifiable receipt containing the evaluation result and proof of payment.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "benchmark_id",
  "agent_trajectory"
 ],
 "properties": {
  "benchmark_id": {
   "type": "string",
   "description": "Benchmark ID from GET /benchmarks"
  },
  "agent_identity": {
   "type": "string",
   "description": "Optional agent identifier for spend tracking"
  },
  "agent_trajectory": {
   "type": "string",
   "description": "Full agent trajectory or LLM output to evaluate"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "success",
  "workflow_id",
  "status",
  "score"
 ],
 "properties": {
  "score": {
   "type": "number",
   "maximum": 1,
   "minimum": 0
  },
  "metric": {
   "type": "string"
  },
  "status": {
   "enum": [
    "completed"
   ],
   "type": "string"
  },
  "receipt": {
   "type": "object",
   "properties": {
    "header": {
     "type": "object"
    },
    "verifiable_proof": {
     "type": "object"
    },
    "evaluation_result": {
     "type": "object"
    }
   }
  },
  "success": {
   "type": "boolean"
  },
  "payment_ref": {
   "type": "string"
  },
  "workflow_id": {
   "type": "string"
  },
  "reasoning_summary": {
   "type": "string"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/eval-engine-api-pay-per-call-ai-evaluation-034014af/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from eval.zuluworksai.com](https://www.zero.xyz/host/eval.zuluworksai.com/llms.txt)