# x402 Merchant Endpoint Pre-Payment Vetting Standard

> x402 Merchant Endpoint Pre-Payment Vetting Standard is a paid API for AI agents from k2so-8080.on.ascii.dev, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-11).

Returns a structured decision procedure for assessing an HTTP 402 merchant endpoint's operational health before spending USDC via x402.

## Facts

- Endpoint: GET https://k2so-8080.on.ascii.dev/api/services/x402-merchant-endpoint-pre-payment-vetting-stand?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-merchant-endpoint-pre-payment-vetting-standard-525e7c4f
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_D13IiFNvhGzklZT84dnLn

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 x402-merchant-endpoint-pre-payment-vetting-standard-525e7c4f
```

Example prompt: Before my agent pays that x402 endpoint, give me the full decision procedure for vetting its operational health — check whether the WWW-Authenticate challenge is correct, whether the quoted price matches what was advertised, and what settlement finality evidence to look for.

## When to prefer this

Choose this endpoint when an autonomous agent needs a structured, blunt decision procedure for vetting x402 merchant endpoints before committing USDC — especially when building payment safety logic, evaluating unfamiliar 402-gated APIs, or implementing pre-payment health checks in an agentic workflow. Prefer this over generic API health-check tools when the concern is specifically x402 payment challenge correctness, price honesty, and settlement finality.

## Known failure modes

- Payment not included — endpoint returns HTTP 402 requiring $0.002 USDC before content is delivered
- Invalid or missing 'input' object in request body returns schema validation error
- Topic override not recognized returns a generic x402 vetting procedure rather than topic-specific guidance
- LLM/reasoning backend unavailable returns ok=false with error detail in result
- Slow upstream generation may exceed agent latency budgets for real-time workflows

## How this service works

Paid agent-facing brief on x402 merchant endpoint pre-payment vetting standard: how to assess an HTTP 402 endpoint's operational health before spending USDC. Checks: WWW-Authenticate Payment challenge contract presence and correctness, price honesty (advertised vs quoted), latency budget, response schema quality, settlement finality evidence, fallback to alternate merchants. · Build a decision procedure or schema for: x402. Blunt decision procedure, not marketing.

## Output

A paid JSON response containing a 'brief' field with decision procedure prose and a 'procedure' field outlining the concrete vetting steps an agent should execute before paying an x402 endpoint. Includes metadata like generation source (llm/reasoning/deterministic), model used, topic, and ISO-8601 timestamp. The procedure covers: WWW-Authenticate Payment challenge validation, advertised-vs-quoted price honesty, latency budget assessment, response schema quality, settlement finality evidence, and fallback merchant logic.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "x402 merchant endpoint pre-payment vetting standard: how to assess an paid response",
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "required": [
      "ok",
      "paid",
      "service",
      "provider",
      "result"
     ],
     "properties": {
      "ok": {
       "type": "boolean"
      },
      "paid": {
       "type": "boolean"
      },
      "result": {
       "type": "object",
       "required": [
        "ok",
        "service"
       ],
       "properties": {
        "ok": {
         "type": "boolean",
         "description": "Handler success"
        },
        "brief": {
         "type": "string",
         "description": "Decision procedure prose for agents"
        },
        "model": {
         "type": "string"
        },
        "topic": {
         "type": "string"
        },
        "service": {
         "type": "string",
         "description": "Service slug"
        },
        "procedure": {
         "type": "string"
        },
        "generatedAt": {
         "type": "string",
         "description": "ISO-8601 timestamp"
        },
        "generationSource": {
         "enum": [
          "llm",
          "reasoning",
          "deterministic"
         ],
         "type": "string"
        }
       }
      },
      "payment": {
       "type": "object",
       "properties": {
        "code": {
         "type": "string"
        },
        "payer": {
         "type": "string"
        },
        "detail": {
         "
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-merchant-endpoint-pre-payment-vetting-standard-525e7c4f/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from k2so-8080.on.ascii.dev](https://www.zero.xyz/host/k2so-8080.on.ascii.dev/llms.txt)