# x402 Payment-Terms Health Validation & MCP Tool Cost Pre-Flight

> x402 Payment-Terms Health Validation & MCP Tool Cost Pre-Flight is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-10-30).

Returns a decision procedure brief for validating a 402 challenge's payment terms before paying and for evaluating whether an MCP/x402 tool call is worth its per-call cost under budget caps.

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/agent-facing-x402-payment-terms-health-validatio?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-payment-terms-health-validation-mcp-tool-cost-pre-flight-a3b6ecfd
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_v7sUkffr8sgBQjcETlTwf

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-payment-terms-health-validation-mcp-tool-cost-pre-flight-a3b6ecfd
```

Example prompt: Before I pay this 402 challenge, can you run a pre-flight check to confirm its payment terms are well-formed — valid scheme, amount, asset, network, timeout, and expiry — and tell me whether it's actually payable or just malformed?

## When to prefer this

Choose this endpoint when an AI agent needs a structured, blunt decision procedure for validating x402 payment challenges before spending — especially when distinguishing malformed challenges from legitimate ones, or when evaluating whether an MCP tool's unknown per-call cost is within acceptable budget bounds. Prefer this over general payment libraries when you need reasoned prose guidance rather than a simple pass/fail boolean.

## Known failure modes

- Malformed input object or missing required fields returns a validation error
- If the service is unavailable, no brief is generated
- LLM generation failure may result in an empty or partial brief field
- Ambiguous or missing topic parameter may yield a generic rather than targeted procedure
- Payment not completed results in a non-paid response without the full brief content

## How this service works

Paid agent-facing brief on agent-facing x402 payment-terms health validation and MCP tool cost pre-flight: a procedure for validating that a 402 challenge's payment terms are well-formed (WWW-Authenticate scheme, amount, asset, network, timeout, expiry) BEFORE paying, distinguishing up-but-malformed from up-and-payable, plus deciding whether an MCP/x402 tool call is worth its unknown per-call cost under budget caps. Distinc-0. Blunt decision procedure, not marketing.

## Output

A structured brief containing a decision procedure in prose form: whether the 402 challenge's payment terms are well-formed across all required fields (scheme, amount, asset, network, timeout, expiry), a clear verdict distinguishing up-but-malformed from up-and-payable, and guidance on whether an MCP/x402 tool call is worth its cost under budget constraints. Response includes ok/paid flags, service slug, provider, generation source, and ISO-8601 timestamp.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "agent-facing x402 payment-terms health validation and MCP tool cost pr paid response",
     "$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-payment-terms-health-validation-mcp-tool-cost-pre-flight-a3b6ecfd/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from k2so.wrong.systems](https://www.zero.xyz/host/k2so.wrong.systems/llms.txt)