# Agent Capability Index & API Discoverability Pre-Payment Check

> Agent Capability Index & API Discoverability Pre-Payment Check 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 2026-10-23).

Runs a structured decision procedure to verify that a discovered API capability is real, indexed, and safe to pay before an agent authorizes settlement

## Facts

- Endpoint: GET https://k2so-8080.on.ascii.dev/api/services/agent-capability-index-api-discoverability-for-a?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-23
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-capability-index-api-discoverability-pre-payment-check-e5f3bbd9
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_XUMfEXDcDR3ONm7XaFe0L

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 agent-capability-index-api-discoverability-pre-payment-check-e5f3bbd9
```

Example prompt: Before you pay for that capability we found in the agentic.market catalog, run the pre-payment check on it — verify the endpoint actually responds and the claimed function matches what's listed, so we don't waste USDC on a stub or a bad listing.

## When to prefer this

Use this endpoint when an AI agent has discovered a paid API capability from any source (well-known file, MCP server, capability registry, market catalog) and needs a structured go/no-go decision before authorizing any x402 or USDC settlement. Prefer this over ad-hoc checks when the discoverability source is bazaar, agentic.market, or a facilitator listing, where stub or fraudulent entries are possible.

## Known failure modes

- Endpoint returns 404/405 or tiny body indicating a stub — procedure flags as unsafe to pay
- Capability name mismatch between index entry and actual endpoint behavior — returns ok:false
- Endpoint unreachable or times out — resolution check fails
- Discoverability source unrecognized or untrusted — procedure cannot confirm indexing
- Payment challenge (402) absent and no documented auth — flagged as non-conformant

## How this service works

Decision procedure for an agent deciding whether a discovered API capability is real, indexed, and safe to pay before it authorizes settlement. Input: candidate endpoint or capability index entry, claimed tool/function name, price, discoverability source (well-known file, MCP server, capability registry, market catalog). Step 1 verify the index entry resolves: endpoint responds, 402 challenge or documented auth exists, no 404/405/tiny-body stub. Step 2 check capability match: claimed function

## Output

Returns a structured result with an 'ok' boolean, a 'brief' prose explanation of the decision procedure for the agent, the service slug, generation source (llm/reasoning/deterministic), an ISO-8601 timestamp, and payment metadata including payer and transaction details — giving the agent a clear go/no-go signal before settling.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "agent capability index and API discoverability gate: pre-payment check for agent paid response",
     "$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/agent-capability-index-api-discoverability-pre-payment-check-e5f3bbd9/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)