# Tereno x402 Endpoint Assurance

> Tereno x402 Endpoint Assurance is a paid API for AI agents from www.tereno.xyz, paid per call via x402, $0.03/call, status unknown (last checked 2026-09-14).

Probe and validate a third-party x402 endpoint's 402 challenge conformance, schema quality, availability history, and field-level changes since last observation without paying it.

## Facts

- Endpoint: POST https://www.tereno.xyz/api/v1/x402/assurance/invoke
- Price: $0.03/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/tereno-x402-endpoint-assurance-fc2ae536
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_bzpTAVdKqpNlLzuEqz_2R

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 tereno-x402-endpoint-assurance-fc2ae536 -d '<json body>'
```

Example prompt: Check whether the x402 endpoint at https://api.example.com/data is properly implementing its 402 challenge — I want to see its price, payTo address, network, and whether its schema quality and facilitator limit would actually allow settlement, without paying it.

## When to prefer this

Use this endpoint when you need to validate a third-party x402 endpoint's protocol conformance, monitor it for drift, or audit its challenge fields without incurring a payment. Prefer it over manual inspection when you need availability history, automated schema quality scoring, facilitator-limit risk detection, or Base claim recomputation from a held response. It is the right choice any time you want assurance about an x402 endpoint's correctness before committing funds or building an integration against it.

## Known failure modes

- Target URL is unreachable or returns non-402 status unexpectedly
- x402 challenge response is malformed and cannot be parsed
- Facilitator limit check cannot be evaluated without sufficient description metadata
- Blockchain claim recomputation fails if Base RPC is congested or address is invalid
- Request times out if the target endpoint is slow to respond
- Invalid method enum value causes input validation error

## How this service works

Verify and monitor a third-party x402 endpoint without paying it. Probe the live 402 challenge and check conformance: price, payTo, network, scheme, schema and example quality, whether its own advertised input still reaches a challenge, and whether its description fits the facilitator limit that silently blocks settlement. Then get availability history and a field-level diff since the last observation. Optional recomputation against Base.

## Output

Returns a conformance report covering the live 402 challenge fields (price, payTo, network, scheme), schema and example quality assessment, whether the endpoint's own advertised input triggers a 402, whether the description fits within facilitator settlement limits, availability history, and a field-level diff versus the last recorded observation. If an observed response and claims are supplied, also returns recomputed blockchain claim verdicts against Base.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "body": {
   "type": "object",
   "description": "JSON body to send with the probe, for POST resources."
  },
  "query": {
   "type": "object",
   "description": "Query parameters to send with the probe."
  },
  "claims": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "kind"
    ],
    "properties": {
     "kind": {
      "enum": [
       "erc20.symbol",
       "erc20.decimals",
       "erc20.totalSupply",
       "erc20.balanceOf",
       "native.balance",
       "contract.hasCode",
       "gas.priceGwei"
      ]
     },
     "owner": {
      "type": "string"
     },
     "token": {
      "type": "string"
     },
     "address": {
      "type": "string"
     },
     "tolerancePct": {
      "type": "number"
     }
    }
   },
   "description": "What to recompute out of observedResponse. Supported kinds: erc20.symbol, erc20.decimals, erc20.totalSupply, erc20.balanceOf, native.balance, contract.hasCode, gas.priceGwei."
  },
  "method": {
   "enum": [
    "GET",
    "POST"
   ],
   "description": "How that endpoint is normally called. Defaults to GET."
  },
  "resource": {
   "type": "string",
   "description": "Absolute HTTPS URL of the x402 endpoint to measure."
  },
  "observedResponse": {
   "type": "object",
   "description": "A paid response you already hold from that endpoint. Supply it to have its claims recomputed against Base."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/tereno-x402-endpoint-assurance-fc2ae536/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from www.tereno.xyz](https://www.zero.xyz/host/www.tereno.xyz/llms.txt)