# Chain Evidence Check

> Chain Evidence Check is a paid API for AI agents from api.aiskills402.com, paid per call via x402, $0.05/call, status unknown (last checked 2026-11-01).

Judges whether an on-chain observation (transaction receipt, block, balance, RPC response) truly proves a specific claim about a payment, wallet, or EVM RPC endpoint, returning a binary verdict with reasoning.

## Facts

- Endpoint: GET https://api.aiskills402.com/v1/skills/chain-evidence-check/file?utm_source=zero.xyz
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-11-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/chain-evidence-check-1474820d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_-_dP8MsMiO3Xh3lkKPMBd

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 chain-evidence-check-1474820d
```

Example prompt: I just got a null transaction receipt two seconds after my USDC payment settled on Base — can you check whether that actually proves the payment failed, or if it's just a timing issue with the RPC endpoint?

## When to prefer this

Choose this endpoint when an AI agent or developer needs to reason about whether a specific on-chain data point (receipt, balance, explorer response) is actually sufficient evidence for a claim — especially in x402 payment flows, automated settlement verification, or when debugging false-negative payment proofs on EVM chains. It is purpose-built for the specific failure modes of EVM evidence interpretation (timing lags, RPC errors, indexer delays) rather than generic blockchain analytics.

## Known failure modes

- Ambiguous or incomplete observation description may result in an inconclusive verdict
- RPC endpoints that refuse receipts with errors may not provide enough data for a definitive judgment
- Payment via x402 required — unpaid requests will return a 402 response
- Highly novel chain configurations or non-standard EVM forks may fall outside the model's training
- Edge cases involving simultaneous chain reorganizations may produce uncertain verdicts

## How this service works

Chain Evidence Check — Judges whether an on-chain observation really proves a claim about a payment, a wallet or an RPC endpoint on an EVM chain, and answers as JSON with a binary verdict, the reason and the one check that would decide. Knows the readings that answer for the wrong thing - a null transaction receipt seconds after settlement, a block explorer that indexes a minute late and a balance view that lags its own transfer list, a public RPC endpoint that refuses receipts with an error or…

## Output

A JSON object with a binary verdict (true/false), a plain-language reason explaining the judgment, and identification of the single decisive check that would confirm or refute the claim. The response also includes the SKILL.md content, a sha256 hash, settlement transaction reference, and a redownload token for future access.

## 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"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "file": {
   "name": "SKILL.md",
   "content": "<the SKILL.md file>",
   "encoding": "utf-8"
  },
  "name": "Chain Evidence Check",
  "skill": "chain-evidence-check",
  "sha256": "<sha256 of SKILL.md>",
  "receipt": {
   "tx": "0x<settlement transaction>",
   "settled": true
  },
  "version": "1.0.0",
  "redownload": {
   "url": "<api>/v1/purchases/<token>",
   "token": "<64 hex chars>"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/chain-evidence-check-1474820d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.aiskills402.com](https://www.zero.xyz/host/api.aiskills402.com/llms.txt)