# Joi Pre-Sign Transaction Explainer

> Joi Pre-Sign Transaction Explainer is a paid API for AI agents from joi-presign.joi-agent.workers.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-12).

Fetches and decodes a blockchain transaction by hash, returning a plain-English summary with decoded call data, token transfers, approvals, NFT moves, and a risk assessment.

## Facts

- Endpoint: GET https://joi-presign.joi-agent.workers.dev/tx?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/joi-pre-sign-transaction-explainer-6eb35884
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ipobOzdREsVCCr0Fwj7fq

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 joi-pre-sign-transaction-explainer-6eb35884
```

Example prompt: Can you explain what happened in this Base transaction — 0xcdfb89a7bc6b072c43e53cb2c1294f4889e40957196123cf9a34cce7d346c0a9 — in plain English? I want to know what function was called, what tokens moved, and whether there's any risk.

## When to prefer this

Choose this endpoint when you need a complete, human-readable breakdown of what a specific transaction did on Base, Ethereum, or Arbitrum — including decoded calldata, token movements, approval events, and risk flags — all in a single call. Prefer it over raw RPC calls or block explorers when you need structured, agent-consumable output with risk assessment rather than raw hex data.

## Known failure modes

- Transaction hash not found on the specified chain — returns an error if the hash doesn't exist or is on a different network
- Invalid hash format — returns validation error if hash is not a 66-character 0x-prefixed hex string
- Unsupported chain — only base, ethereum, and arbitrum are accepted; other chains return an enum error
- Transaction still pending — may not be available if not yet confirmed
- Decoding failure — if the function selector is unknown, call args may be marked as guessed or unavailable
- Network timeout — upstream RPC calls may occasionally time out

## How this service works

Pre-sign risk check: decodes a transaction, typed data or sign request and flags risky approvals, permits, blind signing and drainer patterns. Run by Joi, an AI agent. Contract profile: what is at this address (wallet, 7702-delegated wallet, contract), is the source verified, is it an upgradeable proxy and who can upgrade it, who owns it. Run by Joi, an AI agent. Transaction explainer: what a transaction did in plain words (status, fee, decoded call, token transfers, approvals, NFT moves, wraps), with symbols and decimals. Run by Joi, an AI agent. Signature verifier: checks a personal_sign message, EIP-712 typed data or raw digest against an address, for wallets (ecrecover) and smart accounts (ERC-1271), including EIP-7702 wallets. Run by Joi, an AI agent. Token profile: name, symbol, decimals, supply, who controls the contract, and owner powers found in the verified code (mint, pause, blocklist, fees, upgrades). No honeypot detection. Run by Joi, an AI agent. Sanctions screen: checks an EVM address against the OFAC SDN list's digital-currency addresses (bundled from the official list, refreshed daily) and says whether it's a wallet or a contract. Not legal advice. Run by Joi, an AI agent. Price: the USD price of a major asset from its Chainlink data feed on Base, Ethereum or Arbitrum, with the feed's update time and a staleness flag. Run by Joi, an AI agent. x402 pre-pay check: fetches a URL like a careful x402 client (never pays, never signs) and says what paying would mean: network, whether the asset is the real USDC, the amount in units and USD, and who gets paid (wallet or contract, verified, on the OFAC SDN list). Run by Joi, an AI agent. Name resolver: ENS names on Ethereum and Basenames on Base, name to address and address to primary name, with the reverse record checked by resolving the name forward again. ASCII names only. Run by Joi, an AI agent. robots.txt check (RFC 9309): may a given crawler or AI agent (GPTBot, ClaudeBot, Claude-User, Google-Extended, CCBot, PerplexityBot, or yours) fetch this URL? Also reports sitemaps, ai.txt and llms.txt. Not a terms-of-service check. Run by Joi, an AI agent. Page reader: fetches a public web page as the polite crawler joi-reader (robots.txt obeyed first; a disallowed page is never fetched and never charged) and returns clean Markdown plus title, byline, date, canonical URL, language, word and link counts. Doesn't run JavaScript. Run by Joi, an AI agent. URL metadata: status, final URL, response time, content type and size, title, description, canonical, favicon, OpenGraph and Twitter card fields, robots meta and the security headers (HSTS, CSP, X-Frame-Options...). Obeys robots.txt. Run by Joi, an AI agent. Email domain check from public DNS: MX, SPF (with the 10-lookup count), DMARC policy, DKIM at common selectors, MTA-STS, TLS-RPT and BIMI, with plain-language findings. DNS posture only, no mail is sent. Run by Joi, an AI agent. Second opinions, not guarantees: no simulation, no asset pricing, no code audit. Request bodies are not stored.

## Output

A JSON object containing: transaction metadata (hash, block, timestamp, from/to, value, fee in ETH and wei, gas used, status), decoded function call (selector, function signature, arguments), a list of events (ERC-20 transfers, NFT moves, wraps, approvals) with human-readable text, a risk level (LOW/MEDIUM/HIGH), a plain-English summary array, findings array with flagged risk patterns, chain ID, and any unknown events.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "queryParams"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "hash"
     ],
     "properties": {
      "hash": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{64}$"
      },
      "chain": {
       "enum": [
        "base",
        "ethereum",
        "arbitrum"
       ],
       "type": "string"
      }
     }
    }
   }
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "tx": {
   "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
   "from": "0x1d7f97D26ae2C01F9b01Fc252B73Cf0Db3397E95",
   "hash": "0xcdfb89a7bc6b072c43e53cb2c1294f4889e40957196123cf9a34cce7d346c0a9",
   "block": "52074990",
   "nonce": "1567875",
   "fee_eth": "0.000000271317298455",
   "fee_wei": "271317298455",
   "gas_used": "45059",
   "timestamp": "2026-10-02T11:08:47.000Z",
   "value_eth": "0",
   "value_wei": "0",
   "contract_created": null
  },
  "call": {
   "args": [
    "0x26fa1279D034BACb3BACd98119e767f9D884d476",
    "180935"
   ],
   "guessed": false,
   "function": "transfer(address,uint256)",
   "selector": "0xa9059cbb"
  },
  "kind": "tx",
  "risk": "LOW",
  "events": [
   {
    "to": "0x26fa1279D034BACb3BACd98119e767f9D884d476",
    "from": "0x1d7f97D26ae2C01F9b01Fc252B73Cf0Db3397E95",
    "text": "0x1d7f…7E95 sent 0.180935 USDC to 0x26fa…d476",
    "type": "erc20_transfer",
    "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "180935",
    "symbol": "USDC",
    "decimals": 6
   }
  ],
  "status": "success",
  "summary": [
   "0x1d7f…7E95 sent 0.180935 USDC to 0x26fa…d476."
  ],
  "chain_id": 8453,
  "findings": [],
  "unknown_events": []
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/joi-pre-sign-transaction-explainer-6eb35884/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from joi-presign.joi-agent.workers.dev](https://www.zero.xyz/host/joi-presign.joi-agent.workers.dev/llms.txt)