# PreFlight Transaction Pre-Sign Safety Checker

> PreFlight Transaction Pre-Sign Safety Checker is a paid API for AI agents from meryol-agenticmarket-x402.hf.space, paid per call via x402, $0.015/call, status unknown (last checked 2026-09-13).

Analyzes EVM transaction calldata before signing to detect risk flags, decode intent, and recommend whether to approve or decline

## Facts

- Endpoint: POST https://meryol-agenticmarket-x402.hf.space/tx/explain
- Price: $0.015/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/preflight-transaction-pre-sign-safety-checker-1ec8777a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_xuL5NaESIYkI64UohFRxE

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 preflight-transaction-pre-sign-safety-checker-1ec8777a -d '<json body>'
```

Example prompt: Before I sign this transaction, check if it's safe — it's an approve() call to 0xabc... on Base with calldata 0x095ea7b3... and I want to know the risk flags, what it actually does, and whether I should decline it.

## When to prefer this

Use this endpoint when an AI agent or wallet needs to evaluate the safety of an EVM transaction BEFORE signing — especially for token approvals, bridge calls, or unfamiliar contract interactions. Prefer this over generic contract explorers when you need a structured risk verdict with actionable recommended_action and decoded argument context, not just ABI decoding.

## Known failure modes

- Unrecognized or non-standard calldata selector returns null decoded_args
- Contract not verified on-chain yields limited context and higher uncertainty
- Unsupported chain returns an error (only Ethereum, Base, Arbitrum, Optimism supported)
- Malformed or truncated calldata may produce incomplete decoding
- Rate limiting or payment failure returns HTTP 402 or 429

## How this service works

Pre-trade & pre-sign checks for autonomous agents: everything an agent verifies BEFORE signing a transaction — token due diligence, calldata red-flag decoding, oracle freshness, holder concentration, bridge routing with executable calldata, cross-venue perp funding, gas and price sanity checks. EVM chains: Ethereum, Base, Arbitrum, Optimism.

## Output

A JSON object containing the decoded function selector and signature, a plain-English explanation of what the transaction does, a list of specific risk flags (e.g. unlimited_token_approval, approval_to_unverified_contract), an overall verdict (e.g. 'danger'), a recommended action (e.g. 'decline'), and the target contract address and chain.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "chain",
      "to",
      "data"
     ],
     "properties": {
      "to": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$"
      },
      "data": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]+$"
      },
      "chain": {
       "enum": [
        "ethereum",
        "base",
        "arbitrum",
        "optimism"
       ],
       "type": "string"
      },
      "value": {
       "type": "string"
      }
     }
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST",
      "PUT",
      "PATCH"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "verdict",
      "explanation"
     ]
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "to": "0xabc...",
  "chain": "base",
  "notes": [],
  "verdict": "danger",
  "selector": "0x095ea7b3",
  "signature": "approve(address,uint256)",
  "risk_flags": [
   "unlimited_token_approval",
   "approval_to_unverified_contract"
  ],
  "explanation": "This grants type(uint256).max allowance on USDC to 0xabc... which is not source-verified. Common drainer pattern.",
  "decoded_args": null,
  "what_it_does": "Approve unlimited USDC spend by an unverified router.",
  "recommended_action": "decline"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/preflight-transaction-pre-sign-safety-checker-1ec8777a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from meryol-agenticmarket-x402.hf.space](https://www.zero.xyz/host/meryol-agenticmarket-x402.hf.space/llms.txt)