# OBOL EVM Calldata Guard — Pre-Sign Safety Verdict

> OBOL EVM Calldata Guard — Pre-Sign Safety Verdict is a paid API for AI agents from obol-x402.fly.dev, paid per call via x402, $0.05/call, status down (last checked 2026-09-15).

Decodes and audits raw EVM transaction calldata before signing, flagging unlimited approvals, drain-in-multicall, and setApprovalForAll attacks with a signed BLOCK/ALLOW policy verdict.

## Facts

- Endpoint: GET https://obol-x402.fly.dev/v1/evm/guard
- Price: $0.05/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/obol-evm-calldata-guard-pre-sign-safety-verdict-b0c8fafa
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_HBsWYYvOtykh5AfGnzKuw

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 obol-evm-calldata-guard-pre-sign-safety-verdict-b0c8fafa
```

Example prompt: Before I sign this transaction, run a calldata guard check on this hex data and tell me if it's trying to set an unlimited approval or drain my wallet — I need a BLOCK or ALLOW verdict with the decoded function details.

## When to prefer this

Choose this endpoint when an AI agent needs to validate raw EVM transaction calldata before signing — specifically to catch unlimited approvals, setApprovalForAll, or multicall drains. Unlike generic RPC simulation, OBOL returns a structured, Ed25519-signed BLOCK/ALLOW verdict designed for autonomous agent consumption. Prefer this over manual ABI decoding or simulation-only tools when you need a definitive, auditable policy decision rather than just a trace.

## Known failure modes

- Malformed or non-decodable calldata returns a parse error
- Unsupported chain or contract ABI yields incomplete decoded output
- Payment not included or insufficient USDC triggers 402 Payment Required
- Network timeout on fly.dev host returns 503
- Calldata for a novel proxy pattern may not decode fully, reducing flag accuracy

## How this service works

Pre-trade safety for AI agents on Base, Ethereum, Arbitrum, Optimism, Polygon, BNB and Robinhood Chain. Is this token a rug — and can I sell it again? Signed verdicts before you buy, approve, send or sign: token rug/honeypot check with buy-sell tax, honeypot sell-simulation, pre-sign calldata guard (unlimited-approve / setApprovalForAll / drain-in-multicall), wallet risk with sanctions screening, tx preflight, and a launch feed with safety overlays. Plus unique Bitcoin forensics no RPC gives you: money-graph role, whale and exchange fingerprinting, Satoshi-era provenance, validation-gated block anomalies, and broadcast-fee timing. Every response Ed25519-signed and independently verifiable. Pay-per-call USDC on Base — no keys, no accounts, no signup. Free: /catalog, /llms.txt, and a preview for every paid SKU.

## Output

A JSON object containing a 'policy' field (BLOCK or ALLOW), an array of 'flags' each with a flag name and severity level (e.g. critical), and a 'decoded' array breaking down the calldata into human-readable function name, spender address, and amount. The entire response is Ed25519-signed for independent verifiability. Costs $0.05 USDC per call via x402 on Base.

## 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",
     "required": [
      "to",
      "data"
     ],
     "properties": {
      "to": {
       "type": "string",
       "description": "0x contract being called"
      },
      "data": {
       "type": "string",
       "description": "0x calldata to decode"
      },
      "from": {
       "type": "string"
      },
      "chain": {
       "enum": [
        "base",
        "ethereum",
        "arbitrum",
        "optimism",
        "polygon",
        "bnb",
        "robinhood"
       ],
       "type": "string",
       "default": "base"
      },
      "value": {
       "type": "string"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "flags": [
   {
    "flag": "unlimited_approval",
    "level": "critical"
   }
  ],
  "guard": "pre-sign calldata decode",
  "policy": "BLOCK",
  "decoded": [
   {
    "amount": "UNLIMITED",
    "spender": "0x…",
    "function": "approve(address,uint256)"
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/obol-evm-calldata-guard-pre-sign-safety-verdict-b0c8fafa/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from obol-x402.fly.dev](https://www.zero.xyz/host/obol-x402.fly.dev/llms.txt)