# FastX402 Lab ERC-20 Calldata Decoder

> FastX402 Lab ERC-20 Calldata Decoder is a paid API for AI agents from fastx402.tools, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-17).

Decodes ERC-20 transfer, approve, and transferFrom calldata hex into human-readable function name, checksummed addresses, and token amounts

## Facts

- Endpoint: GET https://fastx402.tools/erc20-calldata-decode?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastx402-lab-erc-20-calldata-decoder-85f84b23
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_U1Pp9YpsDjO2ESyUUuMTa

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 fastx402-lab-erc-20-calldata-decoder-85f84b23
```

Example prompt: Before I sign this transaction, decode this calldata and tell me exactly what it does — who the recipient is and how many tokens are being transferred: 0xa9059cbb000000000000000000000000fb6916095ca1df60bb79ce92ce3ea74c37c5d3590000000000000000000000000000000000000000000000000000000000016e360

## When to prefer this

Use this endpoint when an AI agent or user needs to verify what an ERC-20 transaction calldata actually does before signing or broadcasting it — particularly for safety checks in wallet automation, DeFi interactions, or any agentic workflow that programmatically constructs or receives Ethereum transactions. Prefer this over manual ABI decoding when you need a lightweight, pay-per-call approach without running a full Ethereum node or ABI library.

## Known failure modes

- Unrecognized function selector (not transfer/approve/transferFrom) returns an error or null
- Malformed or truncated calldata causes a parse error
- Missing 0x prefix on input data may cause rejection
- Non-ERC-20 calldata (e.g. ETH transfers, other contract calls) will not decode correctly

## How this service works

146 pay-per-call tools for AI agents, from $0.001 per request in USDC on Base or Solana with x402. No account, no API key.

## Output

A JSON object containing the decoded ERC-20 function name (e.g. 'transfer', 'approve', 'transferFrom'), the 4-byte function selector (e.g. '0xa9059cbb'), and an args object with checksummed Ethereum addresses (to, from, spender) and the exact token amount as a string integer.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "data"
     ],
     "properties": {
      "data": {
       "type": "string",
       "description": "Transaction calldata, 0x + hex"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "args": {
       "type": "object",
       "properties": {
        "to": {
         "type": "string"
        },
        "amount": {
         "type": "string"
        }
       }
      },
      "function": {
       "type": "string"
      },
      "selector": {
       "type": "string"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "args": {
   "to": "0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359",
   "amount": "1500000"
  },
  "function": "transfer",
  "selector": "0xa9059cbb"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastx402-lab-erc-20-calldata-decoder-85f84b23/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fastx402.tools](https://www.zero.xyz/host/fastx402.tools/llms.txt)