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FastX402 Lab ERC-20 Calldata Decoder
x402
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
Price / call$0.002
Success—
StatusUnknown
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.
Example use cases
Pre-signing transaction safety check
“I'm about to sign this ERC-20 transaction but I want to verify what it actually does before I approve it — can you decode this calldata for me: 0xa9059cbb000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045000000000000000000000000000000000000000000000000016345785d8a0000”
Verify approve allowance before DeFi interaction
“My DeFi app is asking me to approve a token spend — can you decode this calldata and tell me which address is getting approved and for exactly how much: 0x095ea7b3000000000000000000000000uniswap_router_address0000000000000000000000000000000000000000000000000de0b6b3a7640000”
Audit agent-generated transaction calldata
“My AI trading agent generated this calldata for a transferFrom call — decode it and tell me the exact sender, recipient, and amount so I can double-check it matches the intended trade: 0x23b872dd000000000000000000000000abc123sender000000000000000000000000def456recipient000000000000000000000000000000000000000000000000002386f26fc10000”
Technical details
Endpoint
GEThttps://fastx402.tools/erc20-calldata-decode?utm_source=zero.xyzWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"args": {
"to": "0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359",
"amount": "1500000"
},
"function": "transfer",
"selector": "0xa9059cbb"
}
}Tags
x402
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