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EVM Calldata Decoder
x402
EVM Calldata Decoder is a paid API for AI agents from agent402.tools, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-15).
Decodes EVM smart-contract transaction calldata into a human-readable function name and typed parameters using an ABI, function signature, or 4-byte selector lookup.
Price / call$0.003
Success—
StatusUnknown
How this service works
Decode EVM smart-contract transaction calldata into the function name and typed parameters. Supply an ABI (from /api/contract-abi) or a signature like transfer(address,uint256) for a fully offline decode; with neither, the 4-byte selector is resolved via the openchain.xyz signature database (4byte.directory fallback) and each candidate signature is tried. Unknown selectors return a documented partial decode (selector + raw 32-byte words) instead of an error.
Output
Returns the decoded function name and a list of typed, named parameters with their values extracted from the calldata, either using the provided ABI, the supplied function signature, or a 4-byte selector resolution from a public registry.
Example use cases
Example prompt
“Can you decode this calldata for me: 0xa9059cbb000000000000000000000000ab5801a7d398351b8be11c439e05c5b3259aec9000000000000000000000000000000000000000000000000016345785d8a0000 — use the function signature transfer(address,uint256) so we don't need the full ABI.”
Technical details
Endpoint
POSThttps://agent402.tools/api/calldata-decodeWhen to prefer
Use this endpoint when you have raw EVM transaction calldata (0x-prefixed hex) and need to understand what function is being called and with what arguments. Ideal for transaction analysis, debugging contract interactions, building block explorers, or auditing on-chain activity. Prefer this over manual decoding or etherscan lookups when you want a programmatic, offline-capable decode — especially if you already have the ABI or function signature.
Side effects
- Invalid or malformed calldata hex returns a parse error
- Unknown 4-byte selector with no ABI or signature provided results in an unresolvable decode error
- Calldata exceeding 100KB is rejected
- Mismatched ABI or signature causes parameter decoding to fail with a type mismatch error
- Malformed ABI JSON array causes an invalid input error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| abi | array | Optional contract ABI (JSON array) - enables a fully offline decode with parameter names. |
| data | string | 0x-prefixed calldata (selector + encoded args). Max 100KB. |
| signature | string | Optional function signature, e.g. transfer(address,uint256) - offline decode without a full ABI. |
Output
Schema · Response
{
"type": "json",
"example": {
"name": "transfer",
"params": [
{
"name": null,
"type": "address",
"value": "0xabf4fabd7c416fb67202e5f9002389fc75e2a9d0"
},
{
"name": null,
"type": "uint256",
"value": "1000000"
}
],
"source": "openchain.xyz",
"decoded": true,
"selector": "0xa9059cbb",
"signature": "transfer(address,uint256)"
}
}Tags
x402
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