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x402-audit Calldata Encoder
x402
x402-audit Calldata Encoder is a paid API for AI agents from x402-audit.tatschluizguilherme.workers.dev, paid per call via x402, $0.1/call, status unknown (last checked 2026-10-03).
Encodes EVM function calls (by name or 4-byte selector + JSON arguments) into raw ABI-encoded calldata hex, with built-in round-trip decode verification, requiring no RPC or API key.
Price / call$0.1
Success—
StatusUnknown
How this service works
Pay-per-call on-chain API for AI agents and developers: wallet audits, token safety audits (honeypot detection), live gas prices, token prices, transaction receipts, balances, ENS resolution, block data, ERC-20 allowances, transaction simulation, swap quotes and multicall batches — all computed on-chain via public RPCs (no external market API). Pay per request in USDC on Base via the x402 exact scheme (EIP-3009 transferWithAuthorization). No API key, no signup, no subscription.
Output
Returns a JSON object containing the raw ABI-encoded calldata hex string ready to use in a transaction, the 4-byte function selector, and a 'verify' field showing the decoded round-trip interpretation of the calldata (function name and resolved argument values) so the caller can confirm correctness before signing. No RPC connection or API key is required.
Example use cases
Prepare ERC-20 approve calldata
“Encode calldata for the 'approve' function with spender 0xDef...5678 and amount 500000000 as JSON arguments, then show me the hex and the decoded round-trip verification so I know exactly what I'm signing.”
Build swap calldata for a DEX trade
“I need the raw calldata hex for a 'swapExactTokensForTokens' call — amountIn 1000000, amountOutMin 990000, path [0xToken1, 0xToken2], to 0xMyWallet, deadline 9999999999 — give me the encoded hex and show me the verify output so I can double-check it.”
Encode multicall transaction payload
“Can you encode a 'multicall' function call with a positional array of two encoded sub-calls as bytes, and return the full calldata hex with the embedded round-trip decode so I can verify what the multicall will execute?”
Technical details
Endpoint
GEThttps://x402-audit.tatschluizguilherme.workers.dev/encode?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to construct raw EVM calldata offline (no RPC, no blockchain access) for any of the ~40 common DeFi/ERC-20 functions, especially when you want immediate built-in verification via the round-trip decode. Prefer it over manual ABI encoding libraries when operating in an environment without Web3 tooling, or when you want a single HTTP call that both encodes and verifies correctness. Not suitable for arbitrary custom contract ABIs outside the built-in dictionary.
Side effects
- Unknown function name not in the ~40-function dictionary returns an error — use the 4-byte selector instead
- Malformed JSON arguments (wrong types, missing required fields) return an encoding error
- Passing an invalid or unrecognized 4-byte selector with no matching ABI entry may fail or return partial data
- Providing positional array arguments in wrong order causes silent mis-encoding — round-trip verify field helps catch this
- Network errors to the Cloudflare Worker edge node may cause timeouts
Output
Schema · Response
{
"type": "json",
"example": {
"fn": "transfer",
"args": {
"to": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"value": "1000000"
},
"verify": {
"args": [
"0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"1000000"
],
"name": "transfer",
"known": true,
"nested": null,
"argsNamed": {
"to": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
"value": "1000000"
},
"signature": "transfer(address,uint256)",
"decodeError": false
},
"network": "offline",
"calldata": "0xa9059cbb000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa9604500000000000000000000000000000000000000000000000000000000000f4240",
"selector": "0xa9059cbb",
"inputSize": 68,
"signature": "transfer(address to, uint256 value)",
"requestedAt": "2026-08-05T09:00:00.000Z"
}
}Tags
x402
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