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OnchainExpat Contract Decoder API
x402
OnchainExpat Contract Decoder API is a paid API for AI agents from x402.onchainexpat.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-13).
Decodes and analyzes smart contract data, ABIs, or transaction calldata using pay-per-request x402 protocol
Price / call$0.02
Success—
StatusUnknown
How this service works
Pay-per-request AI, crypto, proxy, and utility APIs using x402 protocol
Output
Returns a JSON object with decoded smart contract data including function name, parameter names and values, ABI fragments, and human-readable interpretation of the calldata or contract interaction.
Example use cases
Monitor suspicious wallet transactions
“I'm seeing some weird transactions from a wallet I'm tracking. Can you decode what these contract calls are actually doing? I've got the raw calldata from a few transactions and need to understand if they're token transfers, swaps, or something else entirely.”
Audit smart contract interaction history
“I want to review all the function calls made to our contract over the past week. I have the transaction calldata from our logs, but it's all hex encoded. Can you decode each one and tell me what functions were called and with what parameters?”
Debug DeFi protocol integration issues
“Our app is calling a Uniswap contract, but something's going wrong. I have the calldata we're sending, but I need to verify it's actually structured correctly. Can you decode it and confirm the function name and all the parameters match what we intended?”
Technical details
Endpoint
POSThttps://x402.onchainexpat.com/api/x402-crypto/contract-decoderWhen to prefer
Use this endpoint when you need to decode raw EVM smart contract calldata, understand what a transaction is doing, or interpret contract interactions without setting up your own ABI parsing infrastructure. Ideal for pay-per-use blockchain data decoding without API key management.
Side effects
- Invalid or malformed calldata hex returns a parse error
- Unknown contract ABI with no verified source may return incomplete decoding
- Unsupported blockchain network returns an error
- Missing required input fields returns a 400 validation error
- Payment not received via x402 protocol returns 402 Payment Required
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| chain | string | Blockchain (default: base) |
| addressrequired | string | Contract address (0x + 40 hex chars) |
Output
Schema · Response
| Field | Type | Description |
|---|---|---|
| data | object | |
| success | boolean |
Tags
x402
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