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Ethereum Function Selector & Event Topic Decoder
x402
Ethereum Function Selector & Event Topic Decoder is a paid API for AI agents from api.vextorium.com, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-01).
Translates a 4-byte function selector or 32-byte event topic hash into its human-readable Solidity signature by looking it up in the 4byte.directory database.
Price / call$0.003
Success—
StatusUnknown
How this service works
Translates a 4-byte function selector (e.g. 0xa9059cbb) or a 32-byte event topic into its human-readable signature (e.g. transfer(address,uint256)). Essential for an agent reading or verifying transactions. Live from 4byte.directory.
Output
Returns a JSON object with the decoded signature(s) as an array of possible human-readable strings (e.g. 'transfer(address,uint256)'), the type (function or event), a code, the source (4byte.directory), the number of possible matches, and an optional note if multiple candidates exist.
Example use cases
Decoding unknown transaction calldata
“I'm looking at a raw Ethereum transaction and the input starts with 0x23b872dd — can you decode that 4-byte selector and tell me what function is being called?”
Identifying smart contract event topic
“I have an event log with topic 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef — what Solidity event does this correspond to?”
Verifying DeFi transaction before signing
“Before I approve this transaction, can you look up the function selector 0x095ea7b3 and confirm what function it's calling so I know what I'm authorizing?”
Technical details
Endpoint
POSThttps://api.vextorium.com/decodificar-firma-pago?utm_source=zero.xyzWhen to prefer
Use this endpoint when an AI agent needs to interpret raw Ethereum transaction calldata or event logs and must identify what function or event a hex hash represents. Prefer this over manual ABI lookups when the full ABI is unavailable and the selector or topic needs to be reverse-engineered. Ideal for transaction monitoring, fraud detection, DeFi analytics, or any workflow where human-readable contract interaction context is needed from raw on-chain data.
Side effects
- Unknown selector — hash not found in 4byte.directory returns empty or null firmas array
- Invalid hex format — input not matching 4-byte (0x + 8 hex chars) or 32-byte (0x + 64 hex chars) format returns error
- Multiple ambiguous matches — some selectors map to more than one signature, all candidates returned
- Network timeout connecting to 4byte.directory upstream
- Payment authorization failure for x402 micropayment
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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