{"uid":"cap_p4U6NyeKkunVyy6Wmcwd9","slug":"ethereum-selector-event-topic-hash-lookup-e2d67055","name":"Ethereum Selector / Event Topic Hash Lookup","description":"Resolve a 4-byte function selector or a 32-byte event topic hash to its known human-readable Solidity signatures, via the openchain.xyz signature database with 4byte.directory as fallback. Unknown selectors return {found:false} with an empty list, not an error.","url":"https://agent402.tools/api/selector-lookup","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"selector":{"type":"string","description":"0x-prefixed 4-byte function selector (10 chars) or 32-byte event topic hash (66 chars)."}}},"responseSchema":{"type":"json","example":{"kind":"function","found":true,"source":"openchain.xyz","selector":"0xa9059cbb","signatures":["transfer(address,uint256)"]}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.002","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.002/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.002","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.002","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_Zvz6DG9th7sC--cumAZ7C","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.002","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Resolves a 4-byte Ethereum function selector or 32-byte event topic hash to its known human-readable Solidity signatures using openchain.xyz with 4byte.directory as fallback.","exampleAgentPrompt":"Can you look up what Solidity function the 4-byte selector 0xa9059cbb maps to? I'm trying to decode some Ethereum transaction calldata.","exampleUseCases":null,"resultDescription":"Returns an object indicating whether the selector was found (found: true/false) and a list of matching human-readable Solidity function or event signatures (e.g. 'transfer(address,uint256)'). Unknown selectors return {found: false} with an empty list.","failureModes":["Unknown selector returns {found: false} with empty signatures list — not an error, just not in the database","Invalid hex format or wrong length (not 10 chars for function selector or 66 chars for event topic) may return an error","Upstream openchain.xyz and 4byte.directory both unavailable causes lookup failure","Malformed 0x-prefix or non-hex characters cause validation failure"],"whenToPreferThis":"Use this endpoint when you need to decode raw Ethereum calldata or event logs by resolving 4-byte function selectors or 32-byte event topic hashes to human-readable Solidity signatures. Prefer this over manual ABI lookups when you don't have the contract's ABI on hand, or when debugging unknown contract interactions. It covers a broad corpus via openchain.xyz with 4byte.directory as fallback, maximizing match probability.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-09-15T01:07:57.894Z","isFirstParty":false}