{"uid":"cap_X3sRbbQy1WqtCY8vO8MG0","slug":"fastx402-solidity-selector-event-topic-calculator-84b478d7","name":"FastX402 Solidity Selector & Event Topic Calculator","description":"146 pay-per-call tools for AI agents, from $0.001 per request in USDC on Base or Solana with x402. No account, no API key.","url":"https://fastx402.tools/solidity-selector?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET"],"type":"string"},"queryParams":{"type":"object","required":["signature"],"properties":{"signature":{"type":"string","description":"Solidity function or event signature, e.g. transfer(address,uint256)"}}}},"additionalProperties":false},"output":{"type":"object","required":["type"],"properties":{"type":{"type":"string"},"example":{"type":"object","properties":{"topic":{"type":"string"},"selector":{"type":"string"},"signature":{"type":"string"}}}}}}},"responseSchema":{"type":"json","example":{"topic":"0xa9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b","selector":"0xa9059cbb","signature":"transfer(address,uint256)"}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.001","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":"$0.001/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_mpxOTWp0bKWYitgoXO1zJ","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.001","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Computes the 4-byte function selector and 32-byte event topic hash from a Solidity function or event signature string.","exampleAgentPrompt":"What's the 4-byte selector and 32-byte event topic for the Solidity signature transfer(address,uint256)?","exampleUseCases":[{"title":"Decode incoming smart contract calldata","prompt":"I'm seeing calldata that starts with 0xa9059cbb — can you confirm which Solidity function selector that corresponds to, and give me the full selector and topic hash for transfer(address,uint256)?"},{"title":"Build EVM log filter for an event","prompt":"I need to filter Ethereum logs for Transfer events. Can you give me the 32-byte event topic hash for Transfer(address,address,uint256) so I can use it in my eth_getLogs filter?"},{"title":"Verify ABI function selector before sending transaction","prompt":"Before I submit this transaction, can you compute the 4-byte function selector for approve(address,uint256) so I can double-check the calldata prefix is correct?"}],"resultDescription":"Returns a JSON object containing the original signature string, the 4-byte function selector (e.g. 0xa9059cbb), and the 32-byte event topic hash (e.g. 0xa9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b).","failureModes":["Missing or malformed signature query parameter returns an error","Signature with invalid Solidity syntax may return unexpected hash or error","Network timeout or service unavailability returns a non-200 response","Payment failure via x402 protocol blocks the request before processing"],"whenToPreferThis":"Choose this endpoint when you need a fast, pay-per-call computation of a Solidity function selector or event topic hash without setting up a local keccak256 library or Ethereum node. Ideal for AI agents building or verifying calldata on-the-fly, or for filtering EVM event logs by topic in automated workflows.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-17T12:41:00.216Z","isFirstParty":false,"canonicalSlug":"fastx402-solidity-selector-event-topic-calculator-84b478d7"}