{"uid":"cap_Wo3jMgoe3MRAv9LaynJks","slug":"hmac-sha3-256-base64url-signing-service-10013e3b","name":"HMAC-SHA3-256 Base64url Signing Service","description":"Call when an agent needs an HMAC-sha3-256 of text with a caller-supplied key, encoded as base64url. Exact $0.006 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha3-256-base64url first.","url":"https://agentshelf.syntexa.ch/v1/hmac-sha3-256-base64url?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"key":{"type":"string","examples":["secret"],"maxLength":512,"minLength":1,"description":"HMAC secret. Required on HMAC SKUs. Omit it for plain digests and checksums. The key is not stored."},"text":{"type":"string","examples":["hello"],"maxLength":100000,"minLength":1,"description":"Message to digest. For raw-hex SKUs this is hex bytes; for utf16 or latin1 SKUs it is decoded with that encoding. Otherwise it is UTF-8 text."}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.006","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":"$0.006/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.006","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.006","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_QAltesAmd--0Dmhq2VCtK","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.006","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Computes an HMAC-SHA3-256 message authentication code for a given text using a caller-supplied key, returning the result encoded as base64url.","exampleAgentPrompt":"Compute the HMAC-SHA3-256 of the text 'Hello, World!' using the secret key 'mysecretkey123' and give me the result as a base64url string.","exampleUseCases":[{"title":"Webhook signature verification","prompt":"I need to sign this webhook payload 'user_id=42&event=purchase' with the key 'wh_secret_abc' using HMAC-SHA3-256 and get a base64url signature I can attach to the request header."},{"title":"API request authentication token","prompt":"Generate an HMAC-SHA3-256 base64url token for the string 'GET /api/orders/timestamp=1720000000' using the secret key 'api_secret_xyz' so I can authenticate my API call."},{"title":"Data integrity MAC for stored record","prompt":"I want to compute a message authentication code for the JSON string '{\"user\":\"alice\",\"role\":\"admin\"}' using HMAC-SHA3-256 with key 'integrity_key_99' encoded as base64url, so I can store it alongside the record to detect tampering."}],"resultDescription":"Returns a base64url-encoded HMAC-SHA3-256 digest of the provided text, computed using the caller-supplied key. The output is a compact, URL-safe string suitable for embedding in headers, query parameters, or tokens.","failureModes":["Empty or missing key field returns a validation error","Empty or missing text field returns a validation error","Text exceeding 100,000 characters is rejected","Key exceeding 512 characters is rejected","Payment failure or insufficient USDC balance returns a 402 error","Malformed request body returns a 400 error"],"whenToPreferThis":"Choose this endpoint when you specifically need HMAC-SHA3-256 (not HMAC-SHA256 or HMAC-SHA1) with base64url output encoding, for use cases like URL-safe tokens, webhook signing with modern hash functions, or when a downstream system explicitly requires SHA3-256. Use the free sandbox endpoint POST /v1/sandbox/hmac-sha3-256-base64url for testing before paying $0.006 USDC per call. Prefer this over SHA2-based HMAC endpoints when SHA3 is mandated by your security policy or API contract.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-02T06:50:20.465Z","isFirstParty":false,"canonicalSlug":"hmac-sha3-256-base64url-signing-service-10013e3b"}