{"uid":"cap_BuMPHvvglfyb2Dge3LDM0","slug":"hmac-sha256-base64url-signer-52bf9c6d","name":"HMAC-SHA256 Base64URL Signer","description":"Call when an agent needs an HMAC-sha256 of text with a caller-supplied key, encoded as base64url. Exact $0.007 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha256-base64url first.","url":"https://agentshelf.syntexa.ch/v1/hmac-sha256-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":"0.007","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":"$0.007/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.007","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.007","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_FaNMTJSFp69yyypXxh6QC","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.007","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Computes an HMAC-SHA256 message authentication code of input text using a caller-supplied key, returning the result encoded as base64url.","exampleAgentPrompt":"Compute an HMAC-SHA256 signature of the text 'order_id=42&amount=99.99' using the secret key 'mysecretkey123' and give me the result as a base64url string.","exampleUseCases":[{"title":"Webhook payload signing","prompt":"Sign this webhook payload 'user_id=88&event=purchase&ts=1720000000' with the shared secret 'wh_secret_abc' using HMAC-SHA256 and return it as base64url so I can attach it to the X-Signature header."},{"title":"API request authentication","prompt":"I need to authenticate my API request — compute an HMAC-SHA256 over the string 'GET /orders/2024-07-01' using key 'api_key_xyz' and give me the base64url digest."},{"title":"Data integrity verification token","prompt":"Generate an HMAC-SHA256 base64url tag for the message 'invoice:INV-2024-001:total:500' with secret 'inv_signing_key' so I can store it alongside the record and verify it hasn't been tampered with later."}],"resultDescription":"Returns a base64url-encoded HMAC-SHA256 digest string computed over the input text using the provided key. No network calls or LLM are involved — the result is deterministic and repeatable for the same key and text.","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 (insufficient USDC balance) blocks the call; try the free sandbox endpoint /v1/sandbox/hmac-sha256-base64url first"],"whenToPreferThis":"Choose this endpoint when you need a standards-compliant HMAC-SHA256 digest encoded specifically as base64url (URL-safe, no padding issues) rather than hex or standard base64. Prefer it over the sibling HMAC-SHA384/SHA512 variants when SHA-256 compatibility is required (e.g. AWS Signature V4, JWT HS256, GitHub webhooks). Use the free sandbox variant first to validate your key/text inputs before paying.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-02T06:50:15.569Z","isFirstParty":false,"canonicalSlug":"hmac-sha256-base64url-signer-52bf9c6d"}