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HMAC-SHA3-256 Base64url Signing Service
x402
HMAC-SHA3-256 Base64url Signing Service is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.006/call, status unknown (last checked 2026-09-29).
Computes an HMAC-SHA3-256 message authentication code for a given text using a caller-supplied key, returning the result encoded as base64url.
Price / call$0.006
Success—
StatusUnknown
How this service works
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.
Output
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.
Example use cases
Webhook signature verification
“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.”
API request authentication token
“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.”
Data integrity MAC for stored record
“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.”
Technical details
Endpoint
POSThttps://agentshelf.syntexa.ch/v1/hmac-sha3-256-base64url?utm_source=zero.xyzWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| key | string | HMAC secret. Required on HMAC SKUs. Omit it for plain digests and checksums. The key is not stored. |
| text | string | 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. |
Tags
x402
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