# HMAC-SHA3-384 Base64URL Signer

> HMAC-SHA3-384 Base64URL Signer is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).

Computes an HMAC-SHA3-384 message authentication code of input text using a caller-supplied key, returning the result encoded as base64url.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha3-384-base64url?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-sha3-384-base64url-signer-d9823064
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_EdOPVKB80lr8VQRGAGzs1

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability hmac-sha3-384-base64url-signer-d9823064 -d '<json body>'
```

Example prompt: Compute the HMAC-SHA3-384 of the text 'Hello, world!' using the key 'my-secret-key-abc123' and give me the result as base64url.

## When to prefer this

Choose this endpoint when you specifically need HMAC-SHA3-384 (not SHA-256 or SHA-512) with base64url output encoding — for example, when interoperating with a system that requires SHA3-family MACs or URL-safe base64 encoding. Prefer the free sandbox variant (/v1/sandbox/hmac-sha3-384-base64url) for testing; use this paid endpoint in production or when the sandbox is unavailable.

## Known failure modes

- Missing or empty 'key' field returns a validation error
- Missing or empty 'text' field returns a validation error
- Key or text exceeding maximum length (512 and 100000 chars respectively) returns a 400 error
- Payment failure or insufficient USDC balance prevents the call from completing
- Malformed JSON request body results in a parse error

## How this service works

Call when an agent needs an HMAC-sha3-384 of text with a caller-supplied key, encoded as base64url. Exact $0.005 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha3-384-base64url first.

## Output

Returns a base64url-encoded HMAC-SHA3-384 digest computed over the provided text using the supplied key. The output is a compact, URL-safe string suitable for use as a signature or MAC in headers, query parameters, or storage.

## Request schema (JSON Schema)

```json
{
 "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."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hmac-sha3-384-base64url-signer-d9823064/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)