# HMAC-SHA384 Base64 Signer

> HMAC-SHA384 Base64 Signer is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.009/call, status unknown (last checked 2026-09-29).

Computes an HMAC-SHA384 signature of input text using a caller-supplied key and returns it encoded as Base64.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha384-base64?utm_source=zero.xyz
- Price: $0.009/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-sha384-base64-signer-73d08234
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_DH7h4DKH_y7-zYtcJcx_7

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-sha384-base64-signer-73d08234 -d '<json body>'
```

Example prompt: Can you compute the HMAC-SHA384 of the text 'invoice:12345:amount:99.00' using the secret key 'my-super-secret-key-42' and give me the result as Base64?

## When to prefer this

Choose this endpoint when you need HMAC-SHA384 specifically (stronger than SHA256) and want the output as Base64. If cost is a concern, try the free sandbox endpoint at /v1/sandbox/hmac-sha384-base64 first. Prefer this paid endpoint for production use or when the sandbox is unavailable.

## Known failure modes

- Empty or missing key (minLength:1 violated) returns validation error
- Text exceeds 100,000 character limit returns 413 or validation error
- Missing required fields returns 400 bad request
- Payment of $0.009 USDC not provided or declined returns 402 Payment Required
- Malformed JSON body returns 400

## How this service works

Call when an agent needs an HMAC-sha384 of text with a caller-supplied key, encoded as base64. Exact $0.009 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha384-base64 first.

## Output

Returns a Base64-encoded string containing the HMAC-SHA384 digest of the input text computed with the provided secret key. This is a fixed-length, deterministic authentication code that can be used for message integrity verification or authentication.

## 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-sha384-base64-signer-73d08234/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)