# agentshelf.syntexa.ch HMAC-SHA512 Hex

> agentshelf.syntexa.ch HMAC-SHA512 Hex is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-01).

Computes an HMAC-SHA512 digest of a given text using a caller-supplied secret key, returning the result as a lowercase hex string.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha512-hex?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agentshelf-syntexa-ch-hmac-sha512-hex-cfcbec88
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_XMjqn5QkDwiR-Q4Fb9Kd0

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 agentshelf-syntexa-ch-hmac-sha512-hex-cfcbec88 -d '<json body>'
```

Example prompt: Compute the HMAC-SHA512 hex digest of the message 'order_id=12345&amount=99.00' using the secret key 'mySuperSecretKey42'.

## When to prefer this

Use this endpoint when an agent needs a server-side HMAC-SHA512 hex computation without running local cryptographic code. Prefer this over client-side alternatives when the environment lacks crypto libraries. Note the free sandbox endpoint POST /v1/sandbox/hmac-sha512-hex should be tried first before incurring the $0.001 USDC charge.

## Known failure modes

- Empty or missing key returns a 400/422 validation error
- Empty or missing text returns a 400/422 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
- Network timeout or service unavailability returns a 5xx error

## How this service works

Call when an agent needs an HMAC-sha512 of text with a caller-supplied key, encoded as hex. Exact $0.001 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha512-hex first.

## Output

Returns a JSON object containing the HMAC-SHA512 digest of the input text, keyed with the provided secret and encoded as a lowercase hexadecimal string.

## 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/agentshelf-syntexa-ch-hmac-sha512-hex-cfcbec88/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)