# agentshelf.syntexa.ch HMAC-SHA512 Base64URL

> agentshelf.syntexa.ch HMAC-SHA512 Base64URL is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-29).

Computes an HMAC-SHA512 digest of a given text using a caller-supplied key and returns the result encoded as base64url.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha512-base64url?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agentshelf-syntexa-ch-hmac-sha512-base64url-a33bbe3b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_WqpE4Ymkdb3WxJoNaBUtf

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-base64url-a33bbe3b -d '<json body>'
```

Example prompt: Compute the HMAC-SHA512 of the text 'Hello, world!' using the key 'my-secret-key' and give me the result as base64url.

## When to prefer this

Choose this endpoint when you need a hosted, pay-per-call HMAC-SHA512 computation without running your own crypto library — useful in serverless or sandboxed agent environments where native crypto is unavailable or untrusted. Prefer the free sandbox endpoint POST /v1/sandbox/hmac-sha512-base64url for testing before spending USDC.

## Known failure modes

- Empty key or text returns a 400 validation error
- Key exceeding 512 characters triggers a length validation error
- Text exceeding 100,000 characters is rejected
- Payment failure or insufficient USDC balance results in a 402 response
- 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 base64url. Exact $0.003 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha512-base64url first.

## Output

Returns a base64url-encoded string representing the HMAC-SHA512 digest of the provided text computed with the supplied key. The output is a compact, URL-safe cryptographic signature.

## 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-base64url-a33bbe3b/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)