# agentshelf.syntexa.ch HMAC-BLAKE2s256 Hex

> agentshelf.syntexa.ch HMAC-BLAKE2s256 Hex is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.007/call, status unknown (last checked 2026-10-02).

Computes an HMAC using the BLAKE2s-256 hash function with a caller-supplied key over input text, returning the result as a lowercase hex string.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-blake2s256-hex?utm_source=zero.xyz
- Price: $0.007/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agentshelf-syntexa-ch-hmac-blake2s256-hex-f14c45ca
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_nWW_tEUnqQc4Mok3XZ2fR

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-blake2s256-hex-f14c45ca -d '<json body>'
```

Example prompt: Can you compute the HMAC-BLAKE2s256 hex digest of the text 'hello world' using the secret key 'mysecretkey123'?

## When to prefer this

Choose this endpoint when you need a BLAKE2s-256 based HMAC specifically — as opposed to SHA-256 or SHA-512 HMAC — because BLAKE2s is faster on constrained hardware and provides comparable security. Use it when your protocol or counterparty requires BLAKE2s keyed authentication. If cost is a concern, try the free sandbox endpoint POST /v1/sandbox/hmac-blake2s256-hex first.

## Known failure modes

- Missing or empty 'key' field returns a validation error
- Missing or empty 'text' field returns a validation error
- Text exceeding 100,000 characters returns a length error
- Key exceeding 512 characters returns a validation error
- Payment of $0.007 USDC not provided or rejected triggers HTTP 402
- Network timeout if the service is temporarily unavailable

## How this service works

Call when an agent needs an HMAC-blake2s256 of text with a caller-supplied key, encoded as hex. Exact $0.007 USDC. Prefer unpaid POST /v1/sandbox/hmac-blake2s256-hex first.

## Output

Returns a hex-encoded HMAC-BLAKE2s256 digest string computed over the provided text using the supplied key. The output is a fixed-length lowercase hexadecimal string representing the 256-bit MAC.

## 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-blake2s256-hex-f14c45ca/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)