# HMAC-SHA224 Hex Digest API

> HMAC-SHA224 Hex Digest API is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-02).

Computes an HMAC-SHA224 message authentication code for a given text using a caller-supplied key, returning the result as a lowercase hex string.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha224-hex?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-sha224-hex-digest-api-b461e5bb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_MK4sKIXuwqnbgSWFEdN-z

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-sha224-hex-digest-api-b461e5bb -d '<json body>'
```

Example prompt: Compute the HMAC-SHA224 hex digest of the text 'Hello, World!' using the secret key 'mysecretkey123'.

## When to prefer this

Choose this endpoint when you specifically need HMAC-SHA224 (not SHA-256 or SHA-512) as a keyed hash for message authentication or integrity verification, and when a hex-encoded output is required. Prefer the free sandbox endpoint POST /v1/sandbox/hmac-sha224-hex during development or testing to avoid the $0.01 USDC charge. Use this paid endpoint for production workloads where reliable uptime and SLA matter.

## Known failure modes

- Missing or empty key parameter returns a validation error
- Missing or empty text parameter returns a validation error
- Text exceeding 100,000 characters is rejected
- Key exceeding 512 characters is rejected
- Payment failure or insufficient USDC balance prevents the call from completing
- Network timeout may occur under load

## How this service works

Call when an agent needs an HMAC-sha224 of text with a caller-supplied key, encoded as hex. Exact $0.01 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha224-hex first.

## Output

Returns a hex-encoded HMAC-SHA224 digest string (56 hex characters) computed over the provided text using the supplied key. The response is a deterministic, fixed-length authentication code that can be used for message integrity verification or API request signing.

## 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-sha224-hex-digest-api-b461e5bb/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)