# HMAC-SHA224 Base64URL Signer

> HMAC-SHA224 Base64URL Signer is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-29).

Computes an HMAC-SHA224 digest of input text using a caller-supplied key and returns it encoded as base64url.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha224-base64url?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-sha224-base64url-signer-58433c72
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_qBkNymeTddxF1elj__91R

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-base64url-signer-58433c72 -d '<json body>'
```

Example prompt: Can you compute the HMAC-SHA224 of the text 'hello world' using the key 'mysecretkey' and give me the result as a base64url string?

## When to prefer this

Choose this endpoint when you specifically need HMAC-SHA224 (not SHA256 or SHA512) output encoded as base64url rather than hex. It is ideal for agents that need a simple, stateless, paid cryptographic signing primitive without managing local crypto libraries. Use the free sandbox endpoint (/v1/sandbox/hmac-sha224-base64url) for testing before incurring the $0.002 USDC per-call charge.

## Known failure modes

- Empty or missing key returns validation error
- Text exceeding 100,000 characters is rejected
- Empty text returns validation error
- Key exceeding 512 characters is rejected
- Malformed request body returns 400 error
- Payment failure or insufficient USDC balance blocks the call

## How this service works

Call when an agent needs an HMAC-sha224 of text with a caller-supplied key, encoded as base64url. Exact $0.002 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha224-base64url first.

## Output

Returns a base64url-encoded HMAC-SHA224 digest string computed from the provided text and key. The digest is a fixed-length cryptographic authentication code that can be used for integrity verification or message 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-sha224-base64url-signer-58433c72/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)