# HMAC-SHA3-256 Hex Digest

> HMAC-SHA3-256 Hex Digest is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-29).

Computes an HMAC-SHA3-256 message authentication code for a given text and key, returning the result as a lowercase hex string.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-sha3-256-hex?utm_source=zero.xyz
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-sha3-256-hex-digest-c90201a9
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_wY-Jxcp4YbHJCXGZjtqEK

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-sha3-256-hex-digest-c90201a9 -d '<json body>'
```

Example prompt: Compute the HMAC-SHA3-256 of the text 'Hello, world!' using the secret key 'mysecretkey' and give me the result as a hex string.

## When to prefer this

Choose this endpoint when you specifically need HMAC-SHA3-256 (not HMAC-SHA256 or other variants) with hex-encoded output and have a caller-supplied secret key. Prefer the free sandbox endpoint POST /v1/sandbox/hmac-sha3-256-hex for testing before spending $0.004 USDC per call on this paid version. Use this over generic hashing endpoints when a keyed MAC (not a plain digest) is required for authentication or integrity verification.

## Known failure modes

- Key or text is empty or exceeds length limits (400 Bad Request)
- Text exceeds 100,000 character limit
- Key exceeds 512 character limit
- Insufficient USDC balance for $0.004 payment (402 Payment Required)
- Network timeout or server unavailability (503)

## How this service works

Call when an agent needs an HMAC-sha3-256 of text with a caller-supplied key, encoded as hex. Exact $0.004 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha3-256-hex first.

## Output

A hex-encoded HMAC-SHA3-256 string (64 lowercase hex characters) computed from the provided text and key, confirming message authenticity and integrity.

## 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-sha3-256-hex-digest-c90201a9/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)