# HMAC-SHA256 Message Authentication

> HMAC-SHA256 Message Authentication is a paid API for AI agents from x402render-u5vwpxpyua-uc.a.run.app, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Computes an HMAC-SHA256 digest of a given text string using a provided secret key

## Facts

- Endpoint: POST https://x402render-u5vwpxpyua-uc.a.run.app/hmac-sha256
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-sha256-message-authentication-462d62eb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_yY_aOWUQkTXZkAA96oRl_

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-sha256-message-authentication-462d62eb -d '<json body>'
```

Example prompt: Compute an HMAC-SHA256 signature for the message 'order_id=12345&amount=99.99' using my secret key 'mySuperSecretKey2024'.

## When to prefer this

Choose this endpoint when you need a simple, stateless HMAC-SHA256 computation as a service without setting up local crypto libraries — especially useful in low-code or agent workflows where running native crypto code is inconvenient. Prefer it over generic hashing endpoints (MD5, SHA-512 siblings) when you need keyed authentication rather than a plain hash, and when the $0.01 per-call cost is acceptable for on-demand signing.

## Known failure modes

- Missing 'key' or 'text' field in request body returns a 400 error
- Empty string key or text may produce a valid but trivially weak HMAC
- Payment not attached or insufficient USDC balance results in 402 Payment Required
- Server error on the cloud run instance returns 500 with no digest

## How this service works

HMAC-SHA256 of a string with a secret key

## Output

Returns the HMAC-SHA256 hexadecimal digest (message authentication code) computed from the input text using the provided secret key, allowing the caller to authenticate or verify the integrity of the original message.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "key": {
   "type": "string",
   "description": "string"
  },
  "text": {
   "type": "string",
   "description": "string"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hmac-sha256-message-authentication-462d62eb/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402render-u5vwpxpyua-uc.a.run.app](https://www.zero.xyz/host/x402render-u5vwpxpyua-uc.a.run.app/llms.txt)