HMAC

HMAC signature of a message with a shared key. Algorithms: sha256 (default), sha512, sha1. Returns hex and base64.

Input

Field	Type	Description
text *	string	Message to sign (max 100KB)
key *	string	Shared secret key
algo	string	sha256 | sha512 | sha1

Example output

{
  "algo": "sha256",
  "hex": "f7bc…",
  "base64": "97w…"
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/hmac \
  -H "Content-Type: application/json" \
  -d '{"text":"payload","key":"secret","algo":"sha256"}'

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/hmac", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "text": "payload",
    "key": "secret",
    "algo": "sha256"
  }),
});

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