Agent402 / tools / webhook-verify

Webhook signature verify

FREE with proof-of-work · or $0.001 in USDC · POST /api/webhook-verify

Verify a webhook's HMAC signature against the correct per-provider scheme: GitHub (X-Hub-Signature-256, sha256=hex), Stripe (Stripe-Signature t/v1 over "<t>.<body>" with replay tolerance), Shopify (X-Shopify-Hmac-Sha256, base64), Slack (X-Slack-Signature, v0:<ts>:<body> with replay tolerance). Constant-time comparison; the secret is never echoed. Pass the RAW request body string — signatures are over the raw bytes. Deterministic.

Input

Field	Type	Description
`provider` *	string	github \| stripe \| shopify \| slack
`payload` *	string	the RAW request body string, byte-for-byte as received (never a re-serialized object)
`secret` *	string	the provider signing secret (never echoed back)
`signature` *	string	the signature header value, with or without its scheme prefix (sha256= / v0= / t=...,v1=...)
`timestamp`	string	provider timestamp, required for stripe + slack (stripe may be parsed from a t= element in the signature)
`toleranceSeconds`	number	max timestamp age for stripe/slack replay protection (default 300; 0 skips the age check)

Example output

{
  "valid": true,
  "provider": "github",
  "scheme": "X-Hub-Signature-256: sha256=hex(HMAC-SHA256(secret, rawBody))",
  "reason": "signature matches the recomputed HMAC for this payload and secret"
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/webhook-verify \
  -H "Content-Type: application/json" \
  -d '{"provider":"github","payload":"{\"hello\":\"world\"}","secret":"it's a secret","signature":"sha256=8d4063f0a81aa1531d9891a028a68cf2bb537ecdf0e82557674d71e168d570f9"}'

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/webhook-verify", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "provider": "github",
    "payload": "{\"hello\":\"world\"}",
    "secret": "it's a secret",
    "signature": "sha256=8d4063f0a81aa1531d9891a028a68cf2bb537ecdf0e82557674d71e168d570f9"
  }),
});

No wallet? Pay with compute

This is a pure-CPU tool, so an agent without a wallet can pay with proof-of-work instead of USDC: fetch a challenge, solve the sha256 puzzle (16 leading zero bits — a fraction of a second of CPU, no money, no AI tokens), and resend with the X-Pow-Solution header.

import { createHash } from "node:crypto";
const lz = (b) => { let t = 0; for (const x of b) { if (!x) { t += 8; continue; } t += Math.clz32(x) - 24; break; } return t; };
const c = await (await fetch("https://agent402.tools/api/pow/challenge?slug=webhook-verify")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/webhook-verify", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"provider":"github","payload":"{\"hello\":\"world\"}","secret":"it's a secret","signature":"sha256=8d4063f0a81aa1531d9891a028a68cf2bb537ecdf0e82557674d71e168d570f9"}) });

Part of these workflows

This tool is one step in a curated multi-tool workflow — agents can fetch the whole sequence as an MCP prompt or call https://agent402.tools/api/skill-packs/{slug}/prompt.

Webhook secure intake — The production ingest path for every incoming webhook: verify the provider signature (GitHub / Stripe / Shopify / Slack, constant-time, replay-window enforced), schema-validate the now-trusted body against the provider envelope, fingerprint the raw bytes for redelivery dedup, normalize the event timestamp to UTC + epoch, and redact PII before anything hits a log. Five pure-CPU tools — the accept-or-reject gate, run on every event.

Webhook signature verify

Input

Example output

Try it — see the 402 challenge (free)

Paid call (JavaScript agent)

No wallet? Pay with compute

Part of these workflows

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