ETH transfer notifications, delivered as webhooks

POST /webhooks/chainhook HTTP/1.1
Host: api.example.com
Content-Type: application/json
User-Agent: chainhook/1.x
X-Webhook-Id: 01a0fbfd-4fe4-7a3c-8f21-6b9d0e4c7a15
X-Webhook-Signature: 7a12d02673420517279805cf8188a1a62c6f69706161ba5cf0a8ec91ea66b8e3

{
  "id": "01a0fbfd-4fe4-7a3c-8f21-6b9d0e4c7a15",
  "event": "transfer.detected",
  "created_at": "2026-10-02T09:41:17Z",
  "webhook_id": "01a0fbf2-fadc-7c3e-9b1a-4d6f2e8a5c71",
  "data": {
    "network": "ethereum",
    "direction": "in",
    "type": "native",
    "transaction_hash": "0xb8b13bbf4e3cadb956fa055924afe17ef79ebd6a7733e06b1336ca04dfcb1d1b",
    "transfer_index": 0,
    "block_number": 26239160,
    "block_hash": "0x76baf9e38816fa75a1f64ff4c19c2a6272a9624bb8d0aa2c7ce5ba6a248077da",
    "block_timestamp": "2026-10-02T09:41:05Z",
    "confirmations": 12,
    "from": "0x865658a2269a5c9333110fd34ea6e143631feffd",
    "to": "0x2cd4fa2207e4483ecef691fda178f1b6401a8055",
    "currency": "ETH",
    "amount": "0.25",
    "amount_raw": "250000000000000000",
    "decimals": 18,
    "contract_address": null
  }
}

import crypto from 'node:crypto';
import express from 'express';

const app = express();

app.post(
  '/webhooks/chainhook',
  express.raw({ type: 'application/json' }),
  (req, res) => {
    const signature = req.get('X-Webhook-Signature') ?? '';
    const expected = crypto
      .createHmac('sha256', process.env.CHAINHOOK_SIGNING_SECRET)
      .update(req.body)
      .digest('hex');

    const valid =
      signature.length === expected.length &&
      crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));

    if (!valid) {
      return res.sendStatus(401);
    }

    const event = JSON.parse(req.body);
    // Skip event.id if you've already processed it.

    res.sendStatus(200);
  },
);