Agent skill

Adyen Webhooks Skill

Receive and verify Adyen webhooks (standard notifications). Use when setting up Adyen webhook handlers, debugging HMAC signature verification, or handling payment events like AUTHORISATION, CAPTURE, REFUND, CANCELLATION, and CHARGEBACK.

Install this skill

npx skills add hookdeck/webhook-skills --skill adyen-webhooks

When to Use This Skill

How do I receive Adyen webhooks (standard notifications)?
How do I verify Adyen webhook HMAC signatures?
How do I handle AUTHORISATION, CAPTURE, REFUND, or CHARGEBACK events?
Why is my Adyen HMAC signature verification failing?
What response body does Adyen expect from my webhook endpoint?

How Adyen Webhooks Work

Adyen sends standard notifications as an HTTP POST with a JSON body containing a batch of notificationItems. Each item wraps a NotificationRequestItem:

{
  "live": "false",
  "notificationItems": [
    {
      "NotificationRequestItem": {
        "eventCode": "AUTHORISATION",
        "success": "true",
        "pspReference": "7914073381342284",
        "merchantAccountCode": "TestMerchant",
        "merchantReference": "TestPayment-1407325143704",
        "amount": { "value": 1130, "currency": "EUR" },
        "additionalData": { "hmacSignature": "coqCmt/IZ4E3CzPvMY8zTjQVL5hYJUiBRg8UU+iCWo0=" }
      }
    }
  ]
}

Your endpoint must:

Verify the HMAC signature on each item (additionalData.hmacSignature).
Acknowledge with the literal body [accepted] and HTTP 200 — otherwise Adyen retries.

Verification (core)

Adyen's HMAC is not computed over the raw request body. It is computed over a :-delimited string of specific fields, in this exact order:

pspReference : originalReference : merchantAccountCode : merchantReference : amount.value : amount.currency : eventCode : success

Each field value is escaped (\ → \\, : → \:), empty fields become empty strings, and the HMAC key from the Customer Area is a hex string that must be hex-decoded before use. The result is HMAC-SHA256, base64-encoded, and compared against additionalData.hmacSignature. Because the signature covers parsed fields, you parse the JSON first, then verify each item.

The official @adyen/api-library SDK does all of this for you:

const { hmacValidator } = require('@adyen/api-library');

const validator = new hmacValidator();

// item = notificationItems[i].NotificationRequestItem (plain parsed object)
// ADYEN_HMAC_KEY = hex string from the Customer Area
const valid = validator.validateHMAC(item, process.env.ADYEN_HMAC_KEY);
// reads item.additionalData.hmacSignature and compares (timing-safe) internally

No Node SDK (e.g. Python/FastAPI)? Reproduce the algorithm manually:

import hmac, hashlib, base64, binascii

def calculate_hmac(item, hex_key):
    a = item.get("amount") or {}
    fields = [item.get("pspReference", ""), item.get("originalReference", ""),
              item.get("merchantAccountCode", ""), item.get("merchantReference", ""),
              a.get("value", ""), a.get("currency", ""),
              item.get("eventCode", ""), item.get("success", "")]
    data = ":".join(str(f).replace("\\", "\\\\").replace(":", "\\:") for f in fields)
    key = binascii.unhexlify(hex_key)  # hex → bytes
    return base64.b64encode(hmac.new(key, data.encode("utf-8"), hashlib.sha256).digest()).decode()

# hmac.compare_digest(calculate_hmac(item, key), item["additionalData"]["hmacSignature"])

For complete handlers with route wiring, event dispatch, Basic Auth, and tests, see:
examples/express/
examples/nextjs/
examples/fastapi/

Common Event Types

`eventCode`	Triggered When
`AUTHORISATION`	A payment was authorised (check `success` for the outcome)
`CAPTURE`	Authorised funds were captured
`CAPTURE_FAILED`	A capture attempt failed
`REFUND`	A refund was processed
`REFUND_FAILED`	A refund attempt failed
`CANCELLATION`	An authorisation was cancelled
`CANCEL_OR_REFUND`	A payment was cancelled or refunded
`CHARGEBACK`	Funds were reversed by the shopper's bank
`NOTIFICATION_OF_CHARGEBACK`	A chargeback dispute was opened
`REPORT_AVAILABLE`	A generated report is ready to download

Important: Always check the success field — an AUTHORISATION with success: "false" means the payment was refused, not approved.

For the full event reference, see Adyen webhook types.

Environment Variables

ADYEN_HMAC_KEY=YOUR_HEX_HMAC_KEY        # Hex string generated in the Customer Area
# Optional Basic Auth (recommended) — configured alongside the webhook in the Customer Area
ADYEN_WEBHOOK_USERNAME=your_username
ADYEN_WEBHOOK_PASSWORD=your_password

Local Development

# Start tunnel (no account needed)
npx hookdeck-cli listen 3000 adyen --path /webhooks/adyen

Reference Materials

references/overview.md - Adyen webhook concepts and event types
references/setup.md - Configure webhooks in the Customer Area, generate the HMAC key
references/verification.md - HMAC signature verification details and gotchas