klaviyo-webhooks

Klaviyo Webhooks

When to Use This Skill

• How do I receive Klaviyo webhooks?
• How do I verify Klaviyo webhook signatures (the Klaviyo-Signature header)?
• How do I handle Klaviyo system webhook events like event:klaviyo.opened_email?
• Why is my Klaviyo webhook signature verification failing?
• How do I secure a Klaviyo flow "Webhook" action that isn't signed?

Verification (core)

Klaviyo signs each system webhook with an HMAC-SHA256 over the raw request body concatenated with the Klaviyo-Timestamp header value, hex-encoded, using your endpoint secret (min 16 chars). The signature arrives in the Klaviyo-Signature header. Compute the same HMAC and compare timing-safe. There is no official SDK verification helper, so verify manually. Pass the raw body — don't JSON.parse first.

Node:

const crypto = require('crypto');

function verifyKlaviyoWebhook(rawBody, timestamp, signature, secret) {
  const computed = crypto
    .createHmac('sha256', secret)
    .update(rawBody)        // Buffer/string of the raw HTTP body
    .update(timestamp)      // Klaviyo-Timestamp header value, appended
    .digest('hex');
  try {
    return crypto.timingSafeEqual(Buffer.from(computed), Buffer.from(signature));
  } catch {
    return false;           // length mismatch = invalid
  }
}

Python:

import hmac, hashlib

def verify_klaviyo_webhook(raw_body: bytes, timestamp: str, signature: str, secret: str) -> bool:
    mac = hmac.new(secret.encode(), raw_body, hashlib.sha256)
    mac.update(timestamp.encode())          # append Klaviyo-Timestamp
    return hmac.compare_digest(mac.hexdigest(), signature)

For complete handlers with route wiring, event dispatch, and tests, see:

• examples/express/
• examples/nextjs/
• examples/fastapi/

Unsigned flow "Webhook" action

Signature verification above applies to system webhooks (created via the Webhooks API). Klaviyo's older flow "Webhook" action sends a custom JSON payload you define and is not signed. If signing is unavailable on your account, put a hard-to-guess secret token in the endpoint URL (e.g. /webhooks/klaviyo?token=…) and reject requests that don't match. See references/verification.md.