Sendgrid Webhooks

SendGrid Webhooks

When to Use This Skill

• Setting up SendGrid webhook handlers for email delivery tracking
• Debugging ECDSA signature verification failures
• Processing email events (bounce, delivered, open, click, spam report)
• Implementing email engagement analytics

Essential Code

Signature Verification (Manual)

SendGrid uses ECDSA (Elliptic Curve Digital Signature Algorithm) with public key verification.

// Node.js manual verification
const crypto = require('crypto');

function verifySignature(publicKey, payload, signature, timestamp) {
  // Decode the base64 signature
  const decodedSignature = Buffer.from(signature, 'base64');

  // Create the signed content
  const signedContent = timestamp + payload;

  // Create verifier
  const verifier = crypto.createVerify('sha256');
  verifier.update(signedContent);

  // Add PEM headers if not present
  let pemKey = publicKey;
  if (!pemKey.includes('BEGIN PUBLIC KEY')) {
    pemKey = `-----BEGIN PUBLIC KEY-----\n${publicKey}\n-----END PUBLIC KEY-----`;
  }

  // Verify the signature
  return verifier.verify(pemKey, decodedSignature);
}

// Express middleware
app.post('/webhooks/sendgrid', express.raw({ type: 'application/json' }), (req, res) => {
  const signature = req.get('X-Twilio-Email-Event-Webhook-Signature');
  const timestamp = req.get('X-Twilio-Email-Event-Webhook-Timestamp');

  if (!signature || !timestamp) {
    return res.status(400).send('Missing signature headers');
  }

  const publicKey = process.env.SENDGRID_WEBHOOK_VERIFICATION_KEY;
  const payload = req.body.toString();

  if (!verifySignature(publicKey, payload, signature, timestamp)) {
    return res.status(400).send('Invalid signature');
  }

  // Process events
  const events = JSON.parse(payload);
  console.log(`Received ${events.length} events`);

  res.sendStatus(200);
});

Using SendGrid SDK

const { EventWebhook } = require('@sendgrid/eventwebhook');

const verifyWebhook = new EventWebhook();
const publicKey = process.env.SENDGRID_WEBHOOK_VERIFICATION_KEY;

app.post('/webhooks/sendgrid', express.raw({ type: 'application/json' }), (req, res) => {
  const signature = req.get('X-Twilio-Email-Event-Webhook-Signature');
  const timestamp = req.get('X-Twilio-Email-Event-Webhook-Timestamp');

  const isValid = verifyWebhook.verifySignature(
    publicKey,
    req.body,
    signature,
    timestamp
  );

  if (!isValid) {
    return res.status(400).send('Invalid signature');
  }

  // Process webhook
  res.sendStatus(200);
});

Common Event Types

Environment Variables

# Your SendGrid webhook verification key (public key)
SENDGRID_WEBHOOK_VERIFICATION_KEY="MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE..."

Local Development

For local webhook testing, use Hookdeck CLI:

brew install hookdeck/hookdeck/hookdeck
hookdeck listen 3000 --path /webhooks/sendgrid

No account required. Provides local tunnel + web UI for inspecting requests.

Resources

• overview.md - What SendGrid webhooks are, common event types
• setup.md - Configure webhooks in SendGrid dashboard, get verification key
• verification.md - ECDSA signature verification details and gotchas
• examples/ - Complete implementations for Express, Next.js, and FastAPI

Related Skills

• webhook-handler-patterns - Cross-cutting patterns (idempotency, retries, framework guides)
• hookdeck-event-gateway - Production infrastructure (routing, replay, monitoring)